A new US study on obese young adults showed that the ones who secreted a high level of insulin shed more pounds on a low glycemic diet than on a low fat diet. The results also suggest that a low glycemic diet is more beneficial to HDL (good) cholesterol and triglyceride levels in this group. The study is published in the Journal of the American Medical Association (JAMA). Obesity is becoming a major medical problem, affecting one third of the US population. Finding diets that work is not easy. Three popular diets, low glycemic, low carbohydrate and low fat have been receiving much attention recently, but, according to Dr Cara Ebbeling, of the Children's Hospital in Boston, Massachusetts, and colleagues, who performed the study: "Clinical trials have produced inconsistent findings, with some suggesting that one diet is superior for weight loss and others indicating no difference between diets." The researchers wondered if the inconsistent findings could be explained by inherent physiological differences among the participants: "One physiological mechanism that might relate weight loss to dietary composition is individual differences in insulin secretion," they wrote. Dr Ebbeling and colleagues conducted a randomized controlled trial to find out the extent to which two different diets (low glycemic and low fat) affected loss of body weight and body fat in obese people with varying patterns of insulin secretion. They recruited 73 young adults aged from 18 to 35 years to take part in the trial which ran from September 2004 to December 2006. The first 6 months was an intensive intervention period where they followed a diet, and then they were followed for another 12 months. Each participant was randomly assigned to follow either a low glycemic diet (40 percent carbohydrate and 35 percent fat) or a low fat diet (55 percent carbohydrate and 20 percent fat). Their blood insulin was measured at the start of the trial, then at 6, 12 and 18 months. This was done by testing their blood 30 minutes after they had ingested a sugary drink containing 75 g of glucose. (The 30 minute insulin level). The results showed that: Overall, the change in body weight and body fat did not differ between the diet groups. However, those participants with a 30 minute insulin level above the mid point (median) achieved more weight and body fat loss on a low glycemic diet than on a low fat diet. At 18 months, their weight loss was 12.8 lb (5.8 kg) on the low glycemic diet versus 2.6 lb (1.2 kg) on the low fat diet, and their corresponding body fat loss was 2.6 per cent versus 0.9 per cent respectively. For all participants, regardless of insulin patterns, the level of high density lipoprotein (HDL, or "good" cholesterol) and triglyceride concentrations improved more on the low glycemic diet, whereas the low density lipoprotein (LDL or "bad" cholesterol) improved more on the low fat diet. For those participants with 30 minute insulin levels below the mid point, there was no significant differences in weight and body fat loss between the two diets. Cardiovascular risk factors did not differ between high and low insulin secreters. The authors concluded that: "The main finding of our study is that a simple measure of insulin secretion predicted weight and body fat loss on low-glycemic load and low-fat diets." "For obese individuals with high insulin concentration at 30 minutes during an oral glucose tolerance test, a low-glycemic load diet may promote more weight and body fat loss than a low-fat diet. Regardless of insulin secretion, a low-glycemic load diet has beneficial effects on concentrations of HDL cholesterol and triglycerides but not on LDL cholesterol," they added. However, they cautioned that because this study was on obese young adults, the findings may not apply to the population at large. They called for more research into how individual physiology, such as insulin levels, affects the results of different diets. "Effects of a Low-Glycemic Load vs Low-Fat Diet in Obese Young Adults: A Randomized Trial." Cara B. Ebbeling, Michael M. Leidig, Henry A. Feldman, Margaret M. Lovesky, David S. Ludwig. JAMA. 2007;297:2092-2102. Vol. 297 No. 19, May 16, 2007.