The results regarding amino acid, glucose, insulin, and glycerol concentrations were in line with numerous previous observations.
When it comes to the findings for body composition, this study actually does not prove that whey is superior for maintaining lean mass during weight loss. There’s a fair chance that whey probably is better, but that cannot be determined from these results because this study lacks statistical power to find such differences.
In order for differences between groups to manifest as statistically significant, a sufficient number of subjects must be enrolled. If the between-group difference we are looking at is small relative to the variation in the observations, this calls for more subjects. The study duration was short (14 days) and therefore the changes in lean and fat mass are small compared to the margin of error using a DXA scanner, meaning that if any difference did exist between groups, it would have taken more participants or a longer study duration for significant changes to manifest.
If you know the variation in the measurement you are doing, you can actually calculate the number of subjects needed to detect a group difference of a given size. This is called a power analysis. The researchers actually describe that they knew they had inadequate power to detect between-group differences, which was acceptable as this was not part of the primary objective for the study. Alternatively, this may be a real and valid finding. It is possible that although one protein source may be more effective than another in a short window of time for measuring FPS, overall dietary intake may be most important for producing long-term adaptations in body composition.
What the study did show, however, was that whey stimulates protein synthesis in myofibrillar proteins much more efficiently than soy protein supplementation. How this translates into lean mass sparing during weight loss is very hard to derive for numerous reasons. FPS is normally used as a surrogate biomarker for a snapshot of hypertrophy processes. However, hypertrophy or atrophy is the result of net protein synthesis or degradation, which is again the product of gross protein synthesis and net protein degradation. Therefore, it should be apparent that modulation of protein degradation is just as important as modulation of protein synthesis. This is supported by the results of some studies, which have shown that different protein sources may have different influences on protein synthesis and degradation.
The reason that protein synthesis is more frequently reported is that the technology for measuring protein synthesis is much better than the technology available for measuring protein degradation. All of these factors make it difficult to conclusively state whey’s superiority over soy based on this study. The protein synthesis measurement used in this study is a surrogate for the effect on muscle mass. But changes in muscle mass can be measured directly with something like DXA, albeit this requires a more challenging study setup, meaning more subjects for longer time and a higher study cost. Of course, studies can always be better or more detailed, so maybe this study will be the springboard for the next, more detailed study.
Lastly, funding for this study was provided by the Dairy Research Institute through the Whey Protein Research Consortium. However, the reported findings are in agreement with the literature and with other studies not supported by dairy farmer’s associations.