These ground-breaking studies of nutrient preferences show that inborn patterns are one way we can be set up for eating problems or weight gain we might prefer not to have. They also implicate another--stress. Stress potentially wreaks havoc with our eating patterns by altering us internally.
When we feel under stress, the body increases production of the hormone cortisol, from the adrenal gland. The purpose of this chemical messenger of alarm is to marshall forces of energy for immediate use--to prepare us, as it were, for fight or flight. it puts our whole system on alert, and makes us hyper-vigilant.
As it enters the bloodstream from the adrenal gland and circulates throughout the body, cortisol sees that carbohydrate, stored in muscles and liver as glycogen, is swiftly turned into glucose for fuel. If we are not burning up glucose, we have no energy. One reason cortisol is elevated in the morning is because the food deprivation of overnight fasting is a kind of stress to the body, destabilizing the system.
Cortisol, however, is also critical in the regulation of the neurochemicals that control eating behavior. "It up-regulates the neuropeptides when you don't want it to," says Leibowitz. Cortisol specifically stimulates production of Neuropeptide Y, which turns on the appetite--for more carbohydrate. "Stress is very much related to turning on Neuropeptide Y," reports Leibowitz. "It doesn't appear to increase galanin."
What's particularly tricky is that the effect of stress on eating is not uniform throughout the day. A bout of stress at the right time in the morning may keep Neuropeptide Y turned on all day. "We know that some people under stress get fat and others do not overeat. It depends on when the stress is occurring. Wouldn't it be nice to get your stress at a time when you are not so vulnerable?" Now if only she knew when that was.
Why We Overeat
What she does know is that if there is no muscular activity to use up the carbohydrate stress sets us up to eat, the carbohydrate is put directly into storage as fat. But wait--there are other consequences. It is an axiom of neuroscience that the same chemical messenger has different effects at different sites.
Through neurochemical cross talk in the hypothalamus, the increase in Neuropeptide Y activity affects the master switch for sexual and reproductive behavior in the cluster of cells next door. In this back-and-forth signaling between cell groups, high levels of Neuropeptide Y, hellbent on carbohydrate intake, turn off the gonadal hormones, which are far more interested in fat. The upshot is a dampening of sexual interest and activity. This effect turns out to be critically important in anorexia.
Eating carbohydrate under stress, however, has something going for it. It chases away the stress-induced changes in neurochemistry. The hormonal alarm signals dissipate. "After we eat a carbohydrate-rich meal, the world actually seems better," explains Leibowitz. We feel less edgy. "That's why we overeat."
Dieting--Bad for the Brain
Many studies have shown that curbing body weight by food restriction--dieting--makes no sense metabolically; in fact it's counterproductive. Leibowitz finds it also makes no sense to the biochemistry of our brains, either. "All dieting does is disturb the system," she says emphatically. "It puts you in a psychologically altered state. You're a different person. You respond differently."
Erratically skipping meals upsets the natural daily rhythm of neurochemicals; "that's important because the body works on routines. If you disturb the routine, you're going to be a different person at lunch than if you didn't skip breakfast." What's more, "the chemicals that regulate appetite also directly affect moods and state of mind, our physical energy, the quality of our sex lives," says Leibowitz.
Fasting--restricting, in the parlance of those who study eating behavior--is particularly counterproductive to appetite. It simply turns on the neurochemical switches. "It's got to come out somehow," says Leibowitz. It specifically drives up levels of Neuropeptide Y and cortisol. Then, when the next meal rolls around, it turns it into a high-carbohydrate binge. "Neuropeptide Y is truly the neurochemical of food deprivation." Fasting or dieting drives the body to seek more carbohydrate. Her studies show that animals that love carbohydrate have higher levels of Neuropeptide Y in the paraventricular nucleus.
The Way We Were
How, then, to lose weight? Certainly not diet pills. One reason they don't work is that they don't even aspire to cope with the array of neurochemicals setting the table for appetite. Assuming such an approach to be possible or even desirable, it would, in fact, take assorted concoctions of chemicals at different times of the day, since each meal is regulated differently.
Nevertheless, the way to control appetite and body weight, Leibowitz believes, is by working with the neurochemical systems--and re-tuning them. "We need to help people understand what they are and what their appetite is, and how to work with the body the way it is. Some people are more sensitive." This may be a far gentler approach than skipping lunch, but in the long run, it may be the only workable one, the only one that can possibly do away with the preoccupation with dieting that now consumes 50 to 70 percent of all women.
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