Low GI diet may help keep weight off
metabolism than low-fat diets, making dieters feel less tired, cold
and hungry and more likely to stick to the regime long-term,
suggests a new study.
The study also found that the low glycaemic diet improved cardiovascular risk factors to a greater extent than the low-fat diet.
Reduction in glycaemic load may therefore aid in the prevention or treatment of obesity, cardiovascular disease, and type 2 diabetes, said the researchers from Harvard University.
For example, insulin resistance decreased by more than twice as much with weight loss in the low-glycaemic load versus the low-fat group, reported the researchers in the 24 November issue of the Journal of the American Medical Association (292, pp2482-2490).
The findings offer further support for the glycaemic index, a method of measuring foods based on their effect on blood sugar levels, that is seeing increasing interest in western populations looking to reduce the risk of obesity-related disease.
The low-glycemic-load diet reduces carbohydrates that are rapidly digested and that raise blood sugar and insulin to high levels - such as white bread, refined breakfast cereals, and concentrated sugars. Instead, it emphasizes carbohydrates that release sugar more slowly, including wholegrains, most fruits, vegetables, nuts, and legumes.
It is generally agreed that further research is needed to demonstrate the benefits of this approach, originally designed for diabetics, for healthy people looking to reduce risk of heart disease and control their weight.
But the new study reveals some potential advantages over a conventional low-fat diet.
For example, it suggests that those on a low-glycemic load diet would be more likely to keep weight off than those on a low fat diet. In the trial, resting energy expenditure (REE) of GI dieters decreased less than with the low-fat diet, which could amount to several pounds of weight change per year, given this effect would persist over a long term, said the researchers.
"Composition of diet may impact how dieters respond to weight loss," noted lead researcher, Mark Pereira, now assistant professor in epidemiology at the University of Minnesota.
"On a typical low-fat diet, the participants tended to experience more perceived hunger and a slower metabolic rate, which may make it more difficult to stay on the diet, while those on the low-glycaemic load diet did not feel as hungry and had a faster metabolic rate."
Pereira and colleagues at Harvard University designed a randomized parallel-design study of 39 overweight or obese young adults aged 21 to 40 years who received an energy-restricted diet - either low-glycaemic load or low-fat. Participants' body composition, REE, blood cholesterol, blood pressure and blood glucose and insulin levels were measured and studied before and after 10 per cent weight loss.
"Our data suggest that the type of calories consumed - independent of the amount - can alter metabolic rate," said Dr David Ludwig, the study's senior investigator. "That hasn't been shown before. The idea that 'a calorie is a calorie is a calorie' doesn't really explain why conventional weight-loss diets usually don't work for more than a few months."
Children's Hospital Boston is currently recruiting adults for a large-scale, 18-month study of the low-GL diet.
