3 How do Food and Drugs Influence my Brain?
3 How do Food and Drugs Influence my Brain?
- Gary L. Wenk
The brain is the organ of your mind; therefore, food and drugs can have a profound influence on how you think, act, and feel. These effects can be profound, subtle, or barely noticeable. Why do some chemicals in your diet affect your brain and how you feel, while others do not? Many drugs or nutrients that potentially might influence brain function are never able to enter the brain because of the presence of a series of barriers; the most important of these is the blood–brain barrier.
This barrier allows the easy entry of drugs and nutrients that are lipid-soluble (i.e., fat-soluble) and restricts the entry of drugs and nutrients that are water-soluble. Extremely lipid-soluble drugs enter the brain rapidly; they also tend to exit rather rapidly, which reduces the duration of their action. Some familiar examples of lipid-soluble nutrients are the vitamins A, D, E, and K. Nicotine and caffeine are also quite lipid-soluble and enter the brain easily; if they did not, then it is highly unlikely that anyone would bother consuming them so often. Take a moment to appreciate how this fact has been an incredible boon to the evolutionary success of tobacco and coffee plants: their discovery by our species, coupled with the fortuitous nature of our brain chemistry, led to their widespread cultivation and protection as two of the most important plants on earth. Human behavior has impacted these plants as much as they have impacted human history; for example, the p. 42↵introduction of coffee and tea fueled the Enlightenment and the Industrial Revolution.
This chapter will discuss the foods and drugs that affect your brain and, thereby, your behavior. The distinction between what is considered a drug (i.e., something that your body wants or needs to function optimally) and food (i.e., something that your body wants or needs to function optimally) is becoming increasingly difficult to define. Indeed, the routine use of some substances, such as stimulants and depressants, is so universal that most of us do not even consider them to be drugs but, rather, actual food. Are coffee, tea, tobacco, alcohol, cocoa, or marijuana nutrients or drugs? For many people, the distinction has become rather meaningless because their body craves many of these substances at all times. Obviously, anything you take into your body should be considered a drug whether it is nutritious or not. For the remainder of this chapter, I will make no distinction between drugs and food: they are essentially just chemicals that have unique effects on the body.
The foods we eat and many of our most popular psychoactive drugs often come from plants. Many plants contain chemicals that are very similar to the chemicals in our brains. The similar nature of these chemicals underlies why the contents of our diets can influence brain function.
Why do plants affect the human brain?
Plants produce chemicals that are capable of affecting our brain because they share an evolutionary history with us on this planet. Even primitive one-celled organisms produce many of the same chemicals that are in your brain. Therefore, whether you choose to eat a bunch of broccoli or a large pile of amoeba, the chemicals they contain may alter how your neurons function and, therefore, how you feel or think.
The fact that you share an evolutionary history with insects and reptiles also underlies the ability of venoms to produce the p. 43↵unpleasant affects you feel if you are stung by a bee or bitten by a snake. The bugs add serotonin to their venom in order to increase blood flow to the site of the bite or sting, thus increasing the chances that you will absorb most of the venom. Our shared history with plants and animals here on earth leads to some interesting predictions. For example, consider the following science fiction scenario: A spaceman is walking on an earth-like planet and is suddenly bitten by an unfriendly and grizzly looking creature. The spaceman can see that he is injured and that a liquid substance was injected under his skin by the beast. Does he die? No, he does not die, because his species and that of the creature on this foreign planet do not share an evolutionary past or a common ancestor. Their independent evolutionary paths make it highly improbable that they use similar neurotransmitter molecules within their respective brains and bodies.
Back on earth, people in ancient cultures were certainly very aware of the unique properties of certain plants and of the consequences of consuming them; indeed, they often sought them out as remedies for a variety of physical illnesses. This ancient use of plant extracts as medicines was also likely the beginning of a long series of reforms in our concept of how the brain functions and what its role is as the organ of the mind. For example, the realization that it might be possible to treat mental illness in the same way that one treats physical illness—that is, by using drugs or diet—was slow to gain general approval in part because of the wide-ranging, and for some still quite frightening, implications about what this meant regarding the nature of the human mind. Our grandchildren will likely have a whole host of highly modified chemicals added to their diets strategically designed to enhance a broad range of mental functions. In fact, we already do have a vast pharmacopeia, legal and otherwise, that can affect the brain, and no end of debate about its value and effectiveness.
Three basic principles apply to any substance you ingest that might affect your brain. First, these substances should not be p. 44↵viewed as being either “good” or “bad.” Drugs and nutrients in your diet are simply chemicals—no more, no less. They initiate actions within your brain that you either desire or would like to avoid. Second, everything you consume likely has multiple effects. Because your brain and body are so complex and because the chemicals you ingest are free to act in many different areas of your brain and body at the same time, they will often have many different effects—both direct and indirect—on your brain function and behavior. Third, the effect of a drug or nutrient on your brain always depends on the amount consumed. Varying the dose of any particular chemical changes the magnitude and the character of its effects. This principle is called the “dose–response effect”; that is, in general, greater doses lead to greater effects on your brain. Sometimes, however, greater doses produce completely opposite effects from those of lower doses. For example, aspirin reduces body temperature when taken at normal therapeutic doses but increases body temperature when taken at high doses.
How do we become addicted to specific foods and drugs?
Sometimes the effects of certain chemicals are present in the brain for so long that the brain slowly adjusts to their presence. Over time, the brain acts as though the drug or nutrient has become a necessary component of normal brain function. You experience your brain’s adjustment to the eventual absence of this substance as craving. Consider, for example, the very powerful drug, sugar. Your brain needs sugar (usually in the form of glucose) to function normally. The many billions of neurons in your brain require a constant supply of glucose to maintain their ability to produce energy and communicate with other neurons. The brain consumes the equivalent of about 12 donuts worth of glucose every day. Neurons can tolerate a deprivation of glucose for only a few minutes before they begin to die. Therefore, as blood levels of sugar decrease with the passage of time since your last meal, you begin to p. 45↵experience a craving for food, preferably something sweet. The presence of sugar in your brain is considered normal, and its absence leads to the feeling of craving and the initiation of hunting or foraging behaviors, such as seeking out a vending machine for a chocolate bar. If you wish to experience the truly overwhelming and powerful nature of drug craving, just stop eating for a full day.
Now you can easily recognize a parallel with the experience of a heroin addict. Within a few hours you will not be able to think of anything but food (heroin), you will do anything, sell anything, or steal from anyone to get food (heroin); as time passes, nothing is more important to you than the next meal (shot of heroin). The brain behaves as though it cannot tell the difference between a food and a drug; they are both just chemicals. The constant consumption of caffeine, nicotine, or almost any chemical can produce similar types of compensatory changes within your brain and lead to craving when they are absent from the brain. This response is exactly what your brain evolved to do for you: to be flexible and learn how to survive, to adapt to a changing environment, and to adapt to the variety of chemicals that you consume. When this situation of “normalcy” is lost because of the absence of something that your brain has become accustomed to having regularly available (e.g., sugar, amphetamine, heroin, or anything else that you are accustomed to consuming), your brain reacts by creating in you the urge to replenish its supply. You experience this feeling as a craving, regardless of the legality, safety, or cost of the substance being craved.
Can I blame it on my parents?
The effects of a drug or your diet on your brain are greatly influenced by your genes, the nature of the drug-taking experience, and the expectations you have about the consequences of the experience. For example, if you respond strongly to one drug, you are likely to respond strongly to many drugs, and p. 46↵this trait is likely shared by at least one of your parents. Many biological factors such as age and weight play a crucial role in the way that food and drugs affect the brain and influence behavior. So, too, does the unique neural circuitry that you inherited from your parents and that neural circuitry sometimes influences whether a drug will be exciting or depressing to you.
This concept is known as the Law of Initial Value. According to this law, each person has an initial level of excitation that is determined by his or her genetics, physiology, sickness or health status, drug history, and environmental factors; the degree of response to a psychoactive drug depends on how all of these factors affect one’s current level of excitation. For example, patients suffering from pain, anxiety, or tension experience euphoria when they are given small doses of morphine. In contrast, a similar dose of morphine given to a happy, pain-free individual often precipitates mild anxiety and fear. If you have a fever, aspirin lowers your body temperature, but aspirin cannot cool your body on a hot day—you must first have the fever for it to work. Coffee produces elation and improves your ability to pay attention if you have been awake for a long period of time or had poor sleep the night before; in contrast, the same dose of coffee is likely to produce much less arousal, or even anxiety, if you are well rested. Catatonic patients may respond with a burst of animation and spontaneity to an intravenous injection of barbiturates, whereas most people would simply fall asleep. Sedative drugs create more anxiety in outgoing, athletic people than they do in introverted intellectual types. Obviously, it can be quite difficult to predict how some drugs or nutrients will affect your brain function. It is not safe to rely upon the experience of others; their physiology and genetic history are likely very different from yours. This principle of brain function is true even for very commonly used, apparently safe drugs, such as caffeine.
p. 47Why am I addicted to caffeine?
Studies have documented that caffeine consumption in young adults directly correlated with increased illicit drug use and generally riskier behaviors; however, these correlational studies never examined the long-term consequences of caffeine consumption. For example, does long-term coffee consumption during adolescence lead to riskier behaviors during adulthood? How might caffeine consumption produce such long-lasting changes? The answers lie in understanding the actions of caffeine in the brain. In adults, caffeine appears to enhance indirectly the activity of dopamine within the brain’s pleasure centers. Drinking coffee produces a mild euphoria due to this effect and encourages the brain to crave more coffee. Yes, coffee is addictive, but only mildly so as compared to many other drugs of abuse such as tobacco and cocaine.
The adolescent brain responds differently to caffeine as compared with the adult brain. For example, caffeine produces a more dramatic increase in motor activity in adolescents. In addition, long-term caffeine consumption produces more tolerance faster in adolescents as compared with adults. This suggests that caffeine might produce greater changes in brain chemistry in the developing adolescent brain. This speculation was strengthened by the finding that long-term caffeine consumption during adolescence leads to greater sensitivity to amphetamine-like drugs that are used to treat attention deficit hyperactivity disorders. Fortunately, there is no current evidence that caffeine consumption leads to attention deficit hyperactivity disorders in children.
A recent study determined that long-term caffeine consumption during adolescence altered the brain’s neurochemistry so that in adulthood the brain’s response to cocaine was enhanced. In contrast, consuming caffeine as an adult does not produce the same type of enhanced response to cocaine. This finding suggests that the developing adolescent brain is vulnerable to the effects of caffeine and that these changes p. 48↵can linger into adulthood and increase the abuse potential of euphoria-producing drugs such as cocaine. Therefore, by definition, coffee and tea are gateway drugs to cocaine. Thus, is caffeine a drug or a food? Sometimes it is very hard to tell the difference.
What should I eat to feel better?
Almost everything you consume may directly or indirectly affect brain function. In order to understand better how food and drugs affect the brain, it will be helpful to divide them into three categories. First, there are chemicals we consume that produce almost immediate effects on brain function, such as those found in coffee, heroin, alcohol, nicotine, marijuana, some spices, and a few psychoactive plants and mushrooms. Their effects depend on how much of the chemical reaches the brain. Sometimes the amount of chemical that actually enters the brain is so low that we do not notice its effects. For example, consider nutmeg: Low doses will be in pies next Thanksgiving, and most of us will not notice that it contains a chemical that our bodies convert into the popular street drug Ecstasy. Yet, if you consume the entire canister of the spice, your intestines will notice (with a terrible diarrhea), and there is a good chance, if the nutmeg is fresh, that you will hallucinate for the next 48 hours. Nutmeg abuse is often popular in prisons.
Second, there are those foods that affect our brain slowly over a period of a few days to many weeks. This is usually called “precursor-loading” and would include many different amino acids (tryptophan and lysine are good examples); carbohydrates that have a high glycemic index such as potatoes, bagels, and rice; fava beans; some minerals (iron and magnesium, in particular); lecithin-containing products such as donuts, eggs, and cakes; chocolate; and the water-soluble vitamins. The purpose of these foods is to bias the function of a specific neurotransmitter system, usually to enhance its p. 49↵function in the brain. For example, scientists once thought that drinking a glass of warm milk before bed or eating a large meal of protein made us drowsy because of tryptophan loading. The current evidence does not support this explanation, but the claim makes my major point: You must get enough of any particular nutrient or chemical to the right place, and at the right dose, in your brain in order for you to notice any effects. In fact, tryptophan has difficulty getting into your brain, particularly when consumed within the context of a large variety of other amino acids, as are present in meat, such as turkey, which, in fact, does not contain very high levels of tryptophan. Pumpkin seeds and egg whites contain far more tryptophan than turkey and no one has claimed that these food sources cause drowsiness. So, what is the scientific evidence for considering the cognitive effects of these foods? Mostly, it is related to what happens when we do not get enough of them. For example, studies have shown that consuming too little tryptophan makes us depressed and angry; historians now blame low-tryptophan diets for multiple wars and acts of cannibalism. Too little of water-soluble vitamins (the B’s and C) in the diet will induce changes in brain function that we will begin to notice after a few weeks of deprivation. Ordinarily, the foods in this second category require more time to affect our brains than do foods in the first category.
The third category includes the slow-acting, lifetime dosing nutrients. This category includes the antioxidant-rich foods such as colorful fruit and vegetables, fish and olive oils, fruit juices, anti-inflammatory plants and drugs such as aspirin, some steroids, cinnamon and some other spices, nicotine, caffeine and chocolate, the fat-soluble vitamins, nuts, legumes, beer, and red wine. People who eat these foods benefit from consuming them regularly over their life span.
The benefit comes from the fact that all of these foods provide our brains with some form of protection against the most deadly thing we expose ourselves to every day—namely, oxygen. Because we consume food, we must consume oxygen. p. 50↵Because we consume oxygen, our tissues suffer the consequences. Thus, people who live the longest tend to eat foods rich in antioxidants or simply eat much less food. Although nicotine and caffeine prevent the toxic actions of oxygen in our brain, this should not be taken as a recommendation to smoke a cigarette with your morning coffee.
We can see here that depending upon how we frame the question about how food affects the brain we end up with a different list of foods and a different reason for consuming them. If you wish to alter your current brain function or slow your brain’s aging, you need to eat specific foods. In truth, no one ever considers these distinctions when eating—most people simply eat what tastes good, and our brains evolved to reward us for eating sugar, fat, and salt. Consequently, food, like any illicit or licit drug, has both negative and positive effects; it all depends on what drug or food you consume and how much you consume.
How do I stop eating so much food?
The real challenge for your brain is how to stop you from eating. This decision is partly determined by how fat you are. The brain learns about this through the action of two hormones—leptin and insulin—and responds by reducing food consumption. The blood levels of insulin and leptin are continuously elevated in the brains of many obese people, but their brains ignore these hormonal signals and so eating continues. The effectiveness of these hormones is influenced by fluctuating levels of estrogen; this leads to the gender dichotomy that females are more sensitive to the appetite-suppressant action of leptin (initiated by their body fat), whereas males are more sensitive to the appetite-suppressant action of insulin (induced by eating). When it comes to food, female brains do not follow the same rules as male brains.
Your brain also gets sensory feedback from your mouth and nose about the smell, taste, and feel of the food, as well p. 51↵as the expansion of the stomach. Unfortunately, these signals can easily be ignored by the brain—and so we keep eating. New research on how the brain gets us to stop eating has led to the development of drugs designed to reduce food intake by mimicking one or more of these feedback signals. But each time the same thing happens—caloric intake decreases for a short time and then the brain adapts to ignore the false signal; ultimately, regular caloric intake is restored. Why? Because the consequences of not ingesting a sufficient number of calories has terrible consequences for your survival. There is no evolutionary advantage to trying to lose weight by restricting eating. Four billion years of evolution have led to the following simple directive for all living things: Find and consume the energy within food, repeat often.
When an energy source is on the tongue, the brain is informed via a series of simple molecular interactions within the taste buds, which lead to the activation of reward pathways in the brain that utilize the neurotransmitters dopamine, endorphins, endocannabinoids, and orexin. Orexin was discovered only recently; it influences both our level of arousal and our craving for food. Take a moment to appreciate how orexin optimizes your daily existence and survival. Orexin-releasing neurons wake you in the morning and then make you crave food. Once food reaches your gut, it encounters still more receptors that detect sweetness, fattiness, and bitterness. It appears as though your entire gut is a continuation of the tongue with specialized taste receptors. The activation of these receptors slows the intestinal transit of the food, providing a greater opportunity for nutrient extraction within the limited length of the intestines.
Is there a good time of day to eat?
What would happen if you could only eat between the hours of 9 a.m. and 4 p.m.? Would you gain less weight and be healthier overall even if you ate a high-fat diet? The answer is yes p. 52↵and is based on how your body is influenced by your daily rhythms of eating and sleeping. There are always negative consequences to ignoring the role of your biorhythms. Many studies have documented that nightshift work, and the odd patterns of sleeping and waking that this lifestyle involves, has many negative health consequences, including insomnia, high blood pressure, obesity, high triglyceride levels, and diabetes—collectively known as the metabolic syndrome. In a recent study, mice were given free access to a nutritionally balanced diet or a diet that was high (61% of their daily calories!) in fat. Some mice were allowed total access to the food at all times; others were only allowed access for an eight-hour window during the early phase of their normal active period. Mice given all-day access to a high-fat diet (which the authors termed the standard American diet) developed obesity, diabetes, metabolic syndrome, and poor sleep-wake rhythms. Now for the good news! The mice that had time-restricted access to the high-fat diet were significantly healthier than the mice given all-day access to the same diet. These lucky mice lost body fat and had normal glucose tolerance, reduced serum cholesterol, improved motor function, and normal sleep cycles. Most surprising, the daily total caloric intake of all groups did not differ, regardless of their diet or feeding schedule.
Therefore, it truly does matter when you eat. The take-home message is eat early, skip dinner, and never have late-night snacks. Skipping breakfast and then overeating in the evening play a significant role in weight gain and obesity. Furthermore, people who skip breakfast report not feeling as satisfied by their food and being hungry between meals. If this sounds like you, then it’s time to change your mealtimes.
What about carbohydrates?
A carbohydrate is a molecule made of carbon, hydrogen, and oxygen. Glucose is a carbohydrate and is commonly called “sugar.” The adult brain has a very high energy demand p. 53↵requiring continuous delivery of glucose from the bloodstream. The brain accounts for approximately 2% of our body weight but consumes approximately 20% of glucose-derived energy, making it the main consumer of glucose. The largest proportion of energy in the brain is consumed by your neurons when they are busy processing incoming sensory information, thinking about complex problems, or contemplating your future. Your brain needs a constant supply of sugar; without it you would quickly lose the ability to think and slip into a coma. We must obtain this sugar from our diet. Somewhere in our evolutionary history, we lost the ability to convert fat into sugar; unlike a few fortunate animals, humans cannot perform this metabolic trick. So, in the morning when you wake up from a long period of fasting, your brain wants you to eat lots of sugar and other simple carbohydrate sources, such as a donut. There is a reason that donuts and sugar-laden cereals are so popular, and you can lay the blame on neurons within the feeding center of your hypothalamus. This mechanism works nicely. First thing in the morning, you eat lots of simple, easily digestible sugars and your brain rewards you with a good feeling by releasing dopamine and endogenous opiates. The amount of dopamine released into your reward center is proportional to how hungry you are; that might explain why you enjoy sugary cereals or a donut for breakfast—they simply taste much better after you have been fasting all night. Your brain needs the sugar to produce chemicals that are critical for learning and memory.
Impaired glucose regulation correlates with impaired learning in the elderly and is associated with Alzheimer’s disease. Scientists recently have discovered that the inability of specific brain regions to use glucose efficiently precedes the degeneration of those same brain region decades later. Eating more sugar is not the answer to preventing dementia. Indeed, consuming large amounts of sugar is not healthy for your pancreas or cardiovascular system. What’s good for the brain is not always good for the other organs of your body.
p. 54What about fats?
We have a fatty brain and fat plays many vital roles in brain function. In the past, very little attention was given to the influence of dietary fats on our mental state. Recent evidence indicates that it might be possible to manipulate our dietary fat intake to treat or prevent disorders of cognitive function. A recent study compared the effects of monounsaturated fats from olive and canola oils with polyunsaturated fats from meat, fish, and vegetable oils on a variety of biochemical changes and electrical properties of cells within a brain region that is critical for learning and memory. After 11 months, a diet high in monounsaturated fats, often referred to as the Mediterranean diet, altered brain chemistry in such a way that learning was enhanced, age-related cognitive decline slowed, and the risk of getting Alzheimer’s disease was reduced. These findings support the addition of canola, olive, and fish oils to our diet and further demonstrate that sensible nutritional choices are vital for optimal brain function and good mental health.
Omega-3 fatty acids are a family of fats that are important components of the human diet. Some recent studies have concluded that being deficient in omega-3 fatty acids may affect brain physiology and increase the risk of cognitive decline. Superficially, this claim makes sense. After all, omega-3 is abundant in the brain and is involved in numerous critical functions. It also may enhance learning and memory processes in the brain. It has been argued that dietary intake of omega-3s, mainly from fish, can slow cognitive decline and the incidence of dementia. These claims may or may not be true. The problem is that the clinical trials related to these claims have either included too few patients or were conducted for quite brief periods of time. Thus, the results were highly variable and potentially misleading. Recently, a study investigating the potential benefit of omega-3s followed almost 3,000 people, aged 60 to 80 years, for 40 months. Their daily diets, medications, and health status were carefully monitored. The p. 55↵patients and their controls were carefully matched for education level, smoking habits, and alcohol use, among other features. The results confirmed that prolonged omega-3 intake (as fish or pill supplement) provides no significant health benefits. Cognitive decline also was unaffected. What does this mean? That a single, good dietary habit, such as high levels of specific essential nutrients, is not enough to provide protection for your aging brain.
In contrast to their lack of benefit for age-related cognitive decline, omega-3 fatty acids may have a beneficial influence on the outcome of depressive disorders. Chronic dietary supplementation with omega-3 fatty acids has produced antidepressant-like effects similar to those of common antidepressant drugs. The therapeutic approach of combining omega-3 fatty acids with low doses of antidepressants might lead to benefits in the treatment of depression, especially among patients with depression resistant to conventional treatments. Such an approach also could decrease the magnitude of some antidepressant dose-dependent side effects.
How does obesity affect brain function and development?
Scientists have demonstrated that obesity leads to hypertension, diabetes, sleep apnea, and numerous arthritic disorders. Obese individuals also perform worse in cognitive tests even when controlled for education level and evidence of depression. Furthermore, women who eat an unhealthy high-fat diet prior to and during pregnancy are more likely to give birth to children, particularly males, who are at risk of abnormal behaviors, predominantly anxiety, during adulthood. Physicians frequently warn pregnant women to monitor their caloric intake and maintain a healthy weight before and during pregnancy. Maternal nutritional status, infection, and physical or psychological trauma during pregnancy can all increase the risk of obesity, diabetes, and mental disorders in offspring. In the past, the concern was maternal malnutrition—that is, the p. 56↵developing fetus might lack critical nutrients for normal growth. Today, in the United States, the concern has shifted to overnutrition and obesity and the risks faced by the developing fetal brain. Maternal obesity leads to serious inattention problems in offspring and a twofold increase in the incidence of impaired emotional regulation that was still evident five years after birth. Maternal obesity also causes abnormalities in areas of the brain responsible for feeding behavior and memory. All of these changes were most noticeable in male offspring. How does maternal obesity impair fetal brain development? Once again, the damage is due to the fact that fat cells release inflammatory proteins, called cytokines, into the body and brain of both mother and fetus. The more fat cells the mother has, the more cytokines get released into her blood. As discussed earlier, the presence of these cytokines increases the likelihood of becoming depressed. Exercise can modestly reduce the level of cytokines in the brain, and if overweight, moms might find some relief from their depression by exercising.
Why do I like to eat?
Two different neurotransmitter systems, endogenous opioid peptides called endorphins and cannabinoids, make eating pleasurable. Endorphins enhance the sensory pleasure derived from food, and the consumption of foods high in fat and sugar stimulates the release of endorphins. Endorphins enable us to experience the deliciousness of food and ensure that we do not stop eating too soon; endorphins do not influence our decision to eat. Drugs that selectively block the action of endorphins reduce the intake of foods that are quite sweet or have a high fat content. Interestingly, these drugs that block endorphins only reduce the pleasure of eating these foods; they do not reduce the feelings of hunger.
Endorphins drive us to overconsume palatable foods by blunting the impact of feeling full. As we all know, while standing next to the buffet table we will engage in mindless p. 57↵eating. We know that we should stop eating and move away from the buffet line and let someone else get at the food. Our bellies are full to the point that it hurts to breathe. Belts are loosened another notch. So why can’t we stop eating? Neuroscientists have some interesting explanations. One of these is called “ingestion analgesia,” and it involves endorphins. The function of ingestion analgesia is to keep you eating. Even though continued eating has become unpleasant because the stomach is painfully stretched to its full capacity, we still keep eating. Essentially, we block out the painful feedback from these feelings by releasing endogenous opiates into our brain and body. Not surprisingly, our reaction to pain is reduced significantly when eating tasty foods, such as cheesecake or rich chocolate. This explains why we can indulge in a decadent dessert even after we have become fully satiated by a large meal. We have basically become insensitive to the pain of continued eating. Also, if the animal eating next to you tries to take away your portion of the food, having your body flooded with endorphins will lessen the pain of any injuries that you sustain.
Brains evolved when food was scarce; thus, we are compelled by our genetic legacy to eat whatever and whenever possible until everything that can be consumed, is consumed to completion. All animals have a tendency to eat a great deal of food when palatable food is readily available. Not only that, but we also subconsciously prevent others from taking our food source. Just watch people’s body posture at a buffet table. We defend our access to tasty food when it is within easy reach and is at risk of being consumed by other humans. Studies have shown that humans will eat more when more food is available even when the food is stale or otherwise unappealing (which is good news for bad cooks!). Furthermore, even if you point out to someone that the food is stale or that he has eaten more than his fair share, he will continue to eat. Our biological drive to consume tasty foods to completion outweighs any opposing cognitive or motivational factors.
p. 58↵Even after you have gained a lot of weight, your brain wants you to gain more. Research indicates that obese humans have elevated levels of endogenous endocannabinoids—marijuana-like chemicals—in the blood and brain. Remember “the munchies?” When we become overweight, our bodies induce a constant state of the munchies by bathing our brain in endocannabinoids. The endogenous marijuana neurotransmitters, the endocannabinoids, also contribute to the pleasure of eating. Scientists have discovered that marijuana increases the pleasurable response to eating sugar but has no effect on how much we dislike the taste of other types of foods. For example, if you hate eating peas or broccoli, smoking marijuana will not induce you to like eating them.
The ability of sugar to induce a rewarding feeling is caused by the release of dopamine in the brain’s reward center. This brain region informs you that your brain likes this food and wants you to consume it more often. In the presence of marijuana, significantly more dopamine is released in response to the same amount of sugar-enriched food. So what does all of this mean? Your brain’s endogenous marijuana system ordinarily modulates how good a particular food tastes; smoking marijuana simply enhances this natural mechanism in the brain. Your brain’s main purpose is to help you survive and pass on your be-fearful-first genes. Eating is a critical and necessary behavior that the brain organizes and controls to allow daily survival. Therefore, the brain rewards itself for successfully consuming enough calories to survive by releasing these two powerful neurotransmitters—endorphins and endocannabinoids. Because of the manner in which evolution has shaped the response of our brain to food, overeating of calorie-dense foods has become a major health problem in the modern world. Our brains were shaped by evolution to be very efficient at instructing us to eat, but quite inefficient at stopping us from eating.
p. 59Why do I crave fat and sugar?
Fat and sugar are craved like heroin or methamphetamine. Why is this so? The answer is that these foods actually change how the brain functions. Day after day, year after year, the constant bathing of the brain in fats and sugar slowly changes how the neurons within our brain’s feeding center behave. Along with these changes, gradual modifications in brain circuitry also occur; ultimately, your brain rewires itself to eat more fat and sugar every day in order to feed the ever-more-powerful new programing that is evolving inside your brain. Scientists once assumed that obese people were simply addicted to food in the same manner that someone becomes addicted to heroin—that is, food produces happy, pleasant feelings, and, therefore, eating lots of food would produce extremely pleasant feelings. Not so. A few years ago scientists discovered just the opposite was true: The brain’s reward center decreased its response to eating tasty foods. In obese humans, dopamine function becomes significantly impaired in response to many years of poor diet. Consequently, obese people consume ever greater quantities of fat and sugar in order to mitigate the diminished rewards that were once experienced by consuming only one scoop of ice cream or a small donut.
Are we born destined to become obese?
For some people, apparently, the answer is yes. Environment, determined by both geographical and societal forces, plays an important role. The genes we inherit from our parents also play a role. Many studies have shown that children who have two obese or overweight parents are four times more likely to become obese themselves. To be considered low risk, the parents of the adolescents needed to be lean, with a body mass index less than 25. When the children in the high-risk group were shown pictures of tasty-looking, high-calorie foods, the dopamine-dependent pleasure centers in their brains became p. 60↵highly activated, especially as compared with the response of the same brain regions in the low-risk children. Some children who are destined to become obese apparently inherit a dopamine system that becomes much more excited at the sight of a chocolate milkshake than does the dopamine system in the brain of a child who is not destined to become obese as an adult. Then, in adulthood, the brain switches the rules and begins to require more fat, salt, and sugar in order to achieve a similar level of dopamine-mediated reward. Once again, take note of the fact that your brain has only one goal: keep you alive long enough to pass on your genes to your offspring. Once that has happened the forces of evolution no longer care about your survival. Thus, your brain will regularly induce you to consume foods that bring it pleasure regardless of the long-term health consequences.
How do my gut bugs keep my brain healthy?
Your brain lives in a symbiotic relationship with the bugs in your gut. Whatever you eat, they eat. In return, they help your brain function optimally in a variety of ways. During the past few years, it has become increasingly apparent that in the absence of bacteria humans never would have evolved to our current level of cognitive performance. Our brains are profoundly dependent upon a wide range of chemicals produced by these gut bugs. For example, without these gut microbes our brains do not correctly develop the serotonin neurons that play a key role in the control of emotion.
If you were to count all of the cells on and inside of you that are not actually you, they would number in the trillions. These bugs were not simply along for the ride as we became the dominant species on this planet; they made the journey possible. As soon as individual cells evolved into fully multicellular organisms during the Cambrian period about 500 million years ago, they quickly discovered the fantastic survival benefits of fully integrating themselves; once there, they never left. The total p. 61↵weight of the many trillions of bugs that reside in your gut is over two pounds and they are multiplying constantly thanks to all of the nutrients you are providing them; they are also in a constant battle for survival. The viruses in your gut kill so many bacteria every minute that their carcasses account for about 60% of the dry mass of your feces (now you know what is in there!).
Gut bacteria produce many different chemicals that can influence brain function. They convert the complex carbohydrates in our diet to the fatty acids butyrate, acetate, and propionate. Butyrate can easily leave the gut and enter the brain, where it can influence the levels of brain-derived neurotrophic factor (BDNF). BDNF plays a critical role in the birth and survival of neurons and the ability of the brain to learn and remember. Reduced levels of BDNF are correlated with impaired cognitive function and depression. Accumulating evidence suggests that gut bugs play key roles in both the developing and mature nervous system and may contribute to emotional and behavioral disorders as well as numerous neurodegenerative diseases.
Recent animal studies have shown that eating a high-fat diet can negatively alter the diversity of your gut microbiome, leading to reduced plasticity in the brain and increased vulnerability to anxiety. Eating a diet high in sugar also altered microbial diversity and significantly impaired learning and memory abilities.
Obviously, you need to take good care of these bugs so that they will take good care of your brain. Consuming prebiotics and probiotics can help us to maintain a healthy diversity within the bug environment. For example, elderly and frail humans who have major cognitive impairments also have the lowest level of bug diversity in their guts.
Can a good diet make you smarter?
Given that a poor diet can impair cognitive function, can a good diet make you smarter? Recently, a group of scientists p. 62↵investigated whether eating fruits and vegetables for 13 years would actually protect against a decline in cognitive abilities that humans commonly experience with normal aging. Their answer? Yes, it does; this is how they proved it. The study involved about 2,500 subjects who finished the study and adequately completed all the dietary and cognitive evaluations. The subjects were between 45 and 60 years of age at the beginning of the 13-year study, and they were required to maintain careful and detailed records of their daily diets. The subjects were evaluated at the beginning and end of the study for a variety of cognitive abilities, including verbal memory and higher executive functions such as decision-making and mental flexibility, along with numerous other tests. There is good news and bad news in the results. First, their diets were composed of a variety of fruits and vegetables, but specifically excluded potatoes, legumes, and dried fruits (each of these foods would have introduced specific complications that might have interfered with the outcome). The adults were divided into four groups according to the following diets: folate-rich diets containing fruits and vegetables, beta-carotene-rich diets containing fruits and vegetables, vitamin C-rich diets of fruits and vegetables, and vitamin E-rich diets containing both fruits and vegetables. The individual consumption of specific nutrients—folate, beta-carotene, and vitamins C and E—also was monitored. The subjects were allowed to choose how much of each diet they wished to consume each day; therefore, daily intakes of each nutrient varied. This was allowed in order to more closely reproduce how most of us actually select our daily intakes. At the end of the study, this is what they found. Eating fruits and vegetables has significant beneficial effects on very limited aspects of brain function. When the specific diets were examined more closely, diets that consisted of only fruits or diets with fruits and vegetables rich in vitamins C and E selectively benefited only verbal memory scores. This test involved being told to remember 48 different words and then recalling them after a delay with distractions. p. 63↵The surprising finding was that eating fruits and vegetables had no significant benefit for other types of tasks that required alternative types of memory, such as learning motor tasks or recognizing familiar objects.
Clearly, each component of your diet may influence how well your brain works in unique ways. Natural antioxidants found in fruits and vegetables, like polyphenols, provide protective effects for the brain through a variety of biological actions. Polyphenols are everywhere in nature; more than 50 different plant species and over 8,000 such compounds have been identified in plant extracts. Obviously, investigating the multiple health benefits of these natural chemicals poses an enormous challenge. The most thoroughly investigated polyphenols are probably quercetin, which is found in apples, tea, and onions, and resveratrol, which is found in the skin of grapes. Grapes use resveratrol to defend against fungus. Tea contains a number of beneficial chemicals. In neurodegenerative diseases, administration of tea extracts reduced the production of mutant proteins and may prevent neuron cell death in Alzheimer’s disease. Although tea is not a cure for Alzheimer’s disease, its use is certainly justified given its safety and potential for long-term benefits.
What about an apple a day?
Are fruits good for you? After all, most fruits are full of sugar. Many popular diets recommend avoiding carbohydrates, especially sugar, in any form. There are some good arguments that could be made about avoiding sugar, but if this approach takes fruits out of your diet, you may be missing important nutrients that might make you healthier in the long term. One of these important nutrients is ursolic acid. Ursolic acid is found in apples (mostly in the skin), cranberries, and prunes, as well as in elderflower, basil, bilberries, peppermint, rosemary, thyme, and oregano. Eating fruits and spices that contain ursolic acid may enhance brain function and reverse some of the negative p. 64↵effects of obesity on the brain as you get older. Studies have shown that ursolic acid can improve cognitive functioning by increasing your brain and body’s sensitivity to insulin. The biological mechanisms now have been investigated fairly well, and it appears that ursolic acid is able to correct some of the errors of metabolism induced by long-term obesity. The real challenge is to discover how many apples, prunes, and cranberries you need to eat in order to achieve these benefits; studies on humans have never been performed.
Will you lose weight by eating these fruits?
Maybe; it depends on what else you are eating. Will you lose weight avoiding fruits and berries while only eating meat? Yes. Over the long term, however, it is unwise to do so. The benefits of an all-meat diet are more immediate than the benefits of eating apples, cranberries, and prunes, because their effects on your health take longer to notice. Essentially, most of the restriction diets that are often promoted in popular magazines have not been around long enough for medical science to determine the long-term risks. Dietary restriction, which is reduced caloric intake without essential nutrient deficiency (i.e., a state of undernutrition without malnutrition), is the only valid, scientifically proven dietary intervention that has been shown to slow the aging process and improve health. There are two reasons why we hear so little about this approach: First, no one stands to profit from all of us eating less food and more apples, cranberries, and prunes. Second, the effects of dietary restriction on longevity have never been demonstrated in humans because rigorous and well-controlled clinical investigations have never been attempted. The effects of dietary restriction on health and longevity have been compellingly demonstrated across numerous species from single-cell organisms to rats to primates. If you are not willing to restrict your calorie intake, some alternatives are discussed in the following paragraphs.
p. 65Are spices good for my brain?
Cinnamon is a spice obtained from the bark of the Cinnamomum verum tree. Since antiquity, it has had many uses. Moses included it as an ingredient of the holy anointing oil. The Chinese knew it as Gui Zhi and recommended it for its antibacterial and antipyretic properties. Medieval physicians included cinnamon in their preparations to treat arthritis and infections. (The widespread use of willow tree bark [and the aspirin-like chemical that was derived from it] for these ailments was still a thousand years in the future.) A recent study found that eating cinnamon might prevent a variety of age-related neurological disorders. How does this happen? The sodium benzoate produced in the body after eating cinnamon induces significant increases in the levels of a variety of chemicals in the brain called neurotrophic factors. These factors stimulate the birth of new neurons in the brain and encourage the survival of existing neurons. These two processes are critical for the maintenance of a healthy brain. During the past decade, many scientific studies have discovered that these neurotrophic factors can prevent, or greatly slow, the progression of a variety of degenerative diseases of the brain, including Alzheimer’s and Parkinson’s disease. Cinnamon also can reduce blood sugar levels slightly in people with type II diabetes and reduce cholesterol levels by up to 25%. Thus, cinnamon is good for your brain and body.
Curcumin, derived from the spice turmeric, the powdered rhizome of the medicinal plant Curcuma longa, has been used for many centuries throughout Asia and India as a food additive and a traditional herbal remedy. Studies have shown that curcumin has potent antioxidative and anti-inflammatory proclivities that may be beneficial for patients with Alzheimer’s or Parkinson’s disease. Treatments with natural antioxidants and anti-inflammatories through diet or dietary supplements are becoming attractive alternatives. Epidemiological and research findings strongly indicate that the solution to healthy p. 66↵aging is exactly what you have heard from your mom: Eat healthy and in moderation; exercise in moderation.
Let food be thy medicine and medicine be thy food.
—Hippocrates (460–370 b.c.e.)
During the past 2,500 years since the time of Hippocrates, science has made significant progress in understanding how food exerts its beneficial effects on health. We now have solid proof that the foods and beverages that are consumed by humans, in particular those derived from tea leaves, coffee and cocoa beans, celery, grapes, mangos, berries, hops, and other grains, have clearly defined beneficial effects on brain function. Although these foods and drinks have quite different chemical compositions, they all contain compounds called flavonoids. Flavonoids are not in themselves nutritious, but they are believed to be responsible for the beneficial effects of many foods on the brain.
How do flavonoids benefit us?
In order to answer this question, scientists have investigated what flavonoids can do when their concentration in the brain is extremely low, that is, at levels that are likely achieved by a diet rich in these fruits. The flavonoids directly induce neurons in the brain to become more “plastic”—that is, more capable of forming new memories. The flavonoids achieve this by directly interacting with specific proteins and enzymes that are critical for learning and memory. They also induce the birth of new neurons, a process that is critical for recovery from injury, exposure to toxins, and the consequences of advanced age, such as increased levels of brain inflammation. Finally, some recent studies have shown that flavonoids actually enhance blood flow to active brain regions and thereby allow enhanced neuronal function.
So how much is enough? Let us consider two of our common favorites: wine and chocolate. If you consumed about p. 67↵200 milliliters (6.7 ounces) of Cabernet Sauvignon or about 50 grams (1.7 ounces) of dark chocolate (71% cocoa powder), you would take in nearly identical quantities of flavonoids, which, fortunately, is now the daily wine intake recommended to produce the most health benefits in a typical adult. When young adult females were given flavonoid-rich chocolate drinks, blood flow to their brains significantly increased within just two hours, and their performance on a complex mental task greatly improved. No one is certain whether all flavonoids are capable of producing these benefits. Recent investigations have suggested that it does not matter which type of food provides the flavonoids, only that you should eat them as often as possible. In addition to those edibles mentioned above, studies to date also have identified benefits from black currants, pears, blueberries, strawberries, and grapefruit. You might have noticed that all of these healthy choices are darkly colored—their color is what makes them so valuable to your body. One final caveat: No studies have yet proven a true cause-and-effect connection between the lifelong consumption of flavonoid-rich diets and a reversal of age-related deterioration in learning or general mental function. Still, just in case, it might be worth modifying your diet accordingly (e.g., eating more chocolate).
In 1648, according to the diary of English Jesuit Thomas Gage, the women of Chiapas Real arranged for the murder of a certain bishop who forbade them to drink chocolate during mass. In an ironic twist, the bishop was ultimately found murdered after someone had added poison to his daily cup of chocolate. Was this an act of blind rage by the women of Chiapas Real or justifiable homicide? For a small percentage of the population, eating chocolate can produce rage, paranoia, and anger that occur without warning. Fortunately, for most of us, this is not the typical reaction to eating chocolate. In order to understand p. 68↵why chocolate is so enjoyable for some while it induces uncontrollable rage in others, we need to consider the contents of most dark chocolates. Chocolate contains an array of compounds that contribute to the pleasurable sensation of eating it. Many of these compounds are quite psychoactive if they are able to get into our brains. Are they the reason we love chocolate so much? Are they the reason some people fly into fits of anger? The answer to both questions is, of course, yes. However, as is true for so many of the things we eat that affect our brain, it is not all that simple.
Chocolate usually contains fats that may induce the release of endogenous molecules that act similarly to heroin and produce a feeling of euphoria. German researchers reported that drugs that are able to block the actions of this opiate-like chemical produced by eating chocolate prevented the pleasure associated with eating chocolate. Chocolate also contains a small amount of the marijuana-like neurotransmitter called anandamide. Although this molecule can easily enter the brain, the levels in chocolate are probably too low to produce an effect on our mood by themselves. Chocolate contains some estrogen-like compounds, a fact that may explain a recent series of reports showing that men who eat chocolate live longer than men who do not eat chocolate. (The effect was not seen for women, who have an ample supply of their own estrogen until menopause.)
Let us focus on those women of Chiapas Real again. In contrast to its effects on men, women more often claim that chocolate can lift their spirits. In a study of college students and their parents, 14% of sons and fathers and 33% of daughters and mothers met the standard of being substantially addicted to chocolate. Women seem to have very strong cravings for chocolate just prior to and during their menstrual cycle. Women eat more chocolate in the days before the start of their period when progesterone levels are low. This is when premenstrual symptoms tend to appear as well. Chocolate may provide an antidepressant effect during this period. In p. 69↵one study, researchers found that women in their fifties often develop a sudden strong craving for chocolate. It turns out that most of the women had just entered menopause and were on a standard form of estrogen replacement therapy consisting of 20 days of estrogen and 10 days of progesterone. The chocolate cravings developed during the days on progesterone.
Chocolate contains magnesium salts, the absence of which in elderly females may be responsible for the common postmenopausal condition known as “chocoholism.” About 100 milligrams of magnesium salt is sufficient to take away any trace of chocoholism in these women, but who would want to do that? Finally, a standard bar of chocolate contains as many antioxidants as a glass of red wine. Clearly, there are many good reasons for men and women to eat chocolate to obtain its indescribably soothing, mellow, and yet euphoric effect.
Okay, what about the anger? How might that happen? Chocolate contains phenethylamine (PEA), a molecule that resembles amphetamine and some of the other psychoactive stimulants. When chocolate is eaten, PEA is rapidly metabolized by the enzyme monoamine oxidase (MAO). Fifty percent of the PEA you consume in a chocolate bar is metabolized within only 10 minutes. Therefore, very little PEA usually reaches the brain, thus contributing little or no appreciable psychoactive effect. However, the amount of PEA in the brain might reach noticeable levels if MAO levels are low. Thus, it might not be a coincidence that MAO levels are at their lowest level in premenstrual women when they most crave the soothing effects of chocolate.
Chocolate also contains small amounts of the amino acid tyramine. Tyramine can powerfully induce the release of adrenaline, increase blood pressure and heart rate, and produce nausea and headaches. Usually, the nasty effects of tyramine are prevented because MAO metabolizes it, too. You can see the problem: The tyramine and PEA in chocolate may slow each other’s metabolism. The consequence is that if both of these chemicals hang around too long in the body, high blood p. 70↵pressure, a fast-beating heart, heightened arousal, racing thoughts, anger, anxiety, and rage would ensue. One rather controversial study claimed that inhibitors of MAO were able to increase PEA levels in the brain 1,000-fold! That is a lot, and the consequences of this actually happening could be lethal. Nevertheless, the potential exists for some vulnerable people to experience significant shifts in mood after eating chocolate with high cocoa powder levels.
The main point to take away from this discussion about chocolate is that plants, such as the pods from the cocoa tree, contain a complex variety of chemicals that, when considered individually, are not likely to impact our brain function. When considered in aggregate, however, they may exert compound effects throughout the body; some of those effects may be desirable, while others may not. Chocolate is yet another excellent example of how difficult it is to differentiate food from drugs.
Brain toxins in the diet
Foods are full of toxins and nutrients; however, this is only from our human perspective, not the plants’ perspective. The overwhelming percentage of toxic substances we consume exist naturally in the plants we consume. Indeed, most of the chemicals humans consider nutritious occur in the same parts of the plants that we consider toxic. Toxins and nutrients are byproducts of the plant living its plant life. We evolved the ability to defend ourselves from these toxins as long as the levels were not too high. Plants absorb lots of different molecules from the land in which they are growing. Some of these can interact with our brain. One famous example is aluminum. Aluminum is everywhere around us all of the time. It is the most abundant metal in the Earth’s crust. Yet, somehow, we have become fearful of it when it is used as cookware, as cans for beer or sodas, or as deodorants. As far as anyone can currently determine, no plants or animals need it for any biological p. 71↵purpose. The reason is that aluminum is highly reactive and easily combines with other metals and oxygen to form hundreds of different minerals. Aluminum, in scientific terms, is not bioavailable to humans—usually. It all depends upon what chemical form the aluminum takes on. Usually, because aluminum is so tightly bound within minerals, animals have no chance to absorb it into their tissues.
This all changed a century ago due to the burning of certain types of coal for energy. In addition, anyone over a certain age will remember the fears associated with acid rain. Although the consequences of having elevated levels of sulfur dioxide and nitrogen oxides in the air have been known since the beginning of the Industrial Revolution, public awareness peaked in the 1970s due to the appearance of “dead lakes,” the destruction of entire forests, and the pitting of marble statues in the United Kingdom and Europe. A century of acidic rains settled into the soil and changed the chemistry of minerals containing aluminum.
Plants do not use aluminum, but they are capable of absorbing it from the soil. Grains that are harvested today to make breads and cereals often contain a few parts per million of aluminum. However, the aluminum in grains unfortunately exists within a bioavailable form, that is, a chemical form that we humans can absorb into our bodies and deposit in tissues. Animals who eat these plants concentrate the aluminum in their tissues, too. Thus, meats obtained from cows may contain up to 1,000 parts per million of aluminum. This is where things get a little dicey. Are we at risk from the aluminum in our diet? As was true for drugs, it depends entirely upon how much one consumes.
Some people are vulnerable to the presence of aluminum in the body. For example, a few years ago people undergoing dialysis began using water containing high levels of aluminum. Over time the levels of aluminum in their brains and bodies began to increase and produced changes in their behavior that resembled dementia. The aluminum deposited p. 72↵within some brain cells caused those cells to die. Fortunately, dialysis centers are aware of this risk and have taken steps to prevent the problem from occurring again. Aluminum does not cause Alzheimer’s disease, although it has been found in the brains of patients who have died with Alzheimer’s disease. Although this seems suspicious, aluminum salts will deposit in any soft tissue that has cell loss due to injury or degeneration. For example, aluminum salts also will accumulate in the hearts of people with coronary disease.
What about deodorants? The aluminum salts used in these products do one thing—they irritate our sweat glands to the point that they swell and close the pores that allow perspiration to reach the surface of our skin. Essentially, aluminum prevents its own absorption by doing so. The real risk from deodorants comes from using sprays that produce a cloud of aluminum salts that can be inadvertently inhaled. Thus, keep using your aluminum cookware—it poses no risk to health.