Battle of the Bulge: The Psychology of Appetite and Diet

Obesity, a growing epidemic in the U.S., is a serious disease many Americans are trying to overcome yet Americans are the ones losing the battle of the bulge. The U.S. Centers for Disease Control and Prevention issued a press release last November indicating that although obesity in adults is statistically insignificant since 2003-2004, an alarming sixty-four percent of America is overweight, and a little over half of that is considered obese. The question: why and how? Studies of eating behavior, in rats and humans alike, have shown that appetite is a complex system that is yet to be understood. Karen Wright, science writer and contributor to Psychology Today, explains in her article, "Consuming Passions," that hunger and craving play an integral part in dieting and weight management. In modern society, where it is common to live to eat as opposed to eat to live, the difference between the two has been obscured. It is easy for one to stop by a fast food restaurant for a meal, especially with dollar menus making the process rather affordable. As a living testament to will power, I know it is a daunting task to lose weight, but I continue to reach my goal. Yes, brain-hunger is a distraction, but a restrictive diet is not suitable to the mind, or the body. A well-balanced diet, regular exercise, and determination can keep that hunger in check.

Hunger, or "stomach-hunger," is the body's way of demanding energy, whereas craving, or "brain-hunger," is the mind's desire to eat for pleasure. An empty stomach produces a hormone called ghrelin, the hormone responsible for those hunger pangs all too common in college students throughout the nation. Ghrelin, in conjunction with a drop in blood-sugar levels and the resulting decline of insulin in the bloodstream, primes the body for a meal. Any food intake produces the hormone leptin, which initiates satiety. These four visceral messengers communicate with the central nervous system to regulate appetite. The hypothalamus, specifically the ventromedial hypothalamus (VMH), is also responsible for regulating appetite; but this antiquated model has been replaced with a biochemical one, one which takes into account neurotransmitters, hormones, peptides, and receptors "within and beyond the hypothalamus," Wright explains. The model, which neuroscientist Satya Kalra of the University of Florida at Gainesville calls the "appetite-regulating orchestra," works like the previous one with notable adaptation: the stomach produces ghrelin, in turn activating the hypothalamus to release the neuropeptide Y (NPY), known as the most potent appetite enhancer thus far. Ghrelin also suppresses the production of proopiomelanocortin (POMC), an appetite inhibitor. Leptin slows the production of neuropeptides Y and promotes POMC production. Some visceral signals reach the brain via nerve cells rather than the bloodstream. A satiety peptide called cholecystokinin (CCK) is released in the small intestine, possibly triggering the vagus nerve, which runs from the stomach to the brain.

Scientists and researchers turned to leptin injections to curb appetite, but to their dismay, it was not the cure to controlling it. In actuality, obese people have high leptin levels leading researchers to think that brain cells of most overweight people do not register leptin for its inhibiting property. Ironically, the body recognizes when there is a deficiency of leptin, which the mind recognizes as an impending loss of body fat, to a dieter's chagrin. The stomach-hunger system has been researched in rats. Psychologist Bartley Hoebel of Princeton University has seen this behavior in his lab rats. By injecting NPY into the brains of rats, Hoebel witnessed feeding frenzies as expected. Unexpectedly, genetically engineered rats with no NPY still ate to satiety. With respect to evolutionary psychology, overeating is an adaptive behavior not needed in modern times. As neurologist Barry E. Levin explains, "Under [conditions of scarcity and unpredictability of food sources], the ability to ingest and store as many calories as possible when food is readily available would have obvious survival value;" thus, humans have become susceptible to easier methods of gaining weight throughout evolution.

In addition, evolution has also provided humans with the added benefit of making eating a pleasurable experience, via neurochemicals and neural circuitry. This is where "brain hunger" comes into play. Food has become not only a means of gustational pleasure--it has also become an addiction and emotional fix. In fact, the same neural signals used in the facilitation of an orgasm are used in brain hunger. Gene-Jack Wang, head of medicine at Brookhaven National Laboratory in Upton, New York states, "Now we're not just talking about energy balance...we're talking human psychology. This stems from brain-imaging studies done on people, where the "mere sight and smell of barbecued chicken, hamburgers, and pizza release dopamine in the striatum." The striatum is a part of the limbic system in the brain that helps create motivation; dopamine is the neurotransmitter responsible for pleasure seeking and produces feeling of enjoyment. The same system is observed in compulsive gamblers and drug addicts, as well as in eating and sex.

Seeing how the same system is implicated in these behaviors, Hoebel proposes that food may have addictive properties. As Wright indicates, high calorie foods cause the release of opioids, a chemical that masks pain and promotes euphoric sensations. Drugs, on the other hand, hijack this network causing the same reaction, only amplified. For dieters, the stomach-hunger/brain-hunger dichotomy is a nightmare. The human mind is not aware of being overweight, but it does detect weight loss--a type of fight or flight response. As losing weight requires eating less calories than physically needed, hunger sets in which drives one to eat. The biochemical model of appetite works against the dieter, where both types of hunger set in. Using strategies, such as substituting unhealthy snacks for healthier ones or drinking a great amount of water before a meal, the individual can satisfy his or her hunger and avoid the repercussions of the mind's need.