First, dieters were flocking to high-protein diets like bees to sugar water. This year, savvy consumers are all abuzz about diets with a low glycemic index (GI). (The GI is a numerical system used to rank foods based on how they affect blood sugar levels; low-GI foods are thought to be heart-friendly and able to curb appetite, promoting weight loss.) Despite the popularity of both high-protein and low-GI diets, until this year no randomized, controlled studies had systematically compared these food plans in terms of their relative effects on weight loss and cardiovascular risk.
Now, a new study has done exactly that. Researchers reporting in the July 24 issue of Archives of Internal Medicine assigned a total of 129 overweight or obese young adults to one of four different weight loss plans for 12 weeks. All were reduced-fat, high-fiber diets. Diets 1 and 2 were high in carbohydrate (55% of total energy intake), with high and low GIs, respectively. Diets 3 and 4 were high in protein (25% of total energy intake), also with high and low GIs, respectively.
Although all the subjects lost weight during the program, the proportion who lost 5% or more of their body weight varied significantly by the type of diet: Of those on diet 1 (high carb/high GI), 31% lost 5% or more, compared with 56% of those on diet 2 (high carb/low GI), 66% on diet 3 (high protein/high GI) and 33% on diet 4 (high protein, low GI). Interestingly, women on diets 2 and 3 lost approximately 80% more body fat mass than those on diet 1. Mean LDL cholesterol levels dropped significantly in the diet 2 group but increased in the diet 3 group.
These results led the researchers to conclude that “both high-protein and low-GI regimens increase body fat loss, but cardiovascular risk reduction is optimized by a high-carbohydrate, low-GI diet.”