Low-Glycemic Diet Is Better Than Low-Fat Diet For Weight Loss

Overweight individuals who over secrete insulin should choose a low-glycemic instead of a low-fat weight loss diet, according to a study reported in the May 16 issue of The Journal of the American Medical Association.

The findings, from a careful study of 73 obese young adults, aged 18-35 years (with a body mass index of 30 kg/m2 and above), demonstrate that hormonal differences — specifically, how much insulin the body makes — help explain whether a diet is successful.

A low-glycemic load diet limits rapidly-digested carbohydrates that sharply raise blood sugar and insulin levels (such as refined wheat and refined sugar) in favor of carbohydrates that raise blood sugar more slowly (such as whole grains, fruits, vegetables, nuts and legumes).

In a study published in The Lancet in 2004, researchers from the Children’s Hospital Boston, in Massachusetts, found that rats whose insulin levels were highest 30 minutes after receiving a dose of oral glucose (sugar) gained the most weight when fed high-glycemic-load diets. They hypothesized that people who make a lot of insulin are similarly sensitive to the effects of glycemic load, and might be more responsive to a low-glycemic load diet.

For this study, participants were randomized to either a low-fat diet or a low-glycemic-load diet. All underwent initial testing to measure their insulin response. The diets involved no calorie restrictions or portion-weighing; instead, dieters received counseling encouraging them to eat until satisfied, changing only the kinds of foods they ate. Every six months, they received unannounced phone calls asking what they ate the day before; based on their responses, the two groups seemed to be adhering similarly to their diets. Protein and fiber consumption, physical activity and satisfaction with the diet were similar for the two groups.

During the first six months, high insulin secretors (those in the top half of insulin secretion) lost 2.2 lbs/month on the low-glycemic-load diet, versus 0.9 lbs/month on the low fat diet. At 18 months, total weight loss was 12.8 lbs in the low-glycemic-load group, but only 2.6 lbs in the low-fat group. Those on the low-glycemic-load diet also had a significantly greater decrease in body-fat percentage, and did not regain weight between six to 18 months — a time when regain virtually always occurs.

Among dieters in the bottom half of insulin secretion, weight loss and changes in body fat did not differ significantly between the low-glycemic-load and low-fat diets.

“These findings can allow clinicians to individualize the treatment of obesity by first giving patients an oral glucose tolerance test,” says David Ludwig, MD, PhD, director of the Optimal Weight for Life clinic at Children’s Hospital Boston and author of the new book Ending the Food Fight: Guide Your Child to a Healthy Weight in a Fast Food/Fake Food World. “People who make a lot of insulin may do especially well on diets that reduce glycemic load. They tend to do very poorly on low-fat diets, which are generally high in carbohydrates and raise insulin levels even further, which in turn causes weight gain.”

Insulin inhibits the activity of a fat-burning hormone called hormone-sensitive lipase, which breaks down the triglyceride in the fat cell allowing free fatty acids to be released into the blood to be used as fuel. When this enzyme is inhibited, the fat is not burned while amino acids from your muscle and carbohydrates are used as fuel instead, which will make you feel hungry when you are not supposed to be.

Source: “Which diet works best may depend on your biology” Children’s Hospital Boston, 15 May 2007; Medscape Today, 16 May 2007 ;JAMA 2007;297:2092-2102

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