Winning at Losing
Your body's use of insulin may point to the right diet
As diet books battle one another to the top of the bestseller lists, diet researchers now say we should rethink the one-size-fits-all approach to weight loss. A study published in last week's Journal of the American Medical Association found that certain people, who get a hefty surge of the hormone insulin every time they eat a bagel or double-fudge brownie, shed more weight on diets that contain fewer carbohydrates and more fat. Those who pump out less insulin don't reap the same benefits. "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.
Weight-loss researchers have long known that participants in diet studies who are fed identical meals often lose vastly different amounts of weight and that part of the reason may be differences in their bodies such as metabolism or hormones. They've recently focused the spotlight on insulin, which drives sugar into cells for storage and causes weight gain in carb lovers who produce too much of the hormone.
10-pound gap. In the JAMA study, researchers measured the insulin levels of 73 obese adults, without diabetes, after they drank a sugary beverage. One group was told to reduce carbohydrate intake to no more than 40 percent of calories and to consume unrefined or "low glycemic load" carbohydrates like fruits, vegetables, and barley to keep their insulin levels down. A second group could eat a variety of carbs but had to restrict fat intake to 20 percent of calories. After 18 months, participants who had the highest insulin spikes at the beginning of the study had lost nearly 13 pounds on the low-glycemic-load diet; their counterparts on a low-fat diet shed an average of just 3 pounds. The low insulin makers in the study lost the same 3 pounds regardless of which diet they followed. Yet all of the groups had cut their intake by about 400 calories a day.
What explains the different diet outcomes? "Most high insulin secretors have probably been following a low-fat, high-carb diet for years, so they packed on extra weight that easily comes off once they lower their insulin levels," explains Ludwig. Those who make less insulin could take a more flexible diet approach, but they might need to slash calories by greater amounts. Other research suggests that a low-fat diet may even be preferable, but that needs to be further studied, says Anastassios Pittas, an assistant professor of medicine at Tufts-New England Medical Center. Ideally, people should work with a doctor or nutritionist to tailor a dietary plan that's likely to be effective for them, says Marion Nestle, a professor of nutrition at New York University and author of What to Eat.
It may not be a bad idea to find out if you're a "high insulin secretor." A routine glucose tolerance blood test that involves drinking a sugar solution and having a blood sample drawn 30 minutes later will yield the answer. Though a normal range has not been established, high secretors in the JAMA study had insulin levels above 57.5 micro international units per milliliter. 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 Nestle. "Without even having your insulin measured, you can try going on a lower-carbohydrate diet and seeing if it helps."
This story appears in the May 28, 2007 print edition of U.S. News & World Report.