Health care professionals that warn cyclists and other endurance athletes away from vegan diets may be doing them a disservice, according to Dr. Michael Greger, founder of the science-based nonprofit NutritionFacts.org.

In a video, Dr. Greger refers to a 2020 study that found that “vegan athletes—even though they were significantly older—had significantly superior aerobic capacity and endurance, lasting 25 percent longer on a time-to-exhaustion cycling test. The question is: why?”

It could be that vegans generally have a high intake of carbohydrates, which could lead to better endurance through high muscle glycogen storage, the doctor surmised. Another possibility could be the anti-oxidant and anti-inflammatory nature of their diets, he said.

“Maybe it’s even their hearts,” Dr. Greger said. In a study showing superior VO2 max in vegan athletes, echocardiograms were conducted in real time using ultrasound. The lower relative wall thickness and better main ventricle systolic and diastolic functions in vegans could also be a contributor in high endurance, he said.

Or perhaps the vegan athletes were just better trained than those who followed a non-vegan diet? Nope. The weekly training frequency and distances studied in runners were similar in both groups, suggesting benefits even with the same amount of training.

“So, it’s important to educate healthcare professionals so they don’t try to discourage a vegan diet, and may even want to consider telling folks implementing an exercise training program to give it a try,” the doctor said. 

Vegetarian diets increased VO2 max in diabetics

In the video, Dr. Greger also pointed to research that shows VO2 max increased by 12% in a group of vegetarian patients with type 2 diabetes as compared to a group on a conventional calorie-restricted diet that showed no measurable improvement.

Researchers randomized the diabetics to the same caloric restriction, the same exercise, with the only difference being vegetarian versus nonvegetarian. Researchers provided all the meals so they could ensure compliance and closely monitor the exercising.

Maximal performance increased by 21% in the vegetarian group, significantly better than in the nonvegetarian group, which showed no significant improvement. 

“In other words, the results indicated that more plant-based diets led more effectively to improvement in physical fitness than less plant-based diets, after the same aerobic exercise program,” Dr. Greger said.

The research seemed to show that those eating vegetarian were better able to burn off carbohydrates compared to nonvegetarians, and had better insulin sensitivity––both markers of improved metabolic flexibility, meaning the ability to switch back and forth between burning sugar and fat, the doctor noted.

Benefits more than an improved VO2 max

“Besides physiological mechanisms, there may also be psychological factors,” Dr. Greger said.

The vegetarian group reported reduced hunger and reduced feelings of depression, which may have given them a more positive attitude toward exercise, he noted. 

 “Those randomized to eat vegetarian had a greater improvement in quality of life and mood,” Dr. Greger noted.  “They felt less constrained, meaning the calorie restriction didn’t seem as burdensome; they had less disinhibition, meaning less tendency to binge and overeat, along with maybe less feelings of hunger. Not to mention the superior effects of a vegetarian diet on body weight, glycemic control, blood lipids, insulin sensitivity, and oxidative stress.”

Simply eating meat-free led to around a six-pound weight loss in the vegetarian group. “Same calories, yet more loss of body fat. And not surprisingly, better control of their diabetes. All in addition to leading more effectively to improvements in physical fitness,” Dr. Greger said.

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The sources cited in the video are:

• Boutros GH, Landry-Duval MA, Garzon M, Karelis AD. Is a vegan diet detrimental to endurance and muscle strength? Eur J Clin Nutr. 2020;74(11):1550-5.
• Król W, Price S, Śliż D, et al. A Vegan Athlete’s Heart-Is It Different? Morphology and Function in Echocardiography. Diagnostics (Basel). 2020;10(7):477.
• Veleba J, Matoulek M, Hill M, Pelikanova T, Kahleova H. “A Vegetarian vs. Conventional Hypocaloric Diet: The Effect on Physical Fitness in Response to Aerobic Exercise in Patients with Type 2 Diabetes.” A Parallel Randomized Study. Nutrients. 2016;8(11):671.
• Kahleova H, Hrachovinova T, Hill M, Pelikanova T. Vegetarian diet in type 2 diabetes–improvement in quality of life, mood and eating behaviour. Diabet Med. 2013;30(1):127-9.
• Kahleova H, Matoulek M, Malinska H, et al. Vegetarian diet improves insulin resistance and oxidative stress markers more than conventional diet in subjects with Type 2 diabetes. Diabet Med. 2011;28(5):549-59.