Protein intake and muscle growth: it ain’t what we thought!

One of Mark Twain’s most famous quotes was that ‘It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.’ This quote is relevant in so many areas of life, and sports nutrition is no exception. Many health-conscious and performance-focused individuals have been limiting their maximum protein intake per meal to 25-30 grams in the belief that further protein would just be ‘wasted’. This belief is based on the assumption that the additional protein consumed over 30 grams would not further enhance muscle building or recovery, but instead simply be burned for energy.

Scientific support

These aren’t just lay beliefs or superstitions that athletes and coaches unknowingly perpetuated. This line of reasoning has been well supported by the scientific literature. In particular, a series of studies demonstrated that increasing protein dosing beyond around 30 grams per meal resulted in no further increases in protein synthesis^(1-3). Further, the excess protein consumed was just burned for energy – ie the additional protein was just wasted.

More importantly perhaps, these findings didn’t just remain hidden in obscure scientific journals; they formed the backbone of scientifically based nutrition recommendations that have spread throughout the sports performance community, as well as health and fitness communities [and indeed, reported in SPB – Ed]^(4-5). These recommendations were given at scientific conferences, during lectures by nutritionists and nutrition scientists, incorporated into textbooks, and incorporated into nutrition guidelines. To all intents and purposes, it was considered ‘fact’ that protein consumption per meal should be limited to 25-30 grams to optimize the efficiency of protein utilization.

Impractical practicalities

These recommendations had real life practical implications. Along with the protein content of meals, the importance of total protein intake was emphasized as well. Athletes were encouraged to consume 1.3-1.8 grams of protein per kilogram to meet their protein needs, and in some more extreme cases, intakes of 2.2 grams per kilogram were suggested. This obviously created a problem for the 100-kilogram athlete if they needed to consume 200 grams of protein while only consuming 30 grams of protein per meal. That’s 6-7 meals per day, and it can be difficult finding portable sources of protein that allow for such consistent and regimented consumption! These recommendations present significant logistical challenges for many athletes, even those who are full-time athletes.

Anecdotally, some athletes, particularly larger athletes with higher protein needs, chose to ignore these recommendations due to the impracticality of limiting protein consumption per meal. They consumed less frequent meals and much larger dosages of protein, and they did so while experiencing no ill effects. There was no loss of muscle mass, no loss of muscle strength, and no impairment in muscle recovery. You may have even done so yourself! These anecdotal observations were supported by the feeding behaviors of many animals where food was consumed much less frequently, also with no seeming ill effect. For some, this raised questions about the traditional recommendations.

Tools for the job

Bearing in mind the above, it’s worth pointing out that the ability to effectively conduct scientific investigations is limited by the methodological tools that are available at the time. Unfortunately, in many cases, it turns out the tools that were thought to be effective have limitations that weren’t appreciated. In other words, they were really suitable tools to carry out the investigation. Just like better microscopes and telescopes allow us to see with greater detail, the same applies to the tools used to study protein metabolism. The original studies (finding that 30g was the maximum protein utilization amount in one feeding) examined protein dynamics on a much shorter timescale due to the limitations of the available technology. So do these findings hold true when we investigate this subject using more modern methods, which can track protein metabolism over longer time periods?

Armed with new questions and new strategies, a group of Dutch researchers have sought provide some clarity in regard to how much protein can really be consumed at a given meal, and whether that protein can be used effectively⁽⁶⁾. These researchers wanted to know how protein dynamics might differ over longer periods of time, and whether higher dosages of protein are truly ‘wasted’, or whether we simply haven’t been measuring protein dynamics as precisely and as accurately as possible.

The research

The researchers recruited 36 healthy males that were actively training 1-3 times per week. The subjects received standardized nutrition the night before their trial, and then reported the lab in the morning without eating. During the trial, the subjects performed an exhaustive 60-minute resistance training bout. Upon completing the bout, the subjects consumed 1 of 3 different drinks:

·       Drink containing 0 grams of milk protein

·       Drink containing 25 grams of milk protein

·       Drink containing 100 grams of milk protein

The milk protein incorporated radioactively labelled amino acids (the building blocks of proteins), so that that the scientists could ‘track and trace’ the amino acids to determine their fate. Would they be excreted, would they be incorporated into muscle tissue, or would they be used for some other purpose? The scientists measured the amino acid levels of the blood, and the level of amino acid enrichment. Tissues were analyzed, protein synthesis rates were measured, and plasma protein levels were measured.

In short, the scientists did everything they could to determine what happened to protein when it was ingested following a resistance training bout. If the subjects consumed 25 grams as opposed to 0 grams, or 100 grams as opposed to 25 grams, something is going to happen to that protein, and the scientists wanted to ensure they covered as many possibilities as possible to avoid making false assumptions about the fate of the amino acids.

What they found

The results were powerful. The high (100g) dose of protein led to a marked increase in the amount of amino acids in the blood. Importantly, these higher levels of amino acids were prolonged and they remained elevated for hours. This increase in elevated amino acids levels resulted in prolonged levels of protein synthesis. In other words, proteins were being built as a direct result of the elevated levels of amino acids in the blood (see figure 1). These amino acids weren’t being wasted, they were used.

Figure 1: Study results