Not the same old diet story
At the table, there are a variety of physiologic signals guiding what we now believe to be free will. Two brain chemicals--neuropeptide Y and galanin--control the appetite for carbohydrate-rich and fat-rich foods.
Some revolutions are waged with guns. Others are waged with words. But perhaps the major American revolt of the past two decades has been waged primarily with knife and fork. With butter banished, red meat in retreat, and humble grains advancing on our plates, we've toppled the old dietary regime on the grounds that you are what you eat.
Still, decisive victories in the battle of the bulge, the war on heart disease, and just plain healthy appetites elude us. And so we begin each year with solemn vows to tackle anew our waistlines and our arteries. But if a behavioral scientist in New York is right, a winning strategy can come only from a simple turn of the tables--we eat what we are.
In meticulous studies, Sarah F. Leibowitz, Ph.D., of The Rockefeller University, has discovered that what we put in our mouths and when we do it is profoundly influenced by a brew of neurochemicals based in a specific part of our brain. They not only guide our selection of morsels at breakfast, lunch, and dinner--and even the need for high tea--they are probably the power behind individual differences in appetite and weight gain. They appear to determine whether we are sitting ducks for the eating disorders that now afflict 30 percent of Americans.
Unless we take into account the physiological function of these brain chemicals in dictating natural patterns of food intake and metabolism, we will never get closer than annual avowals in regulating our eating behavior, whatever our reason for doing so. The only plausible way to control body weight is by working with the neurochemical systems that control appetite--and re-tuning them.
Leibowitz's studies point far beyond our forks. They challenge the deeply held belief that we are strictly self-determining individuals acting, at least at the table, by unfettered choice--whim, if the moon is right. Sooner or later, in one context or another, we will have to overhaul our view of human behavior to acknowledge that there are a variety of physiological signals guiding what we now believe to be free will.
Leibowitz, however, has little taste for the philosophical soup. In classic meat-and-potatoes neuroscience, she has located the epicenter of eating behavior. It is a dense cluster of nerve cells, the neurochemicals they produce, and the receptors through which they act and are acted upon. They make up the paraventricular nucleus, deep in the brain's hypothalamus, a structure toward the base of the brain already known to control sexuality and reproduction.
A Matter of Energy
The neurons that affect eating are part of the body's elaborate mechanism for regulating energy balance, the power ensuring that we take in sufficient fuel, in the form of food, to meet internal and external energy demands to survive from day to day. This is perhaps the body's most fundamental need.
Given so crucial a need, the location of the nerve cells of appetite in the hypothalamus is no accident of nature. They are the neurons next door to those that orchestrate sexual behavior. Leibowitz has found that we have clear-cut cycles of preference for high-carbohydrate and fat-rich foods, and they are closely linked to reproductive needs--that is, the ability of humans to survive from generation to generation. After all, the power to reproduce requires that we maintain a sufficient amount of body fat. The group of cells that tangle with sex and the cells that fancy our forks are in constant communication--like the sometimes overprotective mother she is, nature is constantly seeking reassurance that have enough body fat for the survival of the species.
There are, in truth, many other brain areas that influence appetite. But from the lower brain stem up to the thalamus, which controls sensory processes such as taste, and on up to the forebrain and the cortex, where pleasure, affect, and cognitive aspects come into play, everything converges on the hypothalamus. The hypothalamus integrates all of the information affecting appetite. Its neurological signals coordinate our behavior with our physiology.
Through a daunting system of chemical and neural feedback, the brain monitors the energy needs of all body systems moment to moment. And it makes very emphatic suggestions to the stomach as to what we should ingest.
On the menu are the standard nutritional war-horses: carbohydrates for immediate fuel, fat for longer-term energy reserves--it is particularly essential for reproduction--and protein for growth and muscle maintenance. Directives from the brain to the belly are issued by way of neurochemical messengers and hormones. These directives, Leibowitz finds, have their own physiological logic, their own set of rhythms, and are highly nutrient-specific. There's one thing now know for sure--the stomach definitely has a brain.
A Taste for Carbo
In the dietary drama unfolding in Leibowitz's ground-floor laboratory, there are two star players. One is Neuropeptide Y (NPY), a neurochemical that dictates the taste for carbohydrate. Produced by neurons in the paraventricular nucleus (PVN), it literally turns on and off our desire for carbohydrate-rich foods.
Tags:
battle of the bulge,
behavioral scientist,
brain chemicals,
breakfast lunch,
control appetite,
decisive victories,
dietary regime,
galanin,
healthy appetites,
high tea,
knife and fork,
leibowitz,
natural patterns,
neurochemical systems,
physiologic signals,
physiological function,
rockefeller university,
sitting ducks,
solemn vows,
waistlines
