When It Comes to Dieting, It May Not Be All About the Calories
In the battle of the diet plans, the main question is: Which one works best? Perhaps, though, the real question should be: Whom is it best for? A study published today in the Journal of the American Medical Association finds that you may do better on a lower-carbohydrate diet if you naturally release high levels of the hormone insulin after eating sweets and starches. "It's so commonly stated that weight loss is determined by calories in and calories out," says study coauthor David Ludwig, director of the optimal weight for life program at Children's Hospital in Boston. Though calories still count, he says, they may not tell the whole story.
In the study, 73 obese adults had a base-line blood test to measure their spike in insulin levels 30 minutes after consuming a sugary drink and were then randomly divided into two groups. (Diabetics who have chronically high insulin levels were not included in the study.) The first group was taught to eat meals with 40 percent of calories coming from "low glycemic load" carbohydrates (fruits, vegetables, unprocessed whole grains) that slow the release of insulin, 35 percent of calories from fat, and the rest from protein. The second group was told to make meals with 55 percent of their calories from any carbs (including bread, rice, and pasta) but with just 20 percent of calories coming from fat. Both groups were also told to limit sweets and junk food and to write down everything they ate. After six months, those who had the highest insulin spikes at the beginning of the study were down nearly 13 pounds on the low-carbohydrate diet compared with an average weight loss of 5 pounds for high insulin secretors on the low-fat diet and low insulin secretors on both diets. (Food diaries showed that all groups had cut their calories by about 400 a day on average.) Eighteen months into the study, the high insulin group on the low-carb diet maintained their weight loss while the others showed a regain of 3 of the 5 lost pounds.
While small, and discounting for the possibility that participants didn't accurately record their food intake, the study adds to evidence from two other studieswhich previously found that low-glycemic load diets work better in those who are high insulin secretors. One of the studies also found that low insulin secretors lose more weight on higher carbohydrate diets, though that wasn't seen in this new study. Insulin drives sugar into cells for storage, so those who produce excess amounts after eating too many carbohydrates may have more of a tendency to put on fat. By the same token, when insulin levels plunge by cutting down on carbs, these folks may have an easier time shedding weight. "These findings are very exciting because they help explain why some lose a tremendous amount of weight on a particular diet while others don't," says Anastassios G. Pittas, an assistant professor of medicine at Tufts-New England Medical Center who led one of the previous studies.
The bottom line: Before you pick a diet, first determine if you're a "high insulin secretor" by asking your doctor to perform a routine glucose tolerance blood test that involves drinking a sugar solution and having a blood sample drawn 30 minutes later. Though a normal range hasn't been established, high secretors in the study had insulin levels above 57.5 µIU/mL. It may be easier, though, just to tinker with your eating plan to see what works best. "This kind of study tells you that if you're on a diet and having trouble with it, why not experiment?" says Marion Nestle, a professor of nutrition at New York University and author of What to Eat. "Without even having your insulin measured, you can try going on a lower carbohydrate diet and seeing if it helps."