Dr. Stephen Phinney, a physician and nutritional biochemist, said he would advise Elon Musk to send people to Mars on a keto diet.

The high-fat, low-carb plan, Phinney said, costs "a heck of a lot less" when used in endurance feats because it allows people to carry fuel in their bodies in the form of fat rather than in their backpacks, bikes, or theoretical spaceships.

The diet is counterintuitive for endurance athletes who have long been known to need quick fuel in the form of carbohydrates.

But Phinney gave examples of elite endurance athletes who broke records on keto, and shared research showing that the eating plan may at least not be any worse for sports performance than a traditional higher-carb plan.

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Before Elon Musk sends people to Mars, he might want to consult Dr. Stephen Phinney about what the space explorers should eat.

Phinney, a nutritional biochemist and chief medical officer of diabetes-reversal company Virta Health, has been studying nutrition, and particularly ketosis, for decades.

He's learned that it may be easier for some people to excel in extreme endurance pursuits if they carry lots of fuel in their bodies, as the keto diet allows, rather than on their backs, bikes — or in their spaceships.

"It's going to cost a heck of a lot less to send people [to Mars] on a ketogenic diet," Phinney said at the Academy of Nutrition and Dietetics' annual Food and Nutrition Conference on Sunday in Philadelphia.

The keto diet is controversial for endurance athletes who've long been told to fuel with carbs

The keto diet is a low-carb, high-fat eating pattern that forces the body to burn fat, rather than carbs, for fuel.

While the plan is controversial in the nutrition community, it's especially counterintuitive for endurance athletes, who have long been known to need quick energy in the form of carbohydrates.

Phinney cited several examples of elite endurance athletes who broke records after going keto, suggesting that part of the diet's power for them was the ability to stop carrying carbs in the form of bagels, bananas, and goos.

Space travelers could potentially benefit from this as well, he said.

Back in 2012, ultra-endurance runner Tim Olsen won a 100-mile race, taking 21 minutes off the previous course record. He switched to a keto diet in order to avoid the digestive distress he'd previously experienced consuming the necessary 6,000 calories in carbs on the course, Phinney said.

Olsen won again the next year.

Then there's Mike Morton, who set a record running the most miles (172.5) over the course of 24 hours, as well as Sami Inkinen and Meredith Loring, the couple who made history rowing from California to Hawaii in 45 days. All were "keto-adapted," meaning their bodies had learned to use fat for fuel.

Endurance athletes have long been told they need plenty of carbs to succeed. iStock

Some research shows keto may not hurt endurance performance

Phinney also discussed research suggesting that the keto diet is at least no worse than a higher-carb eating plan for some endurance athletes.

In one of his studies, he and colleagues compared 10 elite ultra-endurance male runners who were eating a traditional high-carb diet to 10 other (physically similar) elite ultra-endurance male runners who were eating a low-carb diet.

Over the course of six months, the researchers found that the low-carb athletes used mostly fat as fuel while the higher-carb group's bodies used mostly carbohydrates.

Surprisingly, there was little difference in the two group's "resting muscle glycogen or depletion" during and after a three-hour run, meaning somehow the low-carb group's muscles were still able to store and replenish sugars without actually eating much sugar.

The results suggests athletes who are given long enough — in this case, six months — to get their bodies well-adapted to fueling with fat may be able to make what they need for fuel.

There's a healthy and unhealthy version of every eating plan. Shutterstock

High-quality human studies on keto are few and far between

Phinney and his fellow presenter Louise Burke, a sports dietitian who had a more cautious view of keto, said there's much more work to be done to understand exactly if, how, and why a keto diet can work for some endurance athletes, and to better understand why some people excel on it while others lag.

The overall takeaway is that "any diet can be followed in good and bad forms," Burke said.

Keto with plenty of vegetables and healthy fats is good. "Dirty keto" or "lazy keto" with a menu packed with "fat bombs" is bad.

"You've got to do it the right way if you're going to do it," she said.

Phinney isn't the only researcher to ponder the usefulness of keto in space. In 2017, a researcher tested the keto diet while participating in an undersea NASA experiment designed to simulate Mars living. His theory was that the diet could one day help protect people from the neurological risks of traveling in space.