Schoenfeld and Aragon published this paper just this morning in the JISSN, seeking to draw evidence-based conclusions for the maximum amount of protein that can be utilized for lean tissue-building purposes in a single meal for those involved in regimented resistance training. These guys put out so much great research, and also write with a style of great clarity.
Let’s begin with some exposition.
Previously, it has been suggested that muscle protein synthesis(MPS) is heighten after ingesting around 20-25g protein. This is in reference to healthy young males as concluded by Morton, McGlory, and Phillips (2015).
When you eat a foodstuff, it travels into the gut to be digested. Digestion is the catabolic process of foodstuffs being moved through the body by many sub-processes which ultimately leads to absorption or excretion as waste. Absorption, in a general sense, “…is the passage of nutrients from the gut into systemic circulation. Based on this definition, the amount of protein that can be absorbed is virtually unlimited.” Instead, what we are concerned with is that amount of protein that can be absorbed and then utilized for MPS. Protein metabolism is demonstrated very superficially in the flow chart below.
In agreement with our previously mentioned review of a paper on BCAA’s (found here), “…evidence shows the potential for competition at the intestinal wall, with AA that are present in the highest concentrations absorbed at the expense of those that are less concentrated.” This again demonstrates the superiority of ingesting whole, complete protein sources rather than BCAAs or EAAs independently.
There may be numerous factors that influence dietary protein metabolism including “…the composition of the given protein source, the composition of the meal, the amount of protein ingested, and the specifics of the exercise routine.” On a more individual basis, there may additional influence from “…age, training status, and the amount of lean body mass also impact muscle-building outcomes.”
Key Data on Protein Metabolism
Some literature has suggested that MPS is greatest when consuming whole protein regularly throughout the day. Areta et al. (2013) observed “…MPS was greatest in those who consumed 4 servings of 20 g of protein, suggesting no additional benefit, and actually a lower rise in MPS when consuming the higher dosage (40 g) under the conditions imposed in the study.”
When comparing different whole protein sources, “Whey is a “fast-acting” protein; its absorption rate has been estimated at ~ 10 g per hour. At this rate, it would take just 2 h to fully absorb a 20-g dose of whey.” Previous research has suggested that there is a certain level of oxidation that occurs naturally when AAs are in circulation, lowering net protein balance for those sources absorbed at slower rates. “For example, cooked egg protein has an absorption rate of ~ 3 g per hour, meaning complete absorption of an omelet containing the same 20 g of protein would take approximately 7 h, which may help attenuate oxidation of AA and thus promote greater whole-body net positive protein balance”
Some papers have shown greater anabolic effects from whey vs slower digesting proteins. “However, the majority of these findings were during shorter testing periods (4 h or less), whereas longer testing periods (5 h or more) tend to show no differences between whey and casein on MPS or nitrogen balance.”
When we pair these slower digesting proteins (such as casein) with carbohydrates, the absorptive rates are further lengthened, “…but still did not impact muscle protein accretion compared to a protein-only condition.” We can therefore conclude that pairing certain proteins with other macronutrients may delay/lengthen the absorption process but will not have a significant effect on muscle anabolism.
One study from Macnaughton et al. (2016) gave two different amounts of protein to trained males after a whole-body resistance training session and thereby “…showed that the myofibrillar fractional synthetic rate was ~ 20% higher from consumption of the 40 g compared to the 20 g condition.” These results were not well supported when Moore et al. (2009) found “…no statistically significant differences in MPS between provision of a 20 g and 40 g dose of whey in young men following a leg extension bout, although the higher dose produced an 11% greater absolute increase.” It seems that the greater musculature trained from a whole-body session may have been a key factor in stimulating MPS, rather than only lower extremity musculature.
We may then wonder how insulin levels may affect anabolism, as it has previously been labeled an anabolic hormone. Despite this label “…its primary role in muscle protein balance is related to anti-catabolic effects. However, in the presence of elevated plasma AAs, the effect of insulin elevations on net muscle protein balance plateaus within a modest range of 15– 30 mU/L.” This would suggest that greater insulin levels do not seem to correlate with greater MPS, but rather modest levels help guard against muscle tissue degradation.
When comparing pre- and post-workout protein intake, we may consider that “Wilborn et al., found no difference in lean mass gains after 8 weeks of pre- and post-resistance exercise supplementation with either whey or casein.”
First, we should try to (though difficult) consider potential differences between the acute responses from one meal vs the serial responses from numeral meals in a day vs the chronic adaptions of a long-term nutritional strategy. Findings have been inconsistent, and difficult to pursue.
Data from Morton et al. (2015). Suggests that “… 0.4 g/kg/meal would optimally stimulate MPS. This was based on the addition of two standard deviations to their finding that 0.25 g/kg/meal maximally stimulates MPS in young men.” In agreement, Moore et al. (2015) estimated that “…the dosing ceilings can be as high as ~ 0.60 g/kg for some older men and ~ 0.40 g/kg for some younger men.”
What about fast vs slow digesting protein sources? “It seems logical that a slower acting protein source, particularly when consumed in combination with other macronutrients, would delay absorption and thus enhance the utilization of the constituent AA.”
When we consider daily dosages, a recent meta-analysis on trained subjects “…reported an upper 95% confidence interval (CI) of 2.2 g/kg/day. Bandegan et al. also showed an upper CI of 2.2 g/kg/day in a cohort of young male bodybuilders.” Although there is reliable data that suggests greater concentrations of protein (> 20 g/meal) may result in greater circulating AA oxidation, this is circumstantial since some AAs will be used for tissue building. “It is therefore a relatively simple and elegant solution to consume protein at a target intake of 0.4 g/kg/meal across a minimum of four meals in order to reach a minimum of 1.6 g/kg/day – if indeed the primary goal is to build muscle”
Take-home Point: Schoenfeld and Aragon provide data which shows that it may be best to shoot for of 0.4 g/kg/meal, consuming a minimum of four meals/day, reaching 1.6 g/kg/day to promote anabolism. The upper CI’s show that a strategy to maximize anabolic responses are approximately 0.55 g/kg/meal, for a minimum of four meals a day, equating to 2.2 g/kg/day.
Less than a week ago, the Journal of the America Medical Association (JAMA), published a large RTC comparing the effects of a low-fat vs low-carb diet over the course of a year. Examine.com did a nice job reviewing the article (found here), closing with a Q and A featuring the lead author, Dr. Christopher Gardner. I would bet this ruffled some feathers for the extremists out there.
Subjects: Males and females were included with an average age of 40±7 years and a mean BMI score of 33. The two groups we split in a randomized fashion into healthy low-fat(HLF) (n=305) and healthy low-carb(HLC) (n=304).
Methods: For the initial two months, each group was instructed to aim for their lowest dosage at: HLC < 20 g/carbs/day and HLF < 20 g/fat/day. After three months, these values were not sustainable and mean values had risen to 96.6 g/carb/day and 42g/fat/day. Only a small number of HLC subjects were able to stay < 50 g/carbs/day, a threshold previously identified to stay in ketosis.
No specific caloric requirements were given, but subjects were instructed to “…maximize vegetable intake … minimize intake of added sugars, refined flours, and trans fats; and … focus on whole foods that were minimally processed, nutrient dense, and prepared at home whenever possible.”Health educators met with each subject individually for 22 sessions throughout the course of the year, focusing on methods to achieve the lowest fat/carb intake that could sustainable.
There were also 12 random/unannounced dietary audits, reviewing the subjects’ dietary choices over the past 24 hours. In conjunction, respiratory exchange ratios were taken which identified the primary source of fuel at a given time (fat or carb); and blood lipid levels were analyzed. Other outcomes regularly measured included changes in body composition (assessed by DXA scan), cholesterol levels, blood pressure, fasting glucose and insulin levels, resting energy expenditure, and total energy expenditure
Subjects were then screened for 15 different genotypes: 5 assumed to do better with a low-fat diet, 9 assumed to do better with a low-carb diet, and 1 neutral genotype. Also, every 3 months subjects completed an oral glucose tolerance test to measure insulin production. This test was used as an attempt to link a diet’s influence on insulin sensitivity levels.
Results: “There was no significant diet-genotype pattern interaction (P = .20) or diet-insulin secretion (INS-30) interaction (P = .47) with 12-month weight loss.” The study showed a 21% dropout rate, ending with 481 participants- still a very nice size for a 12-month study. As expected, HLF significantly reduced saturated fat intake, meanwhile HLC reduced overall glycemic index. While both groups saw reductions in glycemic load, the decline was much larger in the HLC group.
The HLF group had lost 11.7 lbs (5.3 kg) and HLC group 13.2 lbs (6.0 kg); difference is not statistically significant nor clinically relevant (1.5 lbs / 0.7kg). Resting energy expenditure (REE) had decreased significantly from baseline for both groups (-66.45 kcals for HLF, -76.93 kcals for HLC), though there were no significant differences between groups.
Discussion: Ultimately, both dietary groups found similar results, showing that neither strategy is superior to the other. Caloric intake between groups was very similar, which we know is the primary driver of altering body composition. That being said, the HLC group did consume a bit more protein, averaging 13.5 g/day more than the HLF group. Weight change from an individual basis appears very similar for both diets when plotted. Numerous subjects had great success while few other did gain weight.
The suspected genotype organization showed no relevance, but future studies may be able to better evaluate genetic signatures in the future. This was true with insulin production alike, which also did not predict weight loss success or failure.
Dr. Christopher Gardner ended his Q&A with Examine.com by telling readers to focus on 4 fundamental points when dieting:
- More whole foods
- More vegetables specifically
- Less added sugar
- Less refined grains
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