In the days before winning the women’s halfpipe gold medal at the 2018 Winter Olympic Games, American snowboarder Chloe Kim was tweeting about ... food. Ice cream and churros, to be exact.

Could be down for some ice cream rn — Chloe Kim (@chloekimsnow) February 12, 2018

Oh and I also had 2 churros today and they were pretty bomb so if you ever get nervous go eat a churro — Chloe Kim (@chloekimsnow) February 11, 2018

With every Olympic Games come tales of athletes’ favorite junk foods: the ice cream, Chinese food, and burgers they reportedly indulge in to relieve some of the stress of training. The implication is that with all the exercise these athletes do, they can eat whatever they want.

While it may be true that Olympians sometimes cut loose, their diets tend to be remarkably junk food-free — and highly optimized for performance.

Athletes are looking for any edge. Increasingly, that means practicing extreme caution about what foods they use as fuel. “These events are won by less than 1 percent — the margin of victory is really quite tiny,” Mayo Clinic exercise researcher Michael Joyner said.

To learn more about the sophisticated — and sometimes mysterious — eating practices of Olympians, we talked to the dietitians and nutritionists who work with them. We learned that the art of feeding athletes has become extraordinarily fine-tuned, calibrated daily to their workouts and competitions. We also learned that, far from ice cream and burgers, athletes these days eat clean.

Athletes need to calibrate their calories to meet the demands of their sport

Feeding elite athletes these days is a full-time job. For years ahead of the Winter Games, four sports dietitians have been working with Team USA, drawing up nutrition plans, educating them about food, cooking with them, even helping them grow their own food.

The work continues in South Korea: Team USA shipped to South Korea 85 pallets’ worth of food and equipment — weighing hundreds of pounds — so athletes had exactly what they needed for fuel at all times.

A big challenge for sports nutritionists who work with athletes is making sure they have enough energy to compete in their particular event. Different sports have vastly different energy needs — and most athletes don’t eat anywhere near as much you might think.

To calibrate the correct number of calories, sports nutritionists need to calculate how hard the athletes are training, how much energy they are likely to burn, and how heavy or light they need to be for competition.

Ski jumpers, for example, are at the very low end of the spectrum, eating as little as 1,300 calories per day.

“They come from a large height, come down, and fly as far as they can, so they have to weigh extremely light. The lighter you are, you fly farther,” said Susie Parker Simmons, one of two senior sports nutritionists with the United States Olympic Committee.

These men and women typically weigh up to 10 or more pounds less in the days before competition compared to their typical bodyweight, so that means restricting their calories to eat even less than their bodies might burn. Ditto for figure skaters, who need to ensure they’re light and agile enough to jump and glide across the ice.

Parker Simmons photographed the typical dinner of a female ski jumper: It involved only one and a half cups of vegetables, 3 ounces of meat, and half a cup of grains.

On the other end of the energy-need spectrum are the cross-country skiers. The have the highest energy expenditure of any sport — even higher than running and cycling — because they use their lower and upper body strength to push through snowy terrain. Men on average might eat 7,000 calories per day, and women 5,000.

So, Parker-Simmons said, a dinner for a female cross-country skier might involve a bun or roll with 4 ounces of meat, a cup of vegetables, a cup of quinoa, and a cup of baked potato wedges, as well as yogurt and fruit (not shown).

You see a little caloric variation between athletes at breakfast time too. In a Bon Appétit feature by Alyse Whitney about Olympic athletes, Team USA cross-country skier Jessie Diggins said he loads up on a cup of dried oatmeal, a cup of berries, yogurt with nuts and honey, and a fried egg, or French toast or pancakes topped with peanut butter, bananas, and nuts. Figure skater Adam Rippon, on the other hand, eats only oats and almond milk for breakfast.

Athletes’ diets are always changing — but they are consistently clean

It’s not just how many calories athletes consume; they also need to consider what type of calories they need. If they are doing the kind of strength training that builds muscle, like weightlifting, they’ll need to ramp up their protein intake. If they are doing lots of cardiovascular work, like during cross-country skiing, they’ll need lots of carbs so their body has enough fuel ready to burn.

“A longer endurance event, such as [the] cross-country skiing 50-kilometer event, athletes will carbohydrate load to maximize the glycogen and energy stores leading into their event,” explained Joanna Irvine, a dietitian with the Canadian Sport Institute Pacific who works with athletes on Team Canada.

For bobsleigh and luge, the demands of the event are much different where their starts are critical to performance. “A luge or bobsleigh athlete will look to be reactive and quick off the start line and wouldn’t require the high carbohydrate intake,” Irvine said.

Depending on how close athletes are to their competition, their nutrition goals and objectives will also shift.

Just before a longer high-intensity training event, athletes will need to eat extra carbs to power through the game — but for a workout that may be more technical, or on days off, Irvine said, they’ll eat fewer calories and carbs. On those days, “an athlete may focus on a vegetable- and nutrient-rich meal, decreasing carbohydrates to match the demand and spacing out the protein throughout the day.”

No matter the day, all athletes now have something in common: They eat remarkably clean diets.

As we learned during the 2016 Summer Olympics in Rio, athletes are generally meticulous eaters — more like Gwyneth Paltrow than Michael Phelps (whose legendary training diet involved 12,000 calories of eggs, French toast, pizza, and pasta).

Instead, the summer athletes in Rio reported sucking back green smoothies and beet juice, along with salads or sandwiches. In the Bon Appétit feature about winter athletes’ breakfasts, athletes reported consuming mainly oatmeal, eggs, fruits, vegetables, salmon, and yogurt — all health foods by any measure.

This focus on clean eating is relatively new. “I have seen a very encouraging shift in buy-in from athletes,” Irvine said, “regarding how nutrition can impact their performance, uncovering and gaining those extra 1 percent advantages that may be the difference between a first- or fourth-place finish.” So winning these days, it seems, starts at the breakfast table.