There has always been a big gap between the official recommendations for how much protein we “need” and how much strength athletes have consumed. Endurance athletes haven’t paid much attention to this debate; you don’t need big biceps to run a good marathon, after all.
But a new study from Daniel Moore and his colleagues at the University of Toronto and Japan’s Ajinomoto Co. offers a revised take on the question. The data was presented at the American College of Sports Medicine’s annual meeting earlier this month in Boston, and has now been published in the journal PLoS ONE.
The key development is that the study uses a relatively new technique called “indicator amino acid oxidation” to measure protein use, which involves tagging an amino acid with a carbon isotope tracer to allow its use in the body to be tracked. Previous studies have generally relied on a technique called “nitrogen balance,” which is more cumbersome and - according to the authors of the new study, at least - less reliable.
The study involved six distance runners who reported typical weekly mileage of between about 30 and 80 miles. Over a three-day period, they consumed a standardised diet and ran 10K on the first day, 5K on the second day, then a 20K time trial on the third day. After the 20K run, they consumed a randomly assigned amount of protein (each subject repeated the whole protocol as many as seven times) along with a standard amount of the marked indicator amino acid. By analysing the pattern of how much of the marked amino acid was consumed in different trials, the researchers could determine whether a given dose of protein was enough to meet the body's needs (for more details of the method, see this paper).
The results indicated that the subjects needed an average of 1.65 grams of protein per kilogram of body weight per day to provide the amino acids required for muscle repair and synthesis, leading to a “recommended” intake of around 1.8g/kg/day. That’s higher than both the recommended dietary allowance of 0.8 g/kg/day for non-athletes, and the typical 1.2 to 1.4g/kg/day recommendation for endurance-trained athletes.
Why do endurance athletes need more protein? One possibility is that they’re burning it during the run: previous studies suggest that about 5 percent of the energy you burn during exercise comes from oxidising protein, and that can rise to 10 percent if your muscles are low on glycogen (as they would be late in a 20K time trial). That could account for an additional 0.2 g/kg/day or so in the current study.
Protein is also needed to repair and remodel tissue - not just the muscle you directly damage while running, but also other damaged areas of the body like the gut. In that respect, high-impact activities like running may trigger greater protein needs than lower-impact activities like cycling or swimming.
So are you protein deficient? Probably not. A typical North American diet provides somewhere around 1.6g/kg/day, and hard-training runners generally get more than that simply because they’re eating more in general. That said, there are certainly some runners who focus on carbs (or, these days, fat) and neglect protein.
If anything, what most of us need to pay more attention to is distributing our protein throughout the day rather than concentrating most of it at dinner. A typical pattern is 10 to 15 grams of protein at breakfast and lunch, then 65 grams at dinner. But the body can make optimal use of only 20 to 30 grams at a time, so it’s better to spread the protein out into at least four doses - including, for example, a pre-bed high-protein snack.