Her US Open dreams were cut short. But Madison Keys is already planning her comeback — fueled by more calories and seriously intense training.

• US tennis player Madison Keys, who won the Cincinnati Masters in 2019, recently competed in the US Open.
• Keys said her diet and recovery during competition season included simple, high-protein meals.

Knocked out early at the US Open, American tennis star Madison Keys is already preparing for a tough competition schedule next year.

The 2019 winner of the Cincinnati Masters, one of the most prestigious tennis tournaments in the US, Keys lost to fellow American Coco Gauff in the third round of the US Open earlier this month.

Though the world of sports is awash with cutting-edge health and wellness innovations worth millions of dollars, Keys says her prep doesn't involve fancy recovery technology and a strict diet. The 27-year-old Illinois native told Insider she relied on a high-protein diet and compression boots to get her through her matches.

Here's what the diet and wellness routine looks like for a US Open athlete.

Eggs, toast, and chicken on match days

On the day of a midday match, Keys fuels up with a hearty breakfast and lunch beforehand.

For breakfast, she has eggs on toast, with avocado, and sometimes a side of potatoes. For lunch, it'll be chicken with pasta or rice. After the match, she will load up on more carbs and protein to aid her recovery.

Keys, who has a brand partnership with the supplement maker Thorne, also has a chocolate whey protein shake to aid muscle recovery between strenuous matches against the best in the world of tennis. She drinks at least one protein shake every day during the off season.

She has a simple wellness routine, consisting of certain supplements and compression boots

The wellness industry is ballooning into a trillion-dollar behemoth, and athletes — who are professionally bound to staying in perfect health — are key to that growth.

These days, most professional athletes have some tie to a wellness product, from the lowest ranking to the super stars. LeBron James spends over a million dollars on biotechnology like cryogenic and hyperbaric chambers. Tom Brady sells infrared pajamas. Aaron Rodgers has touted the benefits of "cleanses" with roots in ancient medical systems (which experts say he performed incorrectly).

Keys has partnered with Thorne, though she says she keeps her wellness routine simple, taking supplements like omega-3, iron, the antioxidant glutathione and turmeric. Keys also takes vitamin D due to a doctor-diagnosed deficiency.

For most non-athletes, eating a balanced diet is the best way to get the right amount of nutrients, nutrition experts told Insider — though people with diagnosed deficiencies could benefit from using supplements.

For athletes, it may be slightly different (though research is lacking). Writing in the British Journal of Medicine, the International Olympic Committee — the best source of guidelines for top-tier athletes — recommends high-performance athletes work with an informed sports nutritionist to determine which supplements could benefit their bodies.

The supplement industry is also unregulated, meaning supplement makers do not have to test for efficacy, though (Thorne's products are certified with the National Science Foundation.)

Keys will increase her calories in the off-season as she prepares to compete next year

The US Open has ended, but professional tennis players like Keys tend to compete until November. Tennis has one of the shortest off-seasons among professional sports, with US competitions beginning in the spring.

Off seasons last between September to February if athletes only compete in US tournaments, but international competitions take place in every month except December, according to the Association of Tennis Professionals.

Keys said she typically has to eat more because her training is a more intense for those six to eight weeks. She adds an extra protein shake to her diet and increases her calories while eating primarily the same foods.

Keys said she does not watch what she eat or measures her calories — she would never be on a "super strict, crazy diet."

"I think a lot of times people think that athletes are constantly concerned about their weight and how they look, and it has so much more to do with fueling my muscles with the nutrients that they need to be strong and recover and be able to fuel me for the physical activity that I'm going out and doing every day," she said.