Protein supplementation: myths vs. reality

Most active people and nearly all athletes understand that protein consumption is associated with muscle growth, sport, and performance outcomes. Understandably then, the popularity of protein supplements has followed suit for both athletes and non-athletes alike, particularly in the last 30 years. However, while the effectiveness of protein supplementation is automatically assumed, the actual research is actually much less clear.

While some positive outcomes have been found, plenty of less positive outcomes have been found as well, and the research is far from conclusive. This can be related to different study designs, types and amounts of protein, as well as different outcomes measured in the studies. This issue is further complicated by the fact that it’s comparatively easy to consume plenty of protein from the diet without resorting to protein supplements. Therefore, if an individual is consuming sufficient protein, more may not be helpful. So does protein supplementation lead to positive outcomes, and if so, what contextual factors are important? Let’s look at some new research and find out.

New research

A group of researchers from China sought to bring clarity to this topic by using meta-analytical techniques. This allowed them to comprehensively evaluate all the relevant protein supplement trials performed to date⁽¹⁾. Rather than performing a very large trial, the authors used statistical techniques to combine the result of many previous trials. Specifically, they were interested in analyzing ‘randomized controlled’ trials, as these studies are the most rigorous, including control and supplemental groups.

To further increase the rigor of the study, only trials involving athletes were included, where one group received supplemental protein and the other did not. In addition, the outcomes of the study were required to be related to athletic performance in some way. In short, all other trials were excluded from the analysis because the researchers wanted to focus on our specific population of interest (athletes) and our outcomes of interest (performance). In total, 75 studies were included for analysis.

What they did

When performing the analysis, the researchers analyzed the potential bias included in the studies. While scientific research aspires to be unbiased, it’s simply not possible to eliminate all bias in designed studies, which can arise due to technological, financial, or logistical challenges. For instance, if there was only so much money or time available for a given study, researchers may have to compromise the design of their study compared to what may have been ideal. While a study is not intentionally biased by the authors of included studies, it is still a factor that must be accounted for, especially when performing meta-analyses.

The authors also tried to account for publication bias. This is a bias towards published studies with positive findings whereas non-positive studies (ie the supplement didn’t work) can go unpublished. This information was used to assess the ‘quality’ of the findings. A study could find a very strong result, but if significant bias is present, the findings become uncertain.

The 75 studies included in the meta-analysis were designed differently, using different supplementation intervention and different outcomes. They used different types of protein and different amounts of protein, both of which could significantly affect the outcomes. Rather than simply asking ‘do protein supplements work?’ the researchers wanted to ask, ‘do certain types of protein supplements delivered in certain ways result in certain types of performance outcomes in certain situations?’ The latter is a much more nuanced question, requiring a more nuanced approach. They achieved this by making the following comparisons during the analysis:

• Athletic performance versus post-exercise recovery outcomes.
• Protein-only versus carbohydrate versus protein and carbohydrate versus placebo.
• Different types of protein (soy, milk, combined, etc).
• The amount of protein given in each supplemental dose.
• Total daily protein intake.
• When protein was ingested (day or night).
• Whether subjects consumed other foods before the supplement.
• If the control group received supplemental calories to match the protein group.
• Whether subjects served as their own control or not.
• Comparing acute versus long-term effects of supplementation.
• Looking only at endurance performance outcomes.
• Looking only at strength outcomes.
• Looking only at glycogen resynthesis outcomes (how much carbohydrate is stored in the muscle).
• Looking only at fatigue as an outcomes.
• Interactions between the above factors

In plain English, it’s not as simple as saying protein supplements ‘work ‘or ‘don’t work’ because whether that’s true or not may depend on all the circumstances above. By changing the interventions and by changing the outcomes, the results could be dramatically different.

What they found

When looking at endurance performance, a net positive effective of protein supplements was found. This was found for both aerobic and anerobic performance, particularly in cyclists. No effect was found for whole-body strength outcomes, although a positive effect was found when lower body strength was evaluated in isolation. As with strength, there was no overall effect found for fatigue-related outcomes, although there was a potential positive effective for ‘fatigue index’, a specific test used in cycling. There was no effect found for glycogen resynthesis.

When protein supplements were compared to a placebo, improvements in both endurance performance and muscle strength were found. When carbohydrate + protein supplements were compared to placebo, only improvements in endurance performance found. When protein supplements were compared to carbohydrate supplements, measures of glycogen synthesis were improved. The inconsistency of findings across different comparisons may therefore potentially weaken performance enhancement claims.

Ten different types of protein sources were evaluated. Only whey protein was found to have a positive effect, and that was for improving both endurance performance and muscle strength outcomes (see figure 1). No other protein sources yielded positive outcomes. Meanwhile, no positive outcomes were found for recovery with any type of protein source.

Protein dosages were grouped into three categories: 0–1 grams/kilogram of body weight, 1–2 grams/kilo, and 2–3 grams/kilo. Interestingly, only the lowest dose - 0–1 grams/kilo - was found to have a positive impact (endurance performance) and fatigue index. Further analysis demonstrated that 1 gram per kilo of supplemental protein improves athletic performance more than 1.5 grams/kilo, and for post-exercise recovery, 0.5 gram/kilo dose was more effective than 1 gram/kilo. The clear implication here therefore is that more protein is not better!

For total daily protein intake, 2 grams/kilo per day led to improved performance and recovery as compared to 1 gram/kilo per day, indicating that total dosage does matter, not just the supplemental dose (see figure 2). When protein was consumed was important as well; daytime supplement consumption seemed to have a positive impact on endurance performance whereas nighttime consumption did not.

When comparing energy-matched intake (supplementing protein but keeping calorie intake constant but reducing calories from carbohydrate and fat intake) to energy-unmatched (giving extra protein calories without cutting back other calories) supplementation, only energy-unmatched supplementation had a positive effect on endurance performance and muscle strength. This finding may indicate that the protein supplements are simply providing more energy rather than nutrients with a particular effect. Protein supplementation also had a positive impact on performance only when subjects consumed the supplements after consuming other food, and not when consuming the supplements in a fasted state.

Endurance performance was improved both acutely and chronically as a result of protein supplementation. This was not true of any other outcome measures. Further analysis indicated 40 to 65 days of increased protein intake is optimal for enhancing athletic performance. Deeper analysis also revealed that if the goal is to promote post-exercise recovery, 40 to 80 days of supplementation may be more appropriate.

Finally, it’s important to assess the reliability of these conclusions, which was determined by the following factors: sample size, meta-analysis results, and quality assessment, including risk of bias and result inconsistency.  Due to inconsistency and variation in the findings, the quality was rated ‘low’ for endurance performance. It was rated ‘very low’ for muscle strength and recovery for the same reasons and due to small sample sizes. While positive outcomes were found, they were only found in certain situations, and the findings were not particularly strong. Thus, some caution must be taken in changing behaviors as a result of the study.

Figure 1: Effect of whey protein vs. other proteins