Eating More Protein Doesn’t Help You Lean Out? Reanalysis of Often-Cited 36-Week Study Corrects Original Conclusion: Threshold Intakes and Changes (!) in Protein Intake Matter!
I’ve written about both observational and experimental studies that show how increased protein intakes can improve your body composition. So why mention another one?
Well, the study at hand which has been conducted by scientists from the Purdue University is interesting, because (a) it’s not as extreme as Jose Antonios 2014 study in which the subjects consumed “Fivefold More Than the FDA Allows” (learn more), (b) it is not a simple short-term diet intervention where the high protein diet comes – as usual – out victorious and it is (c) actually a re-analysis of one of those studies that is often cited to “prove” that increased protein intakes, let alone the use of whey protein, wouldn’t be advantageous for overweight and obese individuals trying to shed body fat.
But let’s tackle one thing after the other. The original goal of the study at hand was to re-assess the data from Weinheimer’s 2012 study which concluded that “whey protein supplementation [10, 20, 30, or 30 g of whey protein twice daily] does not affect exercise [2x resistance training 1x cardio per week] training-induced changes in body composition and indices of metabolic syndrome in middle-aged overweight and obese adults” (Weinheimer. 2012 | just to make sure you’re not confused: While the lead authors changed Weinheimer <> Campbell, it’s still the same team).
Instead of dealing with absolutes and overall averages, only, Campbell et al. reanalyzed their data to elucidate the influence of total protein intake (TPro) and changes in protein inatke (CTPro) on exercise-induced changes in body composition and metabolic syndrome indexes. As the scientists point out in the introduction to their soon-to-be-published paper, they conducted this assessment from 3 perspectives for protein intake as follows (Campbell. 2015):
- TPro as a continuous variable with the use of a multiple linear regression model;
- CTPro during the intervention vs. each subject s usual protein intake (post-intervention value minus pre-intervention value) with the use of multiple linear regression; and
- TPro as a categorical variable, <1.0, ≥1.0 to <1.2, and ≥1.2 g per kg bodyweight, using a stratified analysis approach.
In that, Campbell et al. (2015) already expected that they would be able to correct their original findings. More specifically, they hypothesized that they’d find that a higher total protein intake, expressed as a continuous or categorical variable, would enhance the training-induced reduction of fat mass (FM) and gain of lean mass (LM), but not influence responses of MetS indexes (these were waist circumference, glucose, TGs, HDL cholesterol, and blood pressure).
Table 1: Overview of the results of the multiple linear regression analysis the beta² are quantitative indicators of the link between total protein intake (TPro) and change in protein intake (CTPro) (Campbell. 2015).
In addition, the scientists were quite convinced that they’d be able to show that the changes in body composition had been the most pronounced in those subjects with the highest increase in total protein intake over the course of the 36 week study period. And guess what!? Campbell et al. were able to confirm both hypotheses in their ahead-of-print paper:
- In conjunction with exercise training, higher total protein intakes promoted positive changes in body composition. What the higher protein intakes did not do, however, was to promote further improvements in critical markers of metabolic syndrome in the 117 overweight and obese middle-aged adults who participated in the 2012 original 36-week intervention.
- In addition, the changes in body composition, Weinheimer et al. observed when they conducted the study three years ago were the most pronounced in those subjects who recorded the largest changes in total protein intake via diet or supplements.
This is why I like the study: You rarely see the same group of scientists go back to their own dataset doing a re-analyses with that far-reaching effects on the original conclusions that were drawn three years ago. Without this kind of thorough research, we’d have even more “irrevocable scientific evidence” pointing us in the wrong direction, only because the analytical methods were not specific enough to give us an idea of the true complexity of the results.
Does this quote sound familiar? It should, it was after all the conclusion of the original study I have seen being cited several times byby various people to argue that increases in protein intake or the use of protein supplements (and specifically whey, which was used in Weinheimer’s original study) would be a waste of time and money.
Figure 1. Temporal changes in the most important markers of body composition according to total protein intake of the subjects during Weinheimer’s 2012 36-week intervention study (Campbell. 2015).
Now that Campbell et al. have published the re-analysis of their own data the correlation coefficients inTable 1 and the data in Figure 1 clearly show that a high and even more so a higher total protein intake can make a highly significant and practically relevant difference when it comes to the long-term effects of exercise on both lean body mass and fat mass. If we take more than just a cursory look we can also make the following statements about the effects of generally high protein intakes and significant increases in protein intake on the basis of the regression coefficients in Table 1:
- For all subjects, higher total protein intakes and higher changes in protein intake were associated with significantly more favorable changes in body composition, fat mass and BMI; only the association with lean mass increases did not reach statistical significance in all subjects.
- The latter is in contrast to increases in protein intake. In subjects who didn’t just have a high baseline protein intake, but who actually ate more protein (from the diet or the whey supplement they received in the original study from 2012), the increase in protein intake was associated with increases in lean mass and decreases in fat mass.
- Comparable results were observed for regional (arms, legs, trunk, android, and gynoid) BM, FM, %FM, LM, and %LM changes (not shown in Table 1).
That’s all great and certainly supports the physique improving benefits of high protein diets. What’s a bit disappointing, though, is that similar correlations between higher or increased total protein intakes were not observed for any of the markers of metabolic syndrome (waist circumference, glucose, TGs, HDL cholesterol, and blood pressure).
So, is eating high(er) protein worth it? Yes, it is. And it’s actually quite important to highlight that sometimes it’s the lack of detailed analyses of the data that may skew the results in ways that conceal health relevant findings. I know, for most doctors “health relevant” improvements would necessarily include the previously mentioned markers of metabolic syndrome, but one thing you must not forget is that those improvements occurred in all subjects in response to the exercise regimen. They were just not statistically significantly augmented in the subjects who consumed the most protein.
Speaking of consuming “the most” protein. If you compare the “high” protein intake in the original study by Weinheimer et al (2012) to the protein intake in the previously cited study by Antonio et al. 1.2g/kg+ is at best a moderate, but by no means a “high” protein intake.
This difference between “really high” (2.5-3.0 g/kg and more) and “RDA-definition high” (more than the RDA of 0.8g/kg) could well be a difference we must not ignore. After all, Campbell’s stratified 2015 analyses of the data showed that the appetite ratings were significantly reduced only in those subjects in the higher, i.e. >1.2g/kg, tertile of protein intakes. If we also take into account whatAntonio et al. (2014) observed in an allegedly different scenario with “really high” protein intakes, we may speculate that even higher protein intakes might (a) have yielded more “spectacular” changes in body composition and (b) have turned non-significant metabolic health advantages in the high protein eaters to significant ones.
References:
- Antonio, Jose, et al. “The effects of consuming a high protein diet (4.4 g/kg/d) on body composition in resistance-trained individuals.” Journal of the International Society of Sports Nutrition 11.1 (2014): 19.
- Campbell, et al. “Higher Total Protein Intake and Change in Total Protein Intake Affect Body Composition but Not Metabolic Syndrome Indexes in Middle-Aged Overweight and Obese Adults Who Performed Resistance and Aerobic Exercise for 36 Weeks.” J. Nutr. jn213595 (2015): Ahead of print.
- Weinheimer, Eileen M., et al. “Whey protein supplementation does not affect exercise training-induced changes in body composition and indices of metabolic syndrome in middle-aged overweight and obese adults.” The Journal of nutrition 142.8 (2012): 1532-1539.