The following is Reason No. 3 from my book Top Ten Reasons We’re Fat: And What to Do About It, available at Amazon.
Not long ago, and to some extent even now, some people, both experts and laypersons, thought that people may be disposed to weight gain because of mental health issues. If one is depressed, for example, one might eat “comfort food”, which is usually something very tasty, loaded with sugar and/or crunchy and “carby”, in order to allay the nagging feelings of that illness and improve one’s mood. (That’s the hope anyway; usually, as with alcohol, the fix is merely temporary.). Similarly, if a person has some other type of mental derangement, he or she may not care much about weight gain, as they may have little future time orientation and prefer the “now” of eating to the future of having a trim physique. To lose weight, deferred gratification, even eternally deferred, makes a big difference.
Obesity and Mental Health
Indeed an association of depression with obesity exists. In one prospective study, adolescents who were depressed were more likely later to become obese. The same association, depression to obesity, has been found elsewhere, in other populations, too, and it’s also been found that the obese are more likely to become depressed, that is, the association between obesity and depression is “bidirectional”. This still doesn’t mean that depression causes obesity, as there may be some third factor that links both together, inflammation perhaps, or genetics. But the link is a solid one that has been confirmed by many studies, with morbidly obese people having a many-fold higher incidence of depression. Unlike with other epidemiological studies, the link between depression at a starting time point and depression later appears to show more than mere association; it points to something more akin to causality.
While all this is true, plenty of people with perfectly normal mental health have become overweight and obese; indeed, lots of people who are very health conscious and have done all the things the experts tell them to do have also become obese. So the mental health model, then, doesn’t begin to cover the whys and wherefores of being too fat. One of the themes of this book is how following the conventional diet and exercise advice has made so many people fat.
Obesity, Food, and Evolution
However, there is another sense in which the brain is involved in obesity, and we owe this to our evolutionary development. Human beings have existed in more or less their present form for one million years or more. In all that time, they have evolved in an environment vastly different from the one they live in now, an environment to which our brains, guts, and the rest of our bodies evolved to be adapted. If we change our environment, without enough time to allow for evolution to work its magic, it follows that we may very well be maladapted to our current environment.
Consider that humans and other animals must have food to survive. Natural selection has ensured that we have physiological mechanisms that give us the drive to obtain that food. One such physiological mechanism is hunger; if this goes on long enough it becomes such a strong urge that the drive to find something to eat will supplant every other drive and emotion. We may become willing to commit a crime in order to obtain food, and in countries that are ravaged by war or famine, people have often been willing to do much worse than that. Hunger is powerful. Yet most people in the modern world have probably never really felt hunger in the sense of that all-powerful urge. We are now always within reach of food; few of us have gone days without being able to eat.
Food tastes better when we’re hungry; an old proverb has it that “hunger is the best sauce”. Good-tasting food also gives us pleasure, which is another mechanism that gives us the drive to eat. Bitter, nasty tastes are often a sign that we should not be eating this thing that tastes like that, and we recognize this by the displeasure that we feel. Taste feels like it’s on the tongue, but as with other pleasures and displeasures, it’s our brain that produces these sensations. When we taste something good, neurons are firing their neurotransmitters across the synapses, communicating with each other. The fact that we feel pleasure when eating ensures that we won’t go long before eating again. Evolution uses the sensation of pleasure as motivation for many things that promote our survival and reproduction, sex being a very notable example. If people needed logic and rationality rather than pleasure to reproduce, humans would have died out ages ago, and much the same could be said about food. Satisfying the sexual urge and satisfying hunger are both pleasurable, and the fact that food gives us pleasure is part of what drives us to eat.
Another category of substances besides food that produce a pleasurable effect on us that is mediated by our brains is that of certain psychoactive drugs. These however usually do not enhance our survival and reproduction, with the possible exception of opiate painkillers. (Well, sometimes alcohol may increase the odds of success in our attempts at reproduction, but that’s another story altogether.) Psychoactive drugs do, however, use the same brain circuits that produce pleasurable sensations. These brain circuits were originally put in place by natural selection for other purposes. For example, we have opioid receptors in our nervous system, as well as opioid chemicals, called endorphins. Opium and its derivatives, such as morphine and heroin, bind directly to those receptors, producing a sense of pleasure. The same can be said of other drugs; for instance, the brain has cannabinoid receptors to which the active ingredient of cannabis binds, and it even has benzodiazepine receptors, to which Valium and similar drugs attach to. (There are some exceptions; there’s no alcohol receptor, for instance.) Drugs essentially short-circuit inborn biochemical pathways.
Food, Drugs, and Addiction
The brain is plastic however, that is, it can change how it acts and responds to certain repeated stimuli. For example, if repeated administrations of certain drugs that bind to receptors are given, more receptors are made. This is at least in part the basis of addiction: since more receptors are made, the same dose of drug that was originally enough to produce the required effect becomes less effective, and in fact, the user of addictive drugs may find after some time that he needs the drugs just to feel normal. Even SSRIs, a popular class of antidepressant, seem to act in this way.
So what does this discussion of drugs and addiction have to do with being fat? Well, some foods seem to have the property of being addictive. They produce pleasure by stimulating parts of the brain, and the person who eats that food comes to want more of it, and may come to need it to feel normal
A recent review paper on addiction, “Molecular basis of long-term plasticity underlying addiction”, discusses these brain changes. From the abstract to the paper:
Studies of human addicts and behavioural studies in rodent models of addiction indicate that key behavioural abnormalities associated with addiction are extremely long lived. So, chronic drug exposure causes stable changes in the brain at the molecular and cellular levels that underlie these behavioural abnormalities. There has been considerable progress in identifying the mechanisms that contribute to long-lived neural and behavioural plasticity related to addiction, including drug-induced changes in gene transcription, in RNA and protein processing, and in synaptic structure. Although the specific changes identified so far are not sufficiently long lasting to account for the nearly permanent changes in behaviour associated with addiction, recent work has pointed to the types of mechanism that could be involved.
Can food do the same? Can it change our brains in such a way that we become addicted? It appears that it can. Another recent review directly compared food to addictive drugs:
Recent work on food use disorders has demonstrated that the same neurobiological pathways that are implicated in drug abuse also modulate food consumption, and that the body’s regulation of food intake involves a complex set of peripheral and central signaling networks. Moreover, new research indicates that rats can become addicted to certain foods, that men and women may respond differently to external food cues, and that the intrauterine environment may significantly impact a child’s subsequent risk of developing obesity, diabetes, and hypercholesterolemia.
It’s been found in rats that consumption of sucrose (table sugar) causes an increase in the amount of delta fosB, which is a marker for the brain changes associated with addiction. Rats also can show signs of withdrawal when they no longer have access to their accustomed, addictive foods.
When a group of rats were allowed to choose between cocaine and saccharin-flavored water, 94% of them preferred the saccharine, showing just how powerful a sweet taste is. (The researchers used saccharine so that both the cocaine and sweet-tasting water were calorie-free.) The authors of this study write, “Our findings clearly demonstrate that intense sweetness can surpass cocaine reward, even in drug-sensitized and -addicted individuals. We speculate that the addictive potential of intense sweetness results from an inborn hypersensitivity to sweet tastants. In most mammals, including rats and humans, sweet receptors evolved in ancestral environments poor in sugars and are thus not adapted to high concentrations of sweet tastants. The supranormal stimulation of these receptors by sugar-rich diets, such as those now widely available in modern societies, would generate a supranormal reward signal in the brain, with the potential to override self-control mechanisms and thus to lead to addiction.”
If you eat a lot of sugar-sweetened foods, and have trouble refraining from eating them, especially to the point where they are causing you to be overweight, you just might have an addiction problem.
The type of foods that are potentially addictive are known as highly palatable foods, that is, they simply taste very good, and as such they set off the reward circuits of the brain. Highly palatable foods, like addictive drugs, can be said to hijack some of the brain’s circuitry that was originally meant for other purposes. For example we have taste buds that respond highly to sugar, indicating that sugar was favorable to our survival and reproduction in our so-called environment of evolutionary adaptation (EEA). However, in our EEA, sugar was not abundant, being present only in ripe fruit and honey. Table sugar did not exist. But now that it does exist, it highjacks our normal circuitry, and can produce changes indicative of addiction. This is similar to the example of opiates, which, becoming available in the environment, use our endogenous opioid brain circuits, producing addiction.
The Concept of the Supernormal Stimulus
These modern foods that have addictive potential are sometimes said to be supernormal stimuli. This phenomenon was discovered by the Nobel laureate Niko Tinbergen. He found, among other things, that birds will respond more to artificial eggs that were larger and brighter than their own eggs. In the presence of these artificial eggs, birds would neglect their own eggs and nurture the artificial ones. This phenomenon has been found to extend to many biological functions and behaviors of many animals. For example, certain male fish will attack wooden objects made to resemble others of their kind much more strongly than they will attack actual male fish. In humans, artificial, augmented breasts have been rated more attractive than real breasts, regardless of size, and this has been deemed an example of a supernormal stimulus.
Certain kinds of food are obviously supernormal stimuli, artificially created, designed to appeal to senses that evolved in an era when these foods were unavailable. Like augmented breasts, we consider them more attractive (tasty) than real food, and we gravitate toward them, driven by our evolved instincts. As artificially augmented breasts are deceptive signs of fertility, which is why we are attracted to them, artificially made food – what I like to call industrial food – are deceptive signs of nutrition. If we follow either signal, our evolved drives lead us astray. As it clearly makes no sense from the standpoint of reproduction to be enamored of fake breasts, it doesn’t make sense from the standpoint of supplying our bodies with what they need to be enamored of fake food. Disruption of our evolved biology follows in both cases.
Food, when considered as a supernormal stimulus, can cause an alteration of behavior in humans. We will respond to food that tastes supremely great by wanting more of it and possible becoming addicted to it. It can make us overweight and obese.
There are a number of types of food that can do this. Those containing sugar are perhaps preeminent among them. Most or even all of them that can act this way are processed foods that did not exist in our ancestral environment, and our brains have not evolved to deal with them, and respond in maladaptive ways. Besides sugar, salt and fat are the ingredients most likely to be present in addictive food.
The Food Industry and Highly Palatable Food
Food manufacturers have systematically developed foods that appeal mightily to our taste buds. And why wouldn’t they? They want us to buy their food, and if we become addicted, so much the better for them. The old slogan for a certain brand of potato chips said, “Bet you can’t eat just one.” When we do eat one, we immediately want another.
Some foods with the potential for addiction include donuts and other pastries and cakes, ice cream, cookies, potato chips, chocolate, french fries, and candy. As can be seen, paleolithic man had access to none of these. We are not adapted to them, yet we love them.
All that being said, there are skeptics of the idea of food addiction. For one thing, unlike the case with addictive drugs, we require food to survive. For another, probably most of the people who eat these foods do not become addicted to them. However, perhaps less than 10% of users of alcohol become addicted to it, but we would not for that reason say that alcohol is not addictive. It seems at least possible that the same holds for certain types of food: some subset of the population will become addicted to them.
If you eat compulsively, especially of the kind of foods mentioned above, it may be possible that you are addicted to them. The way around this is simple and yet for some, difficult, namely don’t go near these foods. As with alcohol, it may be that for some people, total abstinence is the only way to go.
If you think you have this problem, eat foods that are not made by the food industry. Buy meat, eggs, dairy, fruits, vegetables, and nuts, all of which are unprocessed and non-industrial. It’s been well said that one should shop the outer aisles of the grocery store, the inner aisles being where all the processed, industrial junk is sold. The great fitness enthusiast Jack LaLanne once said that if it comes in a box or a bag, don’t eat it. Humans were not meant to do so, and overweight and obesity has been the result.
The food industry has designed fast food to be supremely tasty. It is loaded with salt, fat, and sugar. Fast food should also be avoided too if one wants to lose weight. I doubt that it’s any coincidence that the obesity epidemic has coincided with the increase in fast food outlets. More women have been working outside the home, and more meals are taken in restaurants, and the rates of these have also increased at the same time as obesity has increased. Although there are those who eat this way regularly and don’t gain weight, most people pack on the pounds if they eat fast food.
We were designed by evolution to eat a certain way that would produce robust health, not obesity. But our food environment and hence our choices have changed radically. To get and stay lean, pay attention to what we were meant to eat. Real food does not come from a factory, packaged in shiny bags and boxes. Real food has not been radically altered, but is minimally processed between the time it leaves the farm and the time you eat it.
The admonishment to “just eat real food” can have real benefits. Real food that is minimally processed is unlikely to have addictive properties or to act as supernormal stimuli. Industrial, processed food, especially those foods deliberately designed by the food industry to taste like nothing our senses have tasted before, can cause overeating and, in some people perhaps, a real addiction. Shopping the outer aisles of the supermarket and buying fresh, unprocessed meat, eggs, vegetables, fruit, and so on, will all but ensure that little highly processed food is bought. Skip the bags and boxes of industrial food.
1. Goodman, Elizabeth, and Robert C. Whitaker. “A prospective study of the role of depression in the development and persistence of adolescent obesity.”Pediatrics 110.3 (2002): 497-504.
2. Pan, An, et al. “Bidirectional association between depression and obesity in middle-aged and older women.” International journal of obesity 36.4 (2011): 595-602.
3. Nestler, Eric J. “Molecular basis of long-term plasticity underlying addiction.”Nature Reviews Neuroscience 2.2 (2001): 119-128.
4. Blumenthal, Daniel M., and Mark S. Gold. “Neurobiology of food addiction.”Current Opinion in Clinical Nutrition & Metabolic Care 13.4 (2010): 359-365.
5. Doyle, James Francis, and Farid Pazhoohi. “Natural and augmented breasts: Is what is not natural most attractive?.” Human Ethology Bulletin 27.4 (2012): 4-14.
6. Lenoir, Magalie, et al. “Intense sweetness surpasses cocaine reward.” PloS One 2.8 (2007): e698.