Researchers at the U.S. Department of Agriculture's Human Nutrition Research Center randomly assigned 90 overweight and obese middle-aged adults to one of three groups. The first group was asked to add protein drinks made with whey to their normal diets, the second group drank protein drinks made with soy protein, and the third group drank carbohydrate drinks.
Study participants weren't told which group they had been assigned to. All the drinks, which were drunk twice daily, at breakfast and dinner, had the same number of calories: 200. They also all had had 52 grams per packet, for a daily total of 104 grams of added protein or carbs.
Researchers tracked participants' physical activity levels, weights, waist sizes, lean and fat body mass, and blood levels of hormones related to hunger and metabolism.
They also had people keep records of the other foods they were eating. The researchers made sure participants were drinking the shakes during random urine tests for levels of a chemical tracer they had added to the powders.
Whey Protein vs. Soy Protein
When the study started, there were no significant differences between groups, researchers report.
Men weighed an average of 218 pounds, while women weighed an average of about 190 pounds.
Throughout the study, all the groups ate roughly the same number of average daily calories, about 2,200.
After six months, people drinking the carbohydrate shakes had gained a little bit of weight, about 2 pounds, which appeared to be mainly added fat, compared to where they started.
People drinking the soy shakes had stayed about the same weight as where they started.
But people drinking the whey protein had lost a little bit of weight and body fat, about 2 pounds. Additionally, while the other groups saw little change in the size of their waists, the whey protein group lost about an inch around the middle.
Reference: http://tinyurl.com/jxe2736
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