VERY 10 years or so, it seems, the country's anxiety over dieting builds to a peak and a realization hits home: Whatever weight-loss program has so recently captivated us is wrong. Fat might be good for us now, some people say, and carbohydrates bad. Not so long ago, the opposite was true. Probably it will be again. These things tend to work the way pendulums do.
Diet fads and government guidelines over the last quarter-century have not helped to produce a slimmer America. We are a fatter country now, on average, than we were in the 1970's. What diet fads have given us are short-term losses and long-term gains because few if any of them emphasize a key fact: If you consume more calories than you expend, you will gain weight. And despite what the opposing sides in this long-running debate assert, it doesn't make much difference where the calories come from. A successful dieter needs to burn them.
At the two poles of the current debate over diet are the protein- and fat-rich Atkins diet and the high-fiber, low-fat program put forward by Dr. Dean Ornish. In the middle sits the Agriculture Department's Food Guide Pyramid, which tells consumers to reduce fats but allows them to increase carbohydrates significantly.
The Atkins diet doesn't seem to restrict calories. In fact, it does. The state of ketosis that all that protein induces makes it difficult for Atkins dieters to consume as many calories as they would by eating refined carbohydrates like sugar, white flour and pasta. Filled with steak, in other words, you're simply too full for dessert or much of anything else.
The Ornish diet is at the other extreme, saying you can eat all you want, but only of foods very low in fat and very high in fiber (complex carbohydrates, in other words: fruits, vegetables and whole grains). The Ornish diet is a low-calorie one for the same reason that Atkins is. Fiber acts like fat. It fills you up.
It all seems very simple: eat fat and protein (Atkins) and a process takes place that most of us don't understand, and you lose weight. Barely eat any fat and stick to complex carbohydrates and the weight will pour off (Ornish).
In both cases it will, at least for the short term. There are no studies to show whether the Atkins diet, in particular, is safe over a lifetime.
Dr. Ornish's diet is designed mainly for people who have clogged arteries or have had heart attacks. Using Dr. Ornish's strict regimen, some of these people have been able to reverse the course of heart disease. Whether the diet is the most desirable for people who are simply overweight has not been determined. There are no lifetime studies.
Caught between these two diet extremes is the Food Guide Pyramid, which tells us that fat should be reduced to 30 percent of calories consumed and that carbohydrates should be increased significantly. It does not, however, distinguish clearly enough between complex carbohydrates (good) and refined ones (bad). Refined carbohydrates turn into blood glucose quickly, which in turn drives up insulin production, which lowers blood sugar and guess what? makes us hungry again. The result is one of unintended consequences.
Since the late 1980's this government-approved diet appears to have provided people with permission to eat as many carbohydrates as they want.
And many of them have.
Over the last 10 or 15 years people have not only continued to consume as much fat as ever, but they have also added 200 to 400 calories a day, much of it from refined carbohydrates. The result is what experts are describing as an epidemic of obesity.
The Agriculture Department is in an untenable position. With the two hats that it wears one to protect consumer health and the other to help farmers sell food it cannot tell us to eat fewer calories. After all, fewer calories generally mean less food, which would fly in the face of the department's mandate to help farmers.
There is another unintended consequence of the government's advice. "The pyramid is designed for the food industry," said Dr. Marion Nestle, chairwoman of the nutrition and food studies department at New York University and author of "Food Politics: How the Food Industry Influences Nutrition and Health."
"They knew exactly what to do with it. They said, 'You want us to sell foods that are low fat or no fat? Sure, but you didn't say anything about calories!' And so the calories remained the same."
Remember Snackwells, the popular cookie of the 1990's? It had no fat but plenty of refined carbohydrates: sweeteners in their various forms. The "no fat" label made many people think it was all right to eat an entire box. In one sitting. No fat, but the cookies still had plenty of calories. They just came from a different source.
At the same time that people increased their consumption of carbohydrates, serving sizes were rising.
Mindy Hermann, a registered dietician in Mount Kisco, N.Y., said: " Everything is supersized. A single serving of a soft drink was once 6 ounces. Today it is 20 ounces. A bagel no longer weighs 2 ounces. It weighs 4 or 6. Hamburgers come in double and triple sizes, with two buns, twice as much cheese and a high-calorie sauce."
Kelly D. Brownell, director of the Yale Center for Eating and Weight Disorders in New Haven, is even more pessimistic. He says it is almost impossible for people to cope with what he calls the nation's "toxic environment."
"The average American child sees 10,000 food ads on television each year," he said. "Bad food and its availability are as much a part of the American environment as clouds and trees."
There are places you never expected to eat, Dr. Brownell said, like gas stations and drugstores and shopping malls. Snack food and soft drink machines are installed in American schools, even as physical education in schools is waning.
"Will power and discipline will take us only so far," Dr. Brownell continued.
At bottom, successful dieters must burn more calories than they consume. Many who beat the odds say that they always feel just a little bit hungry.