The more you run and train, the more critical your diet becomes. From preparing food to making sure you get enough of the calories you need at the right time, it’s a constant source of preoccupation.

But what about what you eat? Everyone wants to find the secret-sauce combination to perform and feel their best. The list of possible diets is long: high fat, low fat, primal, keto, Paleo, high-protein and vegetarian—just to name a few! Plant-based diets, long promoted for political and ethical reasons, are also taking hold with endurance athletes. It’s not that runners are protesting on the run—many say avoiding meat and less healthy fat makes them perform better.

Vegetarian diets have an impressive array of medical benefits: reducing the incidence of stroke and cardiovascular disease, lowering cholesterol and reducing the risk of cancer. They’re also anti-inflammatory, which while helping to reduce chronic diseases, may also help athletes perform at a higher level.

Matt Frazier was more than six years into his quest to qualify for the Boston Marathon, and had reached a plateau. In 2009, he decided to go vegetarian and started No Meat Athlete to chronicle his journey. Six months after going vegetarian, Frazier earned his BQ.

“I became a vegetarian for ethical reasons, and my body responded well to it,” says the Asheville, N.C., resident, who eventually became vegan and now races 50- and 100-mile ultras. “I think the anti-inflammatory aspect is a big piece of the success of vegan diets for athletes. There is also the nutrient-density aspect. You are getting a lot of micronutrients per calorie.”

Frazier says that besides the need to plan ahead with food choices, something he learned the hard way by being a little hungry after his first ultra, training and racing as a vegan isn’t difficult. It’s forced him to make informed decisions about food and be more methodical with fueling as he trains so that he can experiment with what works best for him. Bananas, oranges and dates are his go-to fueling options for shorter runs. When it comes to multi-hour, ultra-distance runs, he snacks on things like refried beans on a tortilla or a pita with hummus.

Sage Canaday, a 31-year-old professional ultrarunner and marathoner from Boulder, Colo., has been a vegetarian since birth and also credits the nutrient- and antioxidant-dense aspects of a vegetarian diet for its success.

“You get a lot of nutrients per calorie,” says Canaday, who owns a 2:16:52 marathon PR and numerous trail running records. “By the time you’ve consumed the calories you need, you’ve also consumed a lot of vitamins, nutrients and antioxidants. Plant-based eating is also hydrating, which is good for your body.”

Basically your body has to do less work to get what it needs from food. Canaday, who considers himself to be 99 percent vegan, also touts the benefits of the higher fiber level in a plant-based diet compared to a traditional carbohydrate-rich way of eating.

Frazier admits that when he first became a vegan, he ate a lot of “vegan junk food.” It’s an understandable crutch as people switch to something new and less familiar, like a whole-foods diet. But high-quality calories are essential. He emphasizes the importance of focusing on vegetables, fruits, nuts, seeds, healthy fats and whole grains to feel your best.

Concerns about vegetarian and vegan diets for athletes stem from the ability to get enough protein and other nutrients, many of which are associated with meat. Both Canaday and Frazier say that as long as you eat a variety of plant-based foods and whole grains, getting enough protein isn’t a problem. And neither athlete relies on protein powder supplementation. However, getting enough vitamin B-12 is a legitimate concern. A simple blood test will let you know if you have enough; if not, it’s easy to supplement. Frazier also said vitamin D may be an issue, but, again, supplementation is simple.

A recent study from Arizona State University found that not only does a vegetarian diet not hinder athlete performance, if may help with aerobic capacity. But is it sustainable?

“For longer term sustainability, I don’t want to pretend that a vegan diet has everything you will ever need, but supplementation should solve the problem of any deficiencies,” says Frazier, whose second book, The No Meat Athlete Cookbook, was released in May.

As with any diet, it depends what works best with your body. Also understand that your body and its needs may change over time.

When asked about the sustainability of a vegetarian or vegan diet for athletes, Canaday is more confident.

“I think you can thrive on it.”