Some sports nutrition experts recommend a 60/20/20 diet. What’s that? It’s a diet where you get 60 percent of your daily calories from carbohydrate and 20 percent each from fat and protein. Advocates say endurance athletes need to consistently maintain this ratio of the three so-called “macronutrients” to perform optimally in training.

Other experts recommend a more evenly balanced 40/30/30 diet. And still others promote different ratios. But while they may disagree on the specifics, all of these experts agree that there exists some perfect balance of macronutrients that optimizes endurance training performance.

Guess what? They’re all wrong.

“Percentages are meaningless, because it is the absolute amount of carbohydrate and protein that matters,” says Asker Jeukendrup, PhD, an exercise physiologist at the University of Birmingham in England and one of the world’s leading experts on the effects of different amounts of carbohydrate and protein intake on endurance performance. “How much you need depends on your goals and the amount of training you do.”

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In other words, what matters is not the relative proportions of carbs, fat, and protein you eat but the basic quantity measured as total calories or grams. And since macronutrient needs vary depending on training volume, there is no single macronutrient ratio that could possibly meet the needs of every athlete.

So what are the right amounts? “Typically, carbohydrate needs will vary from 5 to 10 grams per kilogram of body weight per day with training ranging from one hour per day to five hours or more,” says Jeukendrup (editor’s note: 1 kg = 2.2 lbs).

Unlike protein and fat, carbs are not used structurally in the body — they are used strictly for fuel. Therefore the more active you are, the more carbohydrate you need, with the hardest-training athletes requiring twice as much carbohydrate as the lightest trainers. Studies have shown that athletes who fail to increase their carbohydrate intake sufficiently to match increases in their training volume do not perform as well.

Protein needs also vary with training volume, although somewhat less. Traditional recommendations call for one gram of protein per kilogram of body weight daily for recreational endurance athletes, increasing to 1.5 g/kg/day for serious competitors. But in a recent study, Jeukendrup found that going all the way up to 3 g/kg/day helped a group of elite cyclists to better handle the stress of an especially hard block of training. This is an extreme case, but it demonstrates that the carbohydrate and protein recommendations for athletes should be considered minimums. It’s OK and sometimes beneficial to get more, as long as doing so doesn’t cause you to consume too many total calories.

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And fat? Dietary fat needs are less sensitive to fluctuations in training volume. According to Jeukendrup, you can trust that your fat needs will be met if you get the right amount of carbs and protein and simply let fat account for the remainder of your daily energy needs.

Getting the right balance of macronutrients requires a little math, but it beats using a one-size-fits-all formula that doesn’t really fit all.

Daily Carbohydrate Needs

Training Volume (Hours/Day) Carbohydrate Needs
1 5 g/kg
2 6 g/kg
3 7 g/kg
4 8 g/kg
5 9 g/kg
>5 10 g/kg