Purdue University researchers say this is the first meta-analysis to examine what impact whey protein supplementation has on female body composition when factoring in the effects of calorie restriction and resistance training.
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Protein supplementation is touted for increasing muscle mass and strength in men, but one common question when it comes to women is whether protein supplementation will lead to excessive female hypertrophy (“bulkiness.”) Purdue University researchers conducted a meta-analysis addressing this question, now published in Nutrition Reviews.1 According to the researchers, this is the first systematic review and meta-analysis to examine the impact of whey protein supplementation on female body composition when factoring in the effects of calorie restriction and resistance training.
Researchers included data from randomized controlled trials conducted in women who supplemented with whey protein compared to control subjects not supplementing with whey protein. Within each overall group (supplementation and control), researchers classified subjects into the following subgroups: 1) subjects restricting calories via dietary changes, 2) subjects engaged in resistance training, 3) subjects combining calorie restriction and resistance training, and 4) subjects who neither restricted calories nor resistance trained.
The meta-analysis included 488 female participants aged 20-64, and spanned whey protein supplement dosages ranging from 6 g/day to 48 g/day. Whey supplements included those containing whey protein concentrates, isolates, and hydrolysates, but no other protein types (such as casein).
The researchers analyzed changes in whole-body composition, including body mass, lean mass, and fat mass, with or without calorie restriction or resistance training. Overall, researchers found that compared to those not supplementing with whey protein, whey protein subjects overall saw positive, but modest, changes in lean mass and no significant changes in fat mass.
Their subgroup analysis found that among whey protein subjects: 1) the “most robust positive change” in lean mass happened in subjects restricting calories only (but not resistance training), 2) there was no difference in body composition in subjects resistance training only (but not cutting calories), and 3) there was decreased fat mass but no effects on lean or body mass in subjects neither resistance training nor cutting calories. In addition, researchers said there was not enough data to come to a conclusion on the effects in groups both restricting calories and resistance training.
What does this all mean? According to researchers, whey protein caused only modest increases in lean mass, and without influencing fat mass or total body mass, regardless of whether subjects restricted calories or resistance trained. When whey protein supplementation was combined with calorie restriction (such as during a weight-loss program), the increases in lean body mass were more pronounced.
Again, any increase in lean mass was moderate only, leading the researchers to conclude that “[t]his moderate increase in lean mass over time (0.37 kg) represents <1% of the total lean mass of study participants and therefore does not support the public perception that [whey protein] causes excessive hypertrophy or ‘bulkiness’ in adult women.”
The researchers wrote: “In summary, findings from this systematic review and meta-analysis indicate that [whey protein] supplementation improves body composition in adult women by modestly increasing lean mass without influencing changes in fat mass.”
In addition, they added, “Whey protein may be more beneficial for improving body composition when included as part of a weight-loss program. Although more research is needed to specifically assess the effects in varying states of energy sufficiency and exercise training, the overall findings support consumption of [whey protein] in women seeking to modestly improve body composition.”
This study was funded by the U.S. Whey Protein Research Consortium, an industry-funded research and education group whose partners include dairy cooperatives, dairy associations, dairy processors, and multinational companies.
The researchers noted that “females are underrepresented in this line of research,” with most studies examining whey protein’s effects performed in male-only populations. In general, they pointed out, “there is a paucity of protein supplementation research in women.”