Low glycemic index diet best at reducing weight

A diet rich in carbohydrates with a low glycemic index appears to be more effective in reducing fat mass and lowering the chances of developing cardiovascular disease (CVD) than diets with a high glycemic index or high in protein, an Australian research team reports.

The glycemic index of a food indicates how quickly it is broken down and causes a rise in sugar levels in the blood. Generally, low glycemic index foods are complex carbs like whole grains, rather than refined sugars, for example.

According to a paper in the Archives of Internal Medicine by Dr. Jennie Brand-Miller at the University of Sydney and colleagues, there have been no clinical trials comparing the effects of glycemic index and high-protein diets on weight loss and cardiovascular risk.

They therefore conducted a trial in which 129 overweight subjects ages 18 to 40 were randomly assigned to one of four weight-loss diets for 12-week. All four diets were comprised of reduced fat (30 percent of total energy intake) and held daily calories to to1400 kcal for women and 1900 kcal for men.

The diets varied in target levels of carbohydrates, proteins, and glycemic load (i.e., glycemic index multiplied by the amount of carbohydrate, divided by 100) as follows:

Diet 1: carbohydrates comprise 55 percent of total energy intake, protein 15 percent of total energy intake, high glycemic load (127 g)

Diet 2: similar to diet 1 except a lower glycemic load (75 g)

Diet 3: protein comprises 25 percent total energy intake (based on lean red meat), carbohydrate reduced to 45 percent total energy of intake, and high glycemic load (87 g)

Diet 4: Similar to diet 3, except low glycemic load (54 g).

Brand-Miller and her team report that the diets resulted in similar reductions in weight (4.2 percent to 6.2 percent of body weight), fat mass and waist circumference.

However, in the high-carbohydrate diets, lowering the glycemic load doubled the fat loss.

The investigators also found that total and LDL ("bad") cholesterol levels increased with diet 3 and decreased in diet 2.

"In the short term, our findings suggest that dietary glycemic load, and not just overall energy intake, influences weight loss," the team concludes.

In a related editorial, Dr. Simin Liu, from the University of California in Los Angeles, points out that "foods with a low degree of starch gelatinization, such as pasta, and those containing a high level of viscous soluble fiber, such as whole grain barley, oats, and rye, have slower rates of digestion and lower glycemic index values."

Therefore, the commentator continues, "Without any drastic change in regular dietary habits, one can simply replace high glycemic index grains with low glycemic index grains and starchy vegetables with less starchy ones and cut down on soft drinks that are often poor in nutrients yet high in glycemic load."