You鈥檇 have a hard time finding any serious endurance athlete in 2025 who thinks protein doesn鈥檛 matter. Gone are the carb-centric days of pasta and Gatorade and nothing else. But figuring out how much protein runners, cyclists, and other endurance junkies actually need鈥攁nd when they need it鈥攔emains a work in progress.
I鈥檝e grappled with these questions a few times recently鈥攊n a piece busting some common protein myths, and in another discussing the idea of maximum protein intake. But now a in Sports Medicine, from a research team led by Oliver Witard of King鈥檚 College London, offers a comprehensive overview of the current state of knowledge. Witard and his colleagues focus on two key questions. First, how much protein do endurance athletes need on a daily basis to stay healthy and optimize long-term training adaptations? And second, what role can the tactical use of protein play in speeding up short-term recovery and boosting performance?
Protein for the Long Term
Government guidelines currently recommend getting at least 0.8 grams of protein per kilogram of body weight (g/kg) each day. For someone who weighs 150 pounds, that works out to 55 grams of protein. For reference, a standard 5-ounce can of tuna has about 20 grams of protein.
There are two main problems with this guideline, however. First, it鈥檚 intended to be the minimum required to stay healthy, not the optimal amount to maximize performance. Second, it was formulated using a measurement technique that involves tracking the amount of nitrogen being consumed and excreted from the body, which some scientists believe underestimates protein needs. A newer approach called the 鈥,鈥 which involves labeling one specific type of amino acid with a carbon isotope to see how quickly it鈥檚 burned, gives higher numbers and is also more practical for testing specific populations like athletes.
The usual argument for getting lots of protein is that it provides the building blocks鈥攁mino acids鈥攆or building new muscle. That鈥檚 important for strength training, but endurance athletes need it for other reasons. One is that these building blocks are used to repair the muscle damage incurred by hard training: the longer and harder you run, the more damage you incur, and more protein you presumably need for repairs.
During prolonged exercise, your body also starts burning amino acids for fuel. The amounts are generally small, and how much you burn depends on the nature of the exercise and what else you鈥檙e eating, but in some cases 5 to 10 percent of the fuel you need for a given workout is provided by protein. If you鈥檙e training hard, you鈥檒l need to eat extra protein to replace those losses.
There are some more subtle possibilities, too. Muscle isn鈥檛 the only part of the body that鈥檚 built from protein. One of the key adaptations athletes gain from endurance training is an increase in the amount of protein in the mitochondria, where cellular energy is generated. The more protein in the mitochondria, the more efficiently it creates energy. A few studies have sought to聽 figure out whether eating more protein boosts the mitochondrial response to exercise. The results so far haven鈥檛 been convincing, but it鈥檚 still an open question.
Witard and his colleagues pooled data from various indicator amino acid studies to assess protein needs for endurance athletes under various conditions. Here are some of the key numbers:
The indicator amino acid data suggests that even untrained people need about 1.2 g/kg of protein per day, 50 percent more than the FDA鈥檚 recommended daily intake of 0.8 g/kg. And endurance athletes need another 50 percent more than untrained people, with a level of 1.8 g/k/g ensuring that 95 percent of people are getting all the protein their bodies can use. In comparison, using the same indicator amino acid method find that resistance-trained athletes need somewhere between 1.5 and 2.0 g/kg per day, raising the possibility that endurance athletes might actually need more protein than lifters.
There鈥檚 an important point to bear in mind, though: endurance athletes also tend to eat a lot more than the average person, which means they automatically get more protein. among American adults averages 1.25 g/kg for men and 1.09 g/kg for women, pretty close to the overall target of 1.2 g/kg for untrained people. In comparison, found that endurance athletes average 1.4 to 1.5 g/kg鈥攏ot quite at the 1.8 g/kg level, but not that far away.
There are some other nuances in that graph. Data on male-female differences is very sparse, but there are some hints that women might require more than men relative to their body weight. That might be particularly true during the luteal phase of the menstrual cycle, since progesterone can affect protein burning. Witard and his colleagues make a blanket recommendation that both male and female endurance athletes should aim for 1.8 g/kg, but they throw in the speculative possibility that females 鈥渕ay consider鈥 upping it to 1.9 g/kg during the luteal phase of their cycle.
Short-Term Protein Tactics
The big surprise in the data above is that endurance athletes seem to use more protein on their rest days than on training days. This finding has popped up in , and it鈥檚 definitely not what the scientists were expecting. It鈥檚 possible that there鈥檚 some quirk of metabolism that鈥檚 skewing the measurements used to assess protein needs when you try to compare exercise and non-exercise days.
But it鈥檚 also possible that the effect is real鈥攖hat when you give your body a break, its repair and adaptation mechanisms kick into overdrive and thus use more protein than usual. If this is true, it鈥檚 an argument for upping your protein intake on rest days: Witard and co. suggest aiming for 2.0 g/kg. And on a more fundamental level, it鈥檚 an argument for including true rest days in your training program periodically, since they seem to trigger recovery processes that don鈥檛 happen on normal training days. At this point, I鈥檇 say the jury is still out on whether the effect is real.
Either way, the researchers suggest aiming for 0.5 g/kg of protein following exercise to help repair any muscle damage incurred during the workout. For a 150-pound person, that鈥檚 34 grams of protein, which is what you鈥檇 get in a substantial meal with a good protein source. How soon is 鈥渁fter exercise鈥? I don鈥檛 think there鈥檚 any convincing data that says it has to be immediately after. Your next meal is fine鈥攗nless your workout was after dinner and you鈥檙e planning to head to bed, in which case you should make a special effort to get some protein in.
The data also suggests that athletes use more protein when they鈥檙e training in a carbohydrate-depleted state. In this case, we鈥檙e not talking about a consistently low-carb diet, but rather doing certain training sessions in a low-carb state to help the body adapt to burning fat more efficiently. There鈥檚 decent evidence that protein can help power these workouts, and Witard suggests taking in 10 to 20 grams of protein before and/or during this type of session.
This idea of using protein to compensate for low carbs also connects to one of the most hotly debated ideas about protein for endurance athletes. There have been various research-backed claims over the years that adding protein to a sports drink that you consume during a race or training session will enhance your performance, and that taking in some protein in the immediate post-workout window will speed up the rate at which you refill the carbohydrate stores in your muscles.
All these claims, Witard and his colleagues argue, are the result of studies where the subjects didn鈥檛 get enough carbohydrates. If you鈥檙e meeting your carb needs, adding protein to a sports drink will neither boost your performance nor accelerate your muscle refueling. There may be exceptions for ultra-endurance events, which haven鈥檛 been well-studied and have somewhat different metabolic challenges compared to a marathon. But the researchers鈥 final conclusion is a reminder that for endurance athletes, despite protein鈥檚 current popularity, carbohydrate is still king.
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