Some background
To quickly recap in the case that you’re a little more novice, protein functions as a major building block for us physiologically. It plays a key role in our training recovery and repairing muscle tissue post-training, allowing us to get the most out of those sessions by placing us in a positive net muscle protein balance. In other words, protein ingestion stimulates muscle protein synthesis, which is essential for repairing and subsequently achieving the muscular adaptations we desire (muscle gain, strength gain, etc.).
For active individuals, it’s recommended to aim for anywhere between 1.5-2.0 g/kg/day. Recent studies have even stated a range of 1.8-2.5 g/kg/day in order to maximize muscle hypertrophy.
The “high protein” diet
There may be some discrepancies between what is or is not considered a “high protein” diet, as a high intake of anything, really, can be quite relative depending on the context. For the purpose of this discussion, I will be referring to the recommended intake that pertains to the athlete (1.8-2.5 g/kg) as a “normal” or baseline intake. It can also be argued that this range itself is “high” compared to the RDA’s recommendation of 0.8 g/kg/day, though the RDA’s recommendation is evidently inadequate for active and athletic individuals. The study to be discussed will take high protein to quite a new level!
The study
Not much research has been done to investigate overfeeding – specifically protein overfeeding. Protein is the most thermogenic of the macronutrients, allowing it to be more satiating since it takes longer for our bodies to break down and digest. With that said, it’s plausible to assume that more of a good thing equals better. Considering the benefits of protein in the diet, especially for the active and athletic populations, the question remains about how resistance-trained individuals will respond to such a drastic increase, or if an upper limit exists. Dr. Antonio and colleagues sought to get more clarity regarding significantly high protein diets.
Methods
Forty healthy, resistance-trained men and women were unequally randomized into a control group and a high protein (HP) group. The unequal randomization is simply due to the fact that the projected dropout rate of the subjects via lack of compliance or other later reasons. Regardless there are no significant baseline differences between the groups. The control group acts as a constant and was instructed to maintain their current diet and training regimen over the course of the study. Contrary to this, the HP group was instructed to consume 4.4 grams of protein/kg/day (well over 2x the evidence-based intake for the active/athletic). Food records were kept either via phone app (MyFitnessPal) or hand-written food diary. Whey and casein protein powder were used to supplement the HP group’s diet.
Key findings and considerations
Of the forty men and women who were recruited, thirty participated in the entirety of the 8-week study. These subjects have a few years of training under their belts, obviously making them more trained, which gives us some important insight into how dietary changes can impact the more intermediate and advanced lifters as opposed to those who are considered inconsistent or recreational trainees. This study is the first of its kind and considering it was done on well-trained, lean individuals alongside this, these results could vary depending on the activity level of the subjects.
After the 8-week study, the key outcome observed was that there were no significant body composition changes pre- and post-study (body measurements were done via Bod Pod), nor were there any changes seen between the two groups. Particularly regarding these body composition measures, no changes in body weight, fat mass, or fat free mass occurred in the high protein diet group. This is an incredibly novel finding in that this is the first study to report a hypocaloric high protein diet that had no impact on body composition (especially fat mass). Additionally, there were no significant changes in any of the variables studied for the control group.
More protein doesn’t equal more lean body mass
As for training, over the course of the 8 weeks there were no differences seen in training volume. Now, the ‘laissez-faire’ approach to training is worth noting as it can act as a weakness here due to the fact that it creates another variable that goes uncontrolled. For example, if training isn’t ideal or where it should be to induce muscular adaptations, nothing substantial will come from it. In contrast, having the experienced trainees participate in the study plays to this study’s advantage in a sense that we can trust them a bit more with their own training and activity level. Antonio and colleagues did not fail to mention the lack of a structured training program and possible changes had one been included.
Regarding the diet, the only significant change found was an increase in the total energy/caloric intake and total protein intake for the high protein group. It’s worth noting that whey protein and/or casein supplementation was practically necessary for the high protein group, otherwise it would’ve likely been unrealistic for them to obtain the 4.4 grams/kg/day of protein (the average intake being 307 grams per day).
What does this all mean and why does it matter?
As a former student of Dr. Bill Campbell, he would often say, “if you’re going to overeat, overeat on protein,” and prior to these results it sounded like pretty interesting advice. The high protein group consumed over 800 extra calories per day compared to the control group. When we think about this in the context of “calories in versus calories out,” this seems contrary to what we’d assume would happen and challenges the notion entirely. A calorie isn’t just a calorie anymore. And while more protein doesn’t equal better, it won’t necessarily hurt us either.
There’s the chance this result is partially attributed to the high thermic effect that protein has, but there are additional variables at play that make any kind of determination challenging. Some of those points to keep in mind include both the decision to let subjects handle their own training for those 8 weeks, as well as the highly trained population being studied (as opposed to sedentary or a general population). Lastly, overfeeding protein isn’t shown to produce any body composition changes – including even lean body mass – so this would demonstrate that perhaps an upper limit could exist for our protein intake, although it doesn’t show any detriment either.
Overall, like with any area of study, we simply need more research done in this area and cannot speak in absolutes. There are plenty of moving parts we can still tinker with to get a better picture, so we can only interpret these findings so much. So, no, this is not saying you need to eat even more protein than you already do, nor will I encourage intentional protein-overeating just for the heck of it, but this gives us the first of what I’m sure is many valuable insights into protein and how we can potentially optimize what we have in place.
References
Antonio et al. Journal of the International Society of Sports Nutrition 2014, 11:19
By Gillian SanFillippo
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