On the days Evan Dunfee hasn't ingested enough fat, he'll melt butter in the microwave and then toss it back like tequila.

You'd think fat and Olympic-level performance would be mutually exclusive.

But the 26-year-old Dunfee, who became one of the feel-good stories of the Rio Olympics when he gracefully declined an opportunity to appeal his fourth-place finish in the 50-kilometre race walk, is part of a groundbreaking study at the Australian Institute of Sport on the effects of a low-carbohydrate, high-fat diet on endurance events.

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"You just get used to eating packets of butter," Dunfee said of the diet. "It kind of becomes part of what we do to keep our fat intake up. During 40K long (training) walks, we will eat cheese and peanut butter cookies. So it's radically different to anything any of us are used to. I don't think anyone would ever recommend eating cheese when you're three hours into a training session."

Dunfee will come off the diet Friday after a challenging three weeks. Barely a few days in, the six-foot-one athlete had already dropped almost nine pounds, plummeting to the lightest he'd been since he was 15 years old. He tweeted a picture of the scale reading 63.90 kilograms (141 pounds).

To rectify the weight loss, he consumed a glass of whipping cream, documenting it on Twitter with photo of him holding up the full cup and a stray bit of cream stuck in his red beard.

On Australia Day last Thursday, Dunfee was allowed a treat: an Atkins bar with two grams of carbs.

The science behind the diet, simply put, is that strictly limiting carbohydrates forces the body into ketosis, a state where fat is burned as a fuel rather than carbohydrates. Even a slender athlete like Dunfee carries enough fat stores to fuel days of exercise, he explained, while glucose is limited and has to be replenished during exercise.

Dunfee participated in Part 1 of the study last year, the results of which were recently published, and 10 days after coming off of the low-carb diet he obliterated the Canadian record in the 50 kilometres by over four minutes.

The Richmond, B.C., native said he isn't entirely sure exactly what propelled him to the record. It might have been the diet and the physiological adaptations his body had made from being on it. Or perhaps it was more a mental toughness gained while training on such a strict diet. Or maybe it was just the fact he'd spent several weeks in Australia training with some of the world's best walkers.

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"That race almost felt easy," Dunfee said. "So that really piqued my interest of saying 'OK, maybe there's something here."'

Countless top athletes certainly believe there's something there. Cleveland Cavaliers star LeBron James famously dropped a large amount of weight (he never specified how much) in 2014 by following a ketogenic diet for 67 days. British cyclist Chris Froome credited a low-carb diet with propelling him to three Tour de France titles. The Australian cricket team had a turnaround in form after collectively slimming down on a low-carb diet.

Canadian javelin thrower Liz Gleadle talks fondly about grass-fed butter like some of us would chocolate cake.

"Who's ever dissatisfied with eating something that's been covered in grass-fed butter and garlic and olive oil and salt? It's never not a tasty option," Gleadle said. "You really learn a lot about your choice of quality of foods, you're looking for really high-quality fats, and when you have them you don't feel bad about them, which is a really nice feeling."

The 28-year-old Vancouver native started cutting down on carbs last year to combat the lethargy she was experiencing between practices. After some experimentation and plenty of research — "The Big Fat Surprise" and "Primal Blueprint" were at the top of her reading list. She's reduced the amount of carbs she consumes during the week when training. On weekends, which she takes a break from training, she'll eat an exceptionally low-carb diet or even fast for 16 hours.

The results?

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"Big things I noticed were unbelievable mental clarity. I went from having to nap or watch TV because I could barely focus on a book, to all I do now all day between practices is read and research," said Gleadle, who won gold at the 2015 Pan Am Games in Toronto. "My skin got infinitely healthier. It was really noticeable, I was getting tons of compliments from people 'You look great, what have you done?'

Gleadle said she also notices that her joints don't hurt in the morning.

A quick social media search of the hashtags "keto" or "LCHF" suggests that a low-carb, high-fat movement that is growing among the general public.

Trent Stellingwerff, an applied sport physiologist who works with many of Canada's top athletes, cautions that high-performance athletes have different dietary needs than the average person.

"There is a whole huge burgeoning underground of average people who are being more conscious of how much carbohydrates they have in their diet," he said. "But this diet for health and weight outcomes is totally different and separate than looking at this from a performance perspective. And sometimes those lines get blurred."

According to the Canada Food Guide, 45 to 65 per cent of our diet should come from carbohydrates, or between 210 and 290 grams per day as part of an average 1,800-calorie diet.

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Gleadle consumes between 70 and 130 grams a day during the week. Dunfee has consumed about 40 grams a day as part of Australian Louise Burke's study.

Dunfee and Mat Bilodeau of Calgary are among 28 race walkers from around the world taking part in the study. After the diet ends Friday, athletes will be tested and monitored for several weeks. Dunfee compared the rigorous practice to altitude training, and its adaptations the body makes to training with less oxygen.

"Altitude is a perfect analogy," Dunfee said. "And when you come back off the diet, you have adaptations that are advantageous to perform better under ideal conditions with carbs. So that's the idea, and it could be quite game-changing in terms of sports nutrition guidelines, and what's recommended."

Dunfee became one of Canada's most popular athletes at the Rio Olympics when he finished fourth after being jostled and thrown off his stride by Hirooki Arai. The Japanese walker was disqualified but then reinstated after an appeal. Dunfee chose not to launch a counter-appeal.