BOSTON—Overweight young adults who have higher insulin secretion may have greater success in losing weight by following a diet with a low glycemic index (GI), rather than a low-fat diet, according to a new study in JAMA (297:2092-2102, 2007). Researchers from Children’s Hospital Boston randomized 73 obese young adults (age 18 to 35 years) for the trial, which included a six-month intensive intervention period and a 12-month follow-up. Serum insulin concentrations at 30 minutes after a 75 g dose of oral glucose was a baseline measure of insulin secretion. The intervention diets were low GI (40 percent carb, 35 percent fat) or low fat (55 percent carb, 20 percent fat).
Changes in body weight and body fat percentage did not differ between the diet groups. However, insulin concentration at 30 minutes after oral glucose did have an effect. Participants with insulin concentration at 30 minutes above the median (57.5 µIU/mL; n = 28) who followed the low-GI diet had a greater decrease in weight (5.8 kg vs. 1.2 kg) and body fat percentage (-2.6 percent vs. -0.9 percent) at 18 months, compared to the low-fat diet. For those individuals with insulin concentration at 30 minutes below the median, there were no differences between diet groups. Additionally, in the full cohort, plasma high-density lipoprotein (HDL) cholesterol and triglyceride concentrations improved more on the low-GI diet, while low-density lipoprotein (LDL) cholesterol concentration improved more on the low-fat diet.
High insulin secretors, therefore, had greater weight loss while following the low GI diet compared to the low fat diet. In addition, the low-GI diet had beneficial effects on HDL cholesterol and triglyceride concentrations.
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