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By Root 1303 0

maintain their proper weight even when allowed to eat as much of it as they wish. But when the same animals are offered a range of tasty snacks, they will inevitably eat more at each meal and increase the number of meals they take. The explanation is an important concept known as sensory-specific satiety. When a human or a rat has filled up on one type of food, and you present him, her, or it with another food that differs in taste, aroma, texture, or even temperature, eating begins all over again. Even though you can’t touch another bite of your main course, you may eat as much of your dessert as if you had not already been dining for the past hour. The modern world is one grand multiethnic cafeteria. The modern world is designed to make you overeat and then ostracize you when you do.

Lurking within your overall appetite are lots of little subappetites, and any one of them can make you overeat. Your urge to begin eating (meal initiation, in the technical jargon) is quite different from your need to keep on eating (meal length), how fast you eat (feeding rate, which usually decreases during a meal), how much you eat overall (meal size, which is the previous two subappetites multiplied together), and how much time will pass before you start eating again (satiety). Distinct chemical signals in the body appear to regulate these different appetites; some of the brain’s sensors shorten a meal’s duration without affecting your feeding rate, and some sensors do just the opposite.

Researchers used to think that chubby people had a special style of eating, taking large mouthfuls in quick succession, each one followed by rapid chewing, but they don’t think so anymore. I eat slowly, take small to medium mouthfuls, chew at a slow-average but extremely steady rate. I rarely let my mouth get empty. But worse, I have a meal termination problem. I simply keep on eating long after everybody else is off powdering her nose or longing for his coffee. Something is amiss with my satiety signals. They don’t tell me when I have had enough.

The biological systems that control each of these subappetites are so complex and convoluted that researchers are only now discovering how they are regulated. Just the sight and smell of food trigger salivation, secretions from your pancreas, and various events in your stomach and intestines. (An obese person’s pancreas turns out four times the insulin when food is sighted or smelled as a skinny person’s pancreas; whether this is a cause or effect of obesity and how it affects appetite are unknown.) Then, as you eat, chemical and mechanical sensors in your mouth, throat, stomach, intestines, and liver send signals to your brain, which not only integrates these reports but can also directly sense glucose in the bloodstream. And both your weight and your body fat are constantly monitored in ways that are not fully understood. It is not surprising that when you fill up on a low-calorie snack made with substitutes for sugar and fat, the brain soon figures out what you’ve done and encourages you to make up for the lost calories somewhere else. Calories, of course, are the most direct and pleasant way to satisfy your appetite, but too many calories are what I am trying to avoid. The only solution is to fool the brain itself.

Several drugs appear to suppress your appetite effectively. These include dexfenfluramine and fluoxetine (the active ingredient in the controversial drug Prozac), both of which increase the availability of serotonin in the brain, which triggers a powerful signal of satiety. In European trials with eight hundred patients taking dexfenfluramine and given psychological counseling, the average subject lost twenty-two pounds in the course of a year; patients who were given counseling alone lost only two-thirds as much. I wish they had tested the drug alone.

Fenfluramine is sold in America under the unappetizing names of Rotondin and Pondimin; the marketing departments must have been on vacation when these drugs were christened. They appear to have more serious side effects, from nausea to impotence,