In a match-up of whey versus soy, find out which source should be your top pick to decrease bodyfat levels.

By Dwayne N. Jackson, PhD

As a bodybuilder, you know all protein sources aren’t created equal, especially when it comes to putting on lean mass. This thought is generally rooted in research that illustrates differences in their absorption/bioavailability. In the bodybuilding community the use of soy protein is often shunned because of its low bioavailability and potential estrogenic effects, whereas whey protein isolate is held in high regard based on its high bioavailability and anabolic potential.

In recent years, researchers have found that whey protein is more than just a muscle-building supplement. In fact, the latest evidence, published in The Journal of Nutrition, clearly shows that daily whey protein ingestion can significantly decrease fat mass without dieting. This large-scale double-blind, randomized controlled trial was conducted on 90 overweight and obese subjects who were otherwise in good health. They were randomly assigned to one of three groups — whey protein (56 grams/day split into two daily doses), soy protein (56 grams/day split into two daily doses), or maltodextrin (split into two daily doses, containing the same amount of calories as the protein supplements). The subjects were instructed to take their supplement as directed for 23 weeks, given no further dieting advice, and asked to eat as they usually do. Before starting the study period and every month thereafter, participants were weighed, body composition was measured (using BodPod) and waist/hip circumference was recorded. Further, blood and urine were collected before the intervention and at 12, 16, 20 and 23 weeks after supplementation commenced.

At the end of 23 weeks, those who took whey protein had a significant decrease in bodyweight (4 pounds) and fat mass (5 pounds) compared to the maltodextrin group. In contrast, there were no differences in these measures between the soy protein and maltodextrin groups and there were no differences in lean body mass among any of the groups. Furthermore, those who took whey protein had significant reductions in waist circumference compared to the other groups. Interestingly, fasting ghrelin levels (a hormone that makes you feel hungry) were lower in those who took whey protein, suggesting that whey’s weight-loss effects may be (at least partly) a result of decreased hunger.

The Doc's Take

Although this study was conducted on a non-training overweight population, it provides additional support for the use of whey protein among bodybuilders.

First, it’s interesting that subjects lost weight and fat mass without strict dieting and without compromising lean mass. As well, whey protein supplementation decreased ghrelin levels, where soy protein didn’t. Keeping ghrelin levels low is important for bodybuilders, especially those undergoing strict calorie reduction during contest preparation. Based on this study and other related data, it seems daily whey protein supplementation not only helps build lean mass but also aids in regulating bodyfat levels. This area of research is a worthwhile one to keep track of, as further studies may reveal the exact mechanisms behind these effects.

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