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.
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.
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.
Still, none of these studies prove anything about cookie diets. There is no official recommended daily amount for fiber, but a number of health organizations recommend from 20 to 35 grams a day. The amount of fiber a person gets per day from cookie-diet cookies ranges from 6 grams a day to 12. Of course, cookie dieters should be eating fewer calories a day than most people, and they should be getting additional fiber in the one or two other meals they eat.
Broad support also exists for the notion that small frequent meals can stifle hunger pangs more effectively than the standard big three. For example, two studies in 1999, one with obese men and one with nonobese men, found that such downsized dining took a large bite out of appetites. In both studies, the men were fed the same amount of food either in one big breakfast or divided into five small ones eaten at hourly intervals. Afterward, for lunch, they could have however much food they wanted. In both cases, the men who ate the big breakfast consumed 27% more calories than the men who ate the five small meals. Surprisingly, this difference was not reflected in hunger ratings.
When men ate the single big breakfast, their blood insulin levels spiked and then fell. Insulin levels rose for frequent eaters too, but not nearly so sharply, and they never dropped as low either.
One purpose insulin serves is to "open" cells and let in blood sugar to provide fuel. This lowers blood sugar levels, and that makes you hungry. But in the brain, insulin actually acts to curb appetite. Ideally, this would make you eat just the right amount, but it's easy for the balance to get out of kilter -- in the direction of eating too much. Many nutrition experts believe that the spiking and falling of insulin levels contribute to things running amok and that a steadier state of insulin levels keeps things in line.