Ultramarathoner Scott Jurek has some simple advice for those hoping to combine very high levels of physical activity with a vegetarian or vegan diet.
"The first thing to worry about isn't so much what you eat, but how much you eat," he told a reporter shortly before setting a U.S. record of 267 kilometres for the 24-hour run in 2010.
"You have to take the time to sit at the table and make sure your calorie count is high enough."
Mr. Jurek's remarkable athletic and dietary feats are currently in the spotlight thanks to the recent publication of his book, Eat and Run: My Unlikely Journey to Ultramarathon Greatness.
His athletic success – and his ability to consume 5,000 to 8,000 calories per day with no meat or animal products – makes him unique, but a growing body of research suggests that, with care, others can emulate his approach.
The most common criticism of plant-based diets for serious athletes is that it's difficult to get enough protein.
As Mr. Jurek points out, the basic challenge of getting enough boils down to taking the time and effort to eat enough protein-rich plant foods like spinach and lentils.
But there's also the more subtle question of protein quality. Research by McMaster University researcher Stuart Phillips and others has shown that dairy protein stimulates muscle synthesis most effectively compared to other types of protein, like that found in soy.
While this may not be a problem for vegetarians, vegans – who don't consume any dairy products – might consequently have a less-than-optimal response to strength training.
"It's not that plant-based proteins can't get the job done," Dr. Phillips says. "They can, but the concept of complementary proteins has to be followed."
This idea – that vegetarians need to combine proteins from different sources like grains and legumes at each meal in order to obtain "complete" proteins – has fallen from favour in recent years, but Dr. Phillips's research suggests that vegan athletes can still benefit from it, especially for post-workout meals.
Another issue is iron: though leafy greens like kale and spinach are excellent sources of iron, only about 10 per cent of iron from plant sources can be absorbed by the body, compared to 18 per cent from animal sources. Female endurance athletes, in particular, are prone to low iron levels, so they may need to consider iron supplements if tests show their levels are low. A 2010 review in the journal Current Sports Medicine Reports identified several other micronutrients that vegan and vegetarian athletes may be deficient in. Zinc, vitamin B-12 and the omega-3 fatty acid DHA are all crucial for physical performance and are either hard to absorb or hard to get enough of from plant sources, so the authors recommend taking supplements. For vegans, calcium may also be a concern with a dairy-less diet. Foods like bok choy and kale, as well as seeds and nuts, provide good sources of calcium that can be readily absorbed by the body, so they should be emphasized.
Vegetarians vs. omnivores
Relatively few studies have attempted to directly compare the performance of vegetarian and omnivorous athletes, but the results have generally been favourable. One in 1970 found no difference in lung function and thigh muscle size; another in 1986 found no difference in serum protein levels; and a 1989 study found no difference in finishing time for a 1,000-kilometre run.
"I don't think there is any evidence that a vegetarian or vegan diet is any 'better' or 'worse' for performance," says Asker Jeukendrup, a nutrition researcher and the global senior director of research for the Gatorade Sports Science Institute in Illinois, "but you will have to be much more aware of what you are eating."
That's a nearly universal piece of advice when people discuss plant-based diets for high-performance athletes – and perhaps it should be seen as an advantage rather than a disadvantage. To eat with more attention and greater mindfulness sounds like a good idea, whatever your dietary persuasion or athletic aspirations happen to be.
Alex Hutchinson blogs about research on exercise at sweatscience.com. His latest book is Which Comes First, Cardio or Weights?