How do Olympians eat? Clean and, often, very little.

In 2008, Olympic swimming champion Michael Phelps shocked the world when he revealed the smorgasbord he fueled up on every day.

There were the three fried egg sandwiches "loaded with cheese, lettuce, tomatoes, fried onions and mayonnaise," according to the Wall Street Journal. Then came a five-egg omelet, grits, and heaping piles of greasy French toast and chocolate chip pancakes. For lunch and dinner, Phelps said he downed nearly two pounds (or two whole boxes) of pasta, plus sandwiches and pizza.

All told, Phelps was sucking in about 12,000 calories — around five times what's recommended for the average American man. (He recently told the Washington Post that these days he eats and trains much less than he did in 2008.)

Still, Phelps's former diet remains legendary, bolstering the stereotype of the carb-loading athlete who can get away with an anything-goes approach to food.

But the eating habits of athletes today look quite different. We asked sports nutritionists who work with elite athletes and researchers who study performance nutrition about how top athletes actually eat. We also looked at the training diets of current Team USA Olympians, zeroing in on how they fuel up at lunch.

We learned that when it comes to eating to win at this year's Olympic Games in Rio, many athletes are meticulous eaters. From green smoothies and beet juice to salads and sandwiches, not only are they eating really clean, but many don't eat much at all.

As winning gets harder, athletes have cleaned up their diets

In a survey of the training diets of Olympic athletes by SB Nation and Eater, the reporters found health foods like Greek yogurt, oatmeal, and kale were surprisingly prominent. There was nary a pizza or pancake in the mix during training season except for the odd celebratory meal.

When we looked at the lunches of six current Olympians, we found much the same. For example, US gymnast Gabby Douglas goes for grilled chicken breast and asparagus for her midday meal.

This turn to clean eating, sports nutritionists say, happened only very recently.

"There's been a change in the last few years where athletes have become more serious about thinking about what they're putting into their bodies," said Asker Jeukendrup, a leading sports nutritionist who has worked with Olympic champions and is currently a visiting professor at Loughborough University in the UK. "The differences between winning and not winning are becoming smaller and smaller, and more and more athletes are becoming serious about nutrition."

Sports nutritionist and trainer Matt Fitzgerald recently traveled to five countries to study the diets of elite athletes, with a particular focus on endurance sports, for a forthcoming book called The Endurance Diet.

"I did not see many of the Michael Phelps–style anything-goes diets," he said. "And that seems to be fairly recent evolution over the last two generations of athletes."

Among the 130-plus elite endurance athletes he surveyed, he noticed their eating patterns were balanced and clean. "Although they eat everything, they skew toward the highest-quality food types — natural and unprocessed," Fitzgerald said. The athletes also didn't follow popular fads, like avoiding gluten, or restrict themselves from eating particular foods or food groups. They even indulged in the occasional sweet or drink — though that happened at the margins.

Julie Johnston, a member of the US women's soccer team competing in the 2016 Rio Olympics, concurred. "I've tried to focus on fresh fruits and vegetables to fuel my body … with the right things," she said. Instead of obsessing about calories, she added, "I just make sure what I'm eating is nutritious." Her typical training lunch is a modest smoothie and chicken soup.

Johnston's lunch pick mirrored that of trap shooting champ Corey Cogdell-Unrein, who favors a simple mix of chicken and vegetables for lunch.

There's a massive variation in the number of calories required among different types of athletes

Beyond making sure their food picks are healthy, athletes need to consider how to fit enough nutrients into diets with varying energy requirements. Different types of sports have vastly different energy needs — and most don't eat anywhere near what Phelps was consuming in 2008, according to Nanna Meyer, an assistant professor of health sciences and sport nutrition at the University of Colorado in Colorado Springs.

At the low end of the energy expenditure spectrum are the aesthetic (i.e., gymnastics) and weight-class (judo, wrestling) athletes. They may use less energy during their workouts or competitions, and have to stay within a certain weight category in order to compete.

The weight-class athletes in particular "will go to an extremely low intake and do all sorts of things to lose bodyweight in the days before they compete," such as using dehydration techniques like working out in saunas to quickly lose water weight, said Jeukendrup.

Team USA wrestler Jordan Burroughs's go-to lunch, for example, is a fresh-squeezed juice with ginger, turmeric, kale, and beets — a choice that may sound more like the meal of a detox dieter than a hard-training Olympian. (You can learn more about why exercise actually burns fewer calories than you might imagine in our previous piece.)

Among these athletes, getting a balanced diet becomes a particular challenge. "You're trying to get all the nutrients into very small meals," Jeukendrup added. "If you can only eat 1,200 calories, that can be really problematic."

At the other end of the calorie spectrum are the endurance athletes — the swimmers, runners, rowers, and marathoners. These sports require a lot of readily available energy, which typically comes in the form of carbohydrates.

"Some of our Olympic rowers will consume 8,000 to 10,000 calories per day, but many of them are over 6 feet, 5 inches and 220 pounds and train between 20 and 30 hours per week," said sport physiologist and nutritionist Trent Stellingwerff of the Canadian Sport Institute. 

Here's Team USA swimmer Nathan Adrian on his typical lunch: "I'll eat a fairly large sandwich — turkey and provolone with lettuce, tomato, and banana peppers is my go-to," he told Cosmopolitan; he follows that with a Korean rice bowl, frozen dumplings, and fruits and veggies. While it's not a Phelps-style junk food gorge, Adrian is consuming a lot of calories to fuel his swimming routine.

Strength and power athletes — who do sports like shot put or weightlifting — typically require fewer calories but more protein to build their muscles.

US Olympic weightlifter Morghan King makes sure her every meal is high in protein, via eggs and meat. For her, lunch is a stir-fry of lean meat, with some rice and vegetables. As King told Elle, she enjoys "cheat food" like pizza — but only in moderation. "I am very strict with my diet, but it's not some crazy diet," she added. Instead, she says she focuses on "eating real foods." Definitely more Michael Pollan than Michael Phelps.

With files from SB Nation's Ryan Connors, Julia Lee, and Ali Sidiki.