The science behind those cookie diets

Some diets just sound like they ought to work: the spinach diet, the grapefruit diet, the cabbage soup diet.

But the cookie diet? Not so much.

It would be sweet if they did, of course. Observes Judith Stern, obesity expert and professor of nutrition at UC Davis: "Wouldn't everybody like to go on a cookie diet?"

While scientific studies of cookie diets are notably lacking, research does offer limited support for some of their claims.

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Proteins

Several promoters of cookie diets say their protein content helps to curb hunger, and two -- Smart for Life and Dr. Siegal's -- chalk this up, at least partly, to the particular amino acids they contain. A number of studies imply that this claim could be true. It has been shown that proteins can help suppress appetite and lead to weight loss, and that in some cases proteins can be more effective than either carbohydrates or fat in reducing the number of calories eaten at the next meal.

The exact mechanics of how proteins have these effects aren't always known. But proteins are formed by chains of amino acids, and some research suggests that certain amino acids may be involved. For instance, a 2006 study in the journal Science found that an amino acid called leucine, which is in meats, grains, nuts and cottage cheese, can have a dramatic effect in reducing appetite and consequent weight gain. Rats that received high doses of leucine ate about 83% as much food over the next day as those who didn't. And if they had fasted for 24 hours, those who received the leucine gained only a third as much weight back the next day as those who hadn't.

The leucine study is far from definitive with respect to cookie diets though. For one thing, it's not even known if leucine is contained in either Smart for Life or Dr. Siegal's cookies, because the companies do not make their amino acid formulas public. Besides, the rats had their leucine injected directly into their brains, near the hypothalamus, the center that regulates hunger and its satisfaction. They didn't just scarf it down in, say, an oatmeal-raisin confection.

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Fiber

With some cookie diets, it's claimed their fiber content helps to curb hunger, and a good deal of research has shown that this is feasible. A 2001 article in the journal Nutrition Reviews summed up the results of studies to date on the effects of fiber on hunger. The authors found that when calorie consumption stays constant, eating more fiber makes people feel more satisfied after a meal and less hungry later. Also, when people can eat as much as they want, they eat 10% fewer calories and lose 4.2 pounds over about four months if they eat an extra 14 grams of fiber per day. And these effects are greater in people who are overweight than those who are not.