Today’s post will be short and sweet.
Previously I covered the topic of excess protein being converted to fatty acids and contributing to fat gain (found here, here and here; this was a rather popular one). In those articles, I concluded by saying that while the metabolic pathways to convert amino acids to fatty acids do indeed exist in humans, the fact of the matter is that the frequency and relevance of such pathways are basically nil. Simply put, protein being converted to and stored as fat doesn’t happen to any appreciable extent in people consuming moderately more protein, even during a caloric surplus. Only until theoretical extremes (both in terms of calories and protein intakes) are reached, for weeks on end (>8 weeks), will you (potentially) see any significant effect of excess protein intakes on fat gain. Yea, a lot of ‘ifs’ and ‘maybes’ in that sentence.
In support of this notion, I looked at a well-controlled study (and I mean well-controlled!)  which saw no further increases in fat mass in subjects consuming 140% of their caloric needs alongside higher protein diets (15% or 25%) for 8 weeks compared to individuals consuming similar caloric intakes (i.e. 140% over caloric needs) with lower percentages of calories from protein (5%). Despite being a tightly-controlled metabolic ward study wherein participant’s activity and food intakes (amongst a whole other array of factors) could be monitored, what this study failed to do was look at the effects of a hypercaloric, high-protein diet(s) on bodyweight/composition in conjunction with a structured resistance training program in highly trained individuals; which brings me to today’s study.
Antonio et al. 2014
In this investigation, Antonio et al.  took a group of well-trained individuals (almost a decade’s worth of weight-training under their belts; no newbie gains here!) and randomized them to either their normal diet, lower in protein (control; average intake ~1.9g/kg/d or ~150g/d) or their normal diet, higher in protein (HP; 4.4g/kg/d or ~307g/d; achieved via protein supplementation) for 8 weeks. Both groups also maintained their usual training routines/volumes which were not significantly different from each other throughout the study period.
Body composition was measured via BodPod (much better than BIA but not as accurate as DEXA) and food/protein intakes were measured via food diaries (either hard copy or by using the MyFitnessPal© app). Training was also recorded (sets, reps, weight used) throughout the study period. So what did the investigators find?
Results & conclusions
They found that, despite increasing their caloric intakes by ~800kcals/d compared to the control group which actually decreased their caloric intake over the study period, and consuming protein intakes that were 5 times higher than the current RDA (0.8g/kg) and >2 times higher than the control group’s intake (~1.8g/kg), there was no significant difference in body composition between baseline and post-intervention time points, nor were the two groups significantly different in any other respect (Table 2 below; taken from Antonio et al. ).
In reality, the high-protein group actually increased their lean body mass while slightly decreasing their fat mass (control groups increased both), although to non-significant degrees. In line with the Bray et al.  study that I talked about previously (pick your link), it does not appear that high/excessive intakes of protein result in significant fat gain compared to lower, more realistic intakes (in this case, realistic for active, weight-trained individuals, i.e. ~2.0g/kg/d). I should note, however, that the Bray et al. study and the current study do differ in methodology (metabolic ward vs free-living, respectively) and study populations (middle-aged, healthy but sedentary individuals vs. highly-trained individuals, respectively). Nonetheless, the theme remains the same; excess protein under most conditions, even those where protein consumption is increased beyond the theoretical performance benefits while in the face of a mild caloric surplus, does not lead to excess body fat storage/gain. So, while we do possess the metabolic pathways to convert protein to fatty acids, again, this just doesn’t happen in real life situations.
Until next time!
- Bray GA, Smith SR, de Jonge L, Xie H, Rood J, Martin CK, Most M, Brock C, Mancuso S, Redman LM: Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial. JAMA 2012, 307:47-55.
- Antonio J, Peacock C, Ellerbroek A, Fromhoff B, Silver T: The effects of consuming a high protein diet (4.4g/kg/d) on body composition in resistance-trained individuals. JISSN 2014, 11.