A meta-analysis that included 14 randomized controlled trials with a total of 626 adult participants found that  whey protein, either as a supplement combined with resistance exercise or as part of a weight-loss or weight-maintenance diet, may provide men and women benefits related to body composition.

Included weight loss studies that used whey protein to replace calories in the diet showed participants had a decrease in body weight of 4.2 kg (9.2 pounds), on average, compared to baseline values with whey protein intake. Additionally, after analyzing muscle protein synthesis studies that included resistance exercise along with whey provisions, researchers found that participants had a statistically significant increase in lean body mass of 2.24 kg (4.9 pounds,) on average, when whey protein was used in conjunction with resistance exercise.  

Whey protein is a high-quality protein naturally found in dairy. It is a complete protein containing all of the essential amino acids ("building blocks") the body needs, and is rapidly digestible. Whey protein is also one of the best sources of a subgroup of three essential amino acids, called branched-chain amino acids (BCAAs), which include leucine, isoleucine and valine. Unlike other amino acids, BCAAs are almost exclusively taken up and used by muscle. And, among common food sources of BCAAs, whey protein contains one of the highest levels of leucine, which has been shown to influence muscle growth.

"There is a growing body of research that supports the benefits of whey protein for weight maintenance and lean body mass," said Dominik D. Alexander, PhD, MSPH , principal investigator. "By conducting this meta-analysis we were able to better evaluate the collective power of each individual study. The results indicate that there is something unique about whey protein, compared to other protein sources and carbohydrates, when it comes to building lean body mass and maintaining or losing weight."

Study Details

The Study: A meta-analysis was conducted to examine the effect of whey protein (WP),with or without resistance exercise, on body weight and body composition in randomized controlled trials (RCTs) conducted in generally healthy adult study populations.

A comprehensive literature search was conducted to identify RCTs that investigated WP (concentrate, isolate, or hydrolystate) and body weight, body mass index (BMI), body fat,lean body mass (LBM), fat-free mass (FFM), and waist circumference. Random effects meta-analyses were conducted to generate weighted group mean differences (WGMD) for between group comparisons (WP vs. other protein sources or carbohydrates) and within-WP group comparisons (i.e., differences from baseline to trial end).

Studies were classified into two distinct groups—WP as a supplement without dietary modification (WPS) and WP as a replacement for other sources of calories (WPR)—and were meta-analyzed separately. Subgroup analyses included examining the effect of resistance exercise and type of WP on the relationship between WP and body composition.

Results: Fourteen RCTs were included, with a total of 626 adult study completers. Five studies examined the effects of WPR whereas the remaining nine studies examined the effects of WPS. Body weight (WGMD: -4.20kg, 95% CI: -7.67, -0.73) and body fat (WGMD: -3.74kg, 95% CI: -19 5.98, -1.50) were significantly decreased from baseline in the WPR within-group analyses.

In the between-group analyses, the effects of WP were more favorable when compared with carbohydrates than protein sources other than whey, although findings did not reach statistical significance. Results from the subgroup analyses indicated a statistically significant increase in LBM (WGMD: 2.24 kg, 95% CI: 0.66, 3.81) among studies that included a resistance exercise component along with whey protein provision.

Another study by Dr. David Baer, USDA, found that daily consumption of whey protein, but not soy protein, led to lower body weight, body fat and waist circumference compared to carbohydrates in free-living overweight and obese adults.