More Protein = Less Fat: Additional(!) Whey, But Not Soy, Induces Slight Body Fat Decrease in Obese Individuals Without Conscious Dietary Intervention(s)

Image 1: Whey proteins are cheap,
many are tasty and as this study
shows, effective not only for increases
in lean, but also for reductions in fat mass.
As a faithful visitor of the SuppVersity, it won't surprise you to read about the counter-intuitive effects the addition of 56g of whey protein to the diet of ninety overweight and obese patients (BMI ~30kg/m²; age 51y) had in a study the results of which have finally been published in the Journal of Nutrition on June 15 (Baer. 2011). What could be news to you, however, is that the same amount of soy protein failed to induce similar changes.

David J. Baer and his colleagues from the Human Nutrition Research Center in Beltsville (note: this institute is financed by the USDA) instructed the participants of the study to add 56g of a supplement containing either whey (WP), soy protein (SP) or carbohydrate (CHO) to their regular diets for 23 weeks - other than that participants were not provided any dietary advice and were supposed to continue to consume their free-choice diets.

The supplements were supposed to be taken in divided doses with breakfast and dinner, respectively. Most subjects chose to consume their protein either before of with those meals (breakfast: 80%; dinner: 72%). Yet other than one would have suspected...
[t]he dietary treatments did not affect hunger (P = 0.11), desire to eat (P = 0.11), prospective consumption (P = 0.38), or stomach fullness (P = 0.62).
Unfortunately, the study is lacking objective information about the effective macronutrient intake of the individuals. Based on the very subjective visual analogue scale (VAS) questionnaire that was used to 'measure' satiety it is however impossible to exclude the possibility that the subjects just (over-)compensated for the additional 417kcal they consumed in form of supplements. This holds especially true in view of the fact that over a time course of 23 weeks, even a minimal reduction of 42.5-52.5 kcal/day should (assuming the flawed calories in vs. calories out hypothesis were true) have facilitated the exact same weight reductions.

The lack of information about the overall caloric value and macronutrient composition of the subjects' diets is thus a very unfortunate shortcoming of the study, you should keep in mind, when looking at the changes in body composition, which as a closer look at the data in figure 1 shows were marginal [0.1% fat mass lost per week is not really impressive, is it?], anyway.
Figure 1: Changes in body composition and waist circumference relative to baseline in obese individuals supplemented with carbohydrate, whey or soy protein beverage over the course of 23 weeks (data calculated on the basis of Baer. 2011)
Despite the fact that the abolute effect of this 'dietary intervention' was relatively small, the relative changes in body composition and morphology, I calculated and plotted in figure 1, make it quite obvious that only individuals consuming the whey protein shakes saw beneficial effects on both their body fat, as well as the circumference of their waistline. On the other hand, the addition of soy protein produced the largest increases in IGF-1 (cf. figure 2), yet without any statistically significant effect on body composition or morphology. The carbohydrate group, lastly, experienced a significant, yet completely undesirable recompositioning effect with an overall increase in body fat of >3.5%. In view of the negligible increase in waist circumference, it is worth to note that their bodies obviously distributed evenly across all fat depots.
Figure 2: Serum markers of the three groups after 23 weeks of supplemental carbohydrate, whey or soy protein (data adapted from Baer. 2011)
With the differences between blood parameters other than IGF-1 and ghrelin being non-significant [especially the metabolically relevant thyroid hormones T3 & T4], it is difficult to find any reasons other than compensatory effects due to (unconscious, but well existent) increases in satiety. This holds especially true, in view of the fact that "[b]ased on the length of the treatment and the daily energy provided from the supplement", the scientists had estimated that "weight gain would exceed ~10 kg without any compensation for the additional energy of the supplement." If we now have a look at the hunger-hormone ghrelin (cf. figure 2), its elevation, or reduction (vs. soy protein as a median that left the weight of the participants unchanged) in the carbohydrate and whey group, respectively, this would corroborate my initial hypothesis that the 90 men and women participating in this study may, without even noticing it, have reduced their total caloric intake by exactly those 42.5-52.5 kcal/day that, in conjunction with an overall improvement in the macronutrient composition of their meals (meaning a higher protein content), allowed them to drop those 2.3kg of fat in the course of those 23 weeks on whey protein supplements.

Edit: My buddy Sean from CasePerformance reminded me of a study by Hartman et al. (Hartman. 2007) from the McMaster University Medical Center in Hamilton, ON, Canada from 2007. Despite being published in the "Pre-SuppVersity Ages" some of you may remember this study, as it triggered a series of reports that brought milk back to the radar as a potent post-workout supplement. The study showed that compared to a soy formula a milk-derived post-workout shake (17.5 g protein, 25.7 g carbohydrate, 0.4 g fat) facilitated greater increases in type II muscle size and lean mass while reducing fat gain at roughly equal overall body weight gains. Sean also points out that - other than in the study at hand - Hartman et al. also recorded total caloric intake and found no statistical significant differences between the two groups, whether or not this allows for any inferences on the actual caloric intake of the obese subjects in the Baer study is questionable, however. After all, you ought to be hungry after a workout and you probably know that no matter how large your post-workout drink may be, you're going to be hungry again about 1h after...
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