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The favoured fuel of the long-distance runner is carbohydrate – and true to that cliché, Krista DuChene loads up on carbohydrates such as pasta and rice in the days before big events like the one in Rio de Janeiro next Sunday, when she and teammate Lanni Marchant will become the first Canadian women in two decades to compete in an Olympic marathon.

But don't assume that's what her dinner plate looks like all the time.

"Protein is very important for runners," says DuChene, a 39-year-old mother of three who works as a registered dietitian in Brantford, Ont., when she's not running. From the protein powder she adds to her oatmeal in the morning to the cottage cheese she eats before bed, DuChene is a staunch believer in getting enough protein to manage her appetite and fuel her recovery from training.

In fact, protein is more important for runners and endurance athletes than once believed, according to new research by University of Toronto professor Daniel Moore and collaborators at Japan's Ajinomoto Co. Their latest study, based on a new experimental technique, suggests that runners need as much as twice the current recommended daily amount for sedentary adults – and, according to DuChene and other experts, when you eat, your protein may be as important as how much you get.

The new results, which were published in June in the journal PLOS One, relied on a technique called "indicator amino acid oxidation," which involves tagging a component of protein with a carbon isotope tracer so that it can be tracked in the body. This approach is an alternative to previous methods of calculating protein requirements that, according to critics, underestimated actual protein needs.

The researchers recruited six athletes whose typical training involved running between 45 and 130 kilometres a week, and put them through a series of three-day protocols that involved running 10 kilometres on the first day, five kilometres on the second day and 20 kilometres on the third day, at which point they consumed varying amounts of protein marked with the isotope tracer.

The results suggested that, on average, the subjects needed to consume 1.65 grams of protein per kilogram of bodyweight per day simply to break even. To build in a safety margin for individual variations, the resulting recommendation was that endurance athletes should aim for about 1.8 grams of protein per kilogram – in sharp contrast to the recommended dietary allowance of 0.8 g/kg for sedentary adults and previous recommendations of 1.2 to 1.4 g/kg for endurance athletes.

Given that marathoners don't tend to sprout a lot of extra muscle, where does all this protein go?

Some of it may simply be burned during training. Even though carbohydrate and fat provide most of the energy for prolonged exercise, previous studies have found that burning protein contributes 5 per cent to 10 per cent of the energy needed – enough to account for an additional 0.2 g/kg/day in the athletes studied.

More importantly, even if you're not trying to build bigger muscles, protein provides the key building blocks – amino acids – for repairing and rebuilding the muscle you've got after the rigours of training. Some types of training, such as downhill running, produce particularly high levels of muscle damage that requires repair.

Taking in protein may also help speed up postexercise rehydration and help your muscle restock their fuel stores more quickly, as well as bolstering your immune system during heavy training, though more research is required to confirm these benefits.

So is there an epidemic of protein-starved endurance athletes across the country? Probably not. The typical Canadian diet contains plenty of protein, and hard-training athletes get more than average since they eat more over all. Still, earlier studies have found that about 10 per cent of male endurance athletes and 20 per cent of female endurance athletes were failing to hit even the former minimum recommendations.

"To be honest, I rarely have to counsel athletes on including more protein in their diet," says Nicole Springle, a sports nutritionist with the Canadian Sport Institute Ontario who will be working with athletes in Rio. "Ninety-five per cent are getting well above the recommended amount when you look at their daily totals. It's usually more focused on the timing."

That's because your body can only make optimal use of a limited amount of protein – typically about 20 to 30 grams, the equivalent of half a can of tuna – at once. Since we tend to cram in more than half of our daily protein at dinner, we're missing opportunities to trigger accelerated muscle repair and growth at other times.

For DuChene, in addition to her morning protein powder and evening cottage cheese, that means meals with eggs, fish and lean meats, and snacking on nuts and nut butters, yogurt and milk to spread her protein intake throughout the day. She also drinks a protein-rich recovery drink after long training sessions.

In the end, most of us – even the leanest endurance fiends – probably get enough protein to satisfy our minimum requirements. But if, like DuChene, you're looking for the optimum rather than the minimum, the new research suggests it may be worth adding meatballs to that mound of pasta.