Alex Morgan remembers athletes sporting milk mustaches in ads when she was a kid, reinforcing the idea that she needed protein from animal and dairy products to be strong.

“I never thought it was possible I could be playing at an elite level as a professional athlete with a plant-based diet,” the U.S. women’s soccer star told USA TODAY Sports. “Then I realized it wasn’t detrimental at all. What I learned growing up wasn’t all that true.”

When Morgan’s Orlando Pride teammates and the MLS teammates of her husband, Servando Carrasco, showed they could thrive while eating vegan, the stigma was erased and Morgan was ready to try a new diet. She became vegetarian in August 2017 and then took on a mostly vegan lifestyle at the beginning of 2018.

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“If anything, it makes me stronger and helps with fatigue and recovery,” said Morgan, who had the U.S. women team's chef, Teren Green, prepare vegan meals during the World Cup, prompting several of her teammates to give it a try.

Veganism is on the rise in the United States — the plant-based market increased 17% in dollar sales this last year, according to The Good Food Institute — and more athletes are turning to the diet, particularly at the peak and latter stages of their careers.

New England Patriots quarterback Tom Brady is the most prominent athlete to embrace veganism, crediting his mostly plant-based diet for allowing him to play at an MVP level into his 40s. He made the change starting in 2014, and detailed his approach in his 2017 book, "The TB12 Method."

Athletes have been exposed to plant-based diets for a variety of reasons. NBA guard Chris Paul said his children’s nanny was vegan. Recovering from a shoulder injury, Carolina Panthers quarterback Cam Newton said in April he’s gone vegan to aid his stamina and rehabilitation. Tennis star Venus Williams adopted a vegan diet in 2011 after she was diagnosed with an autoimmune disease. A gluten allergy led Wimbledon champion Novak Djokovic to go plant-based, and in 2016 he opened up a Monte Carlo vegan restaurant.

While most nutrition experts are in agreement that veganism aids recovery and promotes good health, others raise questions about its effectiveness and see the no-meat philosophy as limiting.

Yet athletes are among the biggest advocates for veganism. Morgan and Brooklyn Nets guard Kyrie Irving were named “Most Beautiful Vegan Celebrities” by PETA this summer.

"The rules aren't as strict as everyone thinks," Irving told USA TODAY Sports. “I’m an example of someone who ate really unhealthy — fast food or a quick TV dinner in the microwave — without educating myself on what I was putting into my body. Now I feel like I understand the truth — how certain chemicals in meat affect your body, and that now there are alternatives bridging the gap available.”

Those alternatives start with plant-based meat companies such as Beyond Meat, which has attracted Paul, Irving and Houston Texans wide receiver DeAndre Hopkins as investors.

“You’ve got to be open-minded,” Paul said. “I was someone who was like, ‘I don’t want that fake chicken or fake burger.’ But it tastes similar and it really makes a huge difference in how I feel.”

James Loomis, who practices internal medicine at Barnard Medical Center in Washington, D.C., said he believes a vegan diet is a natural fit for athletes: It “leads to quicker recovery from workouts and better injury prevention. The food pyramid is misleading and that’s stayed with us from a young age.

"The standard American diet leads to low-grade inflammation so when athletes are exercising it’s like putting Diesel fuel into a regular car.”

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However, veganism is not fully embraced by athletes or experts.

Cate Shanahan, a nutrition consultant for the Los Angeles Lakers, New York Yankees and Green Bay Packers, says plant-based meat is “toxic” and argues that the recovery boost athletes experience from the diets comes from removing “chips and soda, like any good diet.”

Shanahan instead believes animal meat on the bone and animal bone broth can bolster digestive health and relieve joint pain. She sees the keto diet — what Tim Tebow currently follows — as a healthy option because of its emphasis on using natural fats from butter and coconut as opposed to vegetable oils. She contends that a plant-based diet or the largely meat-based paleo diet are “limited.”

Several high-profile athletes tried vegan lifestyles before opting out. Portland Trailblazers guard Damian Lillard gave up his vegan diet because he lost too much weight.

“Veganism doesn’t pay attention to the culinary tradition of the world’s healthiest cuisines that kept our ancestors disease-free,” Shanahan said. “The healthiest diet comes from four natural pillars — fresh food, fermented and sprouted food, meat cooked on the bone, and organ meats.”

Loomis disagrees, and has data to prove it. He collaborated with experts for a 2019 study that outlined evidence of plant-based diets benefiting endurance athletes in heart health, overall performance and recovery.

“It’s a factual myth that we have to have animal protein to perform at a high level,” he said. “With plants, food becomes more like medicine.”

Loomis is one of the doctors featured on "Game Changers," a documentary set to debut in September that features MMA fighter James Wilks exploring the differences between protein from plant-based and meat-based diets.

“If you go into locker rooms and look at the pre-game meal, it’s usually steak or chicken or pasta, and there’s lots of Whey Protein powder,” said Loomis, the former team internist for the St. Louis Rams and Cardinals. “That’s then amplified commercially with marketing, basically saying, ‘You’re not a man unless you eat meat.’”

One example: NBA Hall of Famer Charles Barkley ranted on a Turner Sports broadcast this spring, “They’ve got a name for people who don’t eat meat: Damn fools.”

Still, times are changing. Brady appeared in a 2002 Got Milk? ad. Nowadays he's promoting his own plant-based protein shakes.

Silver medal-winning Olympic cyclist Dotsie Bausch became vegan in her mid-30s — three years before the 2012 London Games — and appeared in an anti-milk commercial for her non-profit, Switch4Good, during the 2018 Winter Olympics.

"Most people have meat and dairy because the next person does it," Bausch said. "The truth is milk doesn't make you grow big and strong." .

The vegan stigma

Paul’s personal chef, Seong Hwang, prepared a post-game meal for the Houston Rockets last season. He didn’t tell players until afterwards that it was made with Beyond Meat.

“The players, the staff, they all loved it solely based on the taste,” Seong said. “No one wants to give up taste. Chris is a big foodie. If what I was making him didn’t taste good, he wouldn’t stick with it. Whenever you hear veganism, you think you have to give up something or eat tofu to survive. That’s really not the case.”

The vegan perception can be damning, though. According to a 2017 report by NBC Sports Bay Area, NFL teams were dissuaded by Colin Kaepernick’s then-vegan diet, calling it a red flag when considering signing the free agent quarterback.

“There’s a weird connotation that comes with veganism,” said Loomis, who moved his practice to Washington, D.C., from the St. Louis area because colleagues in the Midwest thought his approach was "crazy."

Morgan says the stigma can go both ways.

“It took me a while to feel comfortable with my lifestyle and not being a super-strict vegan,” said Morgan, who also supports veganism because of ethical concerns around animal rights. “The vegan community can be very unforgiving at times, and I don’t want to sit here and say I’ve never eaten dairy or worn leather. But I haven’t eaten meat in two years and do the best I can.

“I just want to feel good about why I’m doing this. I don’t think our country is there yet, in terms of being able to adopt a fully vegan lifestyle. We’re getting there.”