Thursday, May 17, 2007

Effect of a weight-loss diet may depend on individual insulin secretion

A study comparing two weight-loss diets found that a one providing a low glycaemic load gave better outcomes than a low fat diet in individuals with high insulin secretion. The authors of the study note that clinical trials of weight loss diets have given inconsistent results and suggest that this may be because inherent physiological differences in participants could modify their response to particular regimens. They suggest that insulin secretion could be such a modifying factors, and therefore studied the effects of two different diets in a group of individuals whose insulin response to a glucose load had been measured. Their hypothesis was that those with a high insulin secretion may be most sensitive to a glycaemic load. The study diets were designed as low glycaemic load / higher fat (40% carbohydrate and 35% fat), and low fat / higher glycaemic load (55% carbohydrate and 20% fat). Participants were overweight or obese young adults who were randomised to one or other diet after having a standard oral glucose tolerance test. They had a six-month intensive intervention period followed by a twelve-month follow-up, and were assessed at 6, 12, and 18 months. Primary outcomes were body weight, body fat percentage, and cardiovascular risk factor levels.

A total of 227 individuals were assessed for eligibility, of whom 73 were randomised (15 male, 58 female); 52 completed the 18 month follow-up. Baseline measurements were broadly similar for the two groups. Overall changes in body weight and body fat percentage were similar for both diets, with mean loss in weight of around 2 to 3kg at 18 months and 1 to 1.5 reduction in body fat percentage. The effect was modified by insulin secretion level, however: those with high levels had greater weight loss ((–5.8 vs –1.2 kg; P = .004) and loss of body fat (–2.6% vs –0.9%; P = .03) with the low glycaemic load diet compared to the low-fat diet. Across the whole cohort, the low glycaemic load diet improved levels of triglycerides and HDL cholesterol, and the low fat diet improved levels of LDL cholesterol.

The authors conclude that variability in the results from weight loss trials may be due to the influence of hormonal factors. In individuals with a high insulin response to a glucose load, a low glycaemic load diet may be particularly valuable. In all dieters, low glycaemic load diets are likely to improve HDL cholesterol and triglyceride levels, whereas low fat diets will improve LDL cholesterol levels.

JAMA 2007; 297; 2092-102 (link to abstract)

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