Low-glycemic diets under study for weight loss

A low-glycemic-load diet enhanced weight loss among certain volunteers on a reduced-calorie diet for six months. The significant level of weight loss was limited to those among the study participants who where considered “high-insulin-secreting.” The findings could lead to more customized weight-loss strategies in the future, though the results must be replicated in a larger study before being considered definitive.

The study findings were published in the December 2005 issue of Diabetes Care.

Senior authors Susan Roberts and Andrew Greenberg were funded by the Agricultural Research Service (ARS). Roberts is director of the Energy Metabolism Laboratory, and Greenberg is director of the Obesity and Metabolism Laboratory, both at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University (HNRCA). Lead author Anastassios G. Pittas is with the Tufts-New England Medical Center. Both centers are based in Boston, Mass.

Roberts, Greenberg and Pittas worked with coauthors at both centers. The study was performed at the HNRCA as part of a trial funded by the National Institutes of Health.

The volunteers were all healthy but overweight adults–aged 24 to 42 years. Each was given a diet that provided 30 percent fewer calories than his or her baseline calorie needs. Half the participants were randomly assigned to a low-glycemic-load diet of 40 percent carbohydrates, 30 percent protein and 30 percent fat. The other half consumed a high-glycemic-load diet: 60 percent carbohydrates, 20 percent protein and 20 percent fat.

All participants lost some weight as a result of restricting calories, but those who lost the most had high baseline levels of insulin secretion and ate the low-glycemic-load diet.

Glycemic load is a relative measure of how much carbohydrate is in the diet combined with how quickly that food is converted in the body to blood sugar. The volunteers’ insulin secretion levels were based on their responses to a standard, two-hour oral glucose tolerance test.

Further studies are planned for larger groups of volunteers.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.

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