The 5 Biggest Fat Myths

Your nutrition is just as important as your training. Don’t take bad advice on how to perfect it.

Fat has a complicated past. It went from being viewed as the fast track to weight gain to a surefire way for endurance athletes to teach their body to burn slower for longer. We looked at some of the most common misconceptions ideas behind the macronutrient—one of three nutritional components (fat, protein, and carbohydrates) required by humans to function—and stacked them up against the latest peer-reviewed literature and advice from the experts. Here’s what we found.

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MYTH: Cut fat from your diet to lose weight during training.

REALITY: For starters, you probably shouldn’t be trying to lose weight during training. If you have a few pounds to lose, do it ahead of time so you can fuel your body with enough calories to function and perform during intense training blocks.

Even when weight loss isn’t on the mind, “many athletes incorrectly believe that a low-fat diet is good for them,” says Bill Campbell, an exercise physiologist at the University of South Florida. That assumption is misguided. Not having enough fat in your body suppresses normal testosterone production in males, which can have negative implications for performance, he says. The U.S. Olympic Committee’s Weight Loss Fact Sheet, created specifically for athletes looking to lean out, recommends adding, not removing, fatty foods like nuts, seeds, and avocados to keep you satisfied for longer and to give your body fuel it can actually burn.

In your hardest periods of work, you shouldn’t skimp on the fats; rather, you should load up on them to power your efforts. “In a very heavy training phase, the required fat intake might be double the amount of the rest and recovery phase,” says Trent Stellingwerff, director of performance solutions at Canadian Sport Institute Pacific. 

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THE MYTH: High-fat diets help endurance athletes go harder for longer periods of time.

THE REALITY: Ketogenic diets are having a moment. Adherents swear by a life of foods like sardines, macadamia nuts, and fatty fish, saying the diet key to their endurance performance. But their views aren’t without controversy. Many scientists in the field take a more cautious stance. Louise Mary Burke, head of nutrition at the Australian Institute of Sport, has focused much of her research on how high-fat diets affect endurance athletes and recently called for a reexamination of the trend’s popularity and legitimacy, suggesting the scientific and endurance community claimed to have found the secret to high-mileage invincibility all too soon.

Part of the trouble in assuming high-fat diets work for everyone, researchers say, is in the difference between effort intensity across different types of sports, such as a marathon versus an ultra-distance race. With successful fat loading, athletes can store enough fat-derived energy—and still be lean—to power them through 50- and 100-mile races easily, says Stellingwerff. But it’s important to have at least some carbs to fuel a shorter race at a higher intensity or even to pick up the pace during the last ten miles of an ultra or tackle an exceptionally difficult stretch of the course. For a marathon distance or shorter, or any other endeavor where you’re more likely to be pushing the top of your aerobic capacity, it’s important to incorporate quickly digested, easy-access carbs like the classic gel mid-race or even a responsible carbo load a few days before the race.

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THE MYTH: Medium-chain triglycerides (MCT), best known for their presence in coconut oil, break down like carbohydrates, so you can eat them as an easy-to-digest energy source prior to exercise rather than traditional carbs.

THE REALITY: “On paper, it would seem as though MCTs ingested prior to endurance exercise would be beneficial for performance,” says Campbell. All fat molecules are composed of long strands of fatty acids, some longer than others. MCTs are composed of fewer of these fatty acids, so their chains are shorter, allowing the body to break down the molecules much faster and absorb them as energy.

“However, nearly all of the research that exists on MCTs suggests that it does not improve endurance performance,” says Campbell. Recent research found that cyclists who used MCTs had worse sprint performance and reported gastrointestinal upset during intense exercise. In short: Keep it simple and stick to carbs before your workouts.

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THE MYTH: A daily pill of L-carnitine, an amino acid derivative, keeps the fat away.

THE REALITY: Sold as miracle fat burners, L-carnitine supplements have been hailed by some as the best way to fast-track fat loss and get lean. But research on the pills paints a less compelling picture. Your body makes this compound on its own to move fatty acids to the mitochondria—the part of the cell responsible for energy production—where they’re metabolized. “The evidence of L-carnitine increasing fat oxidation and weight loss is tenuous at best,” says Stellingwerff.

Pro cycling teams have been known to use L-carnitine on a rigorous supplementation schedule of twice-daily intake with high-carb meals for up to six months, but their diet is dialed in such a way that the supplement helps to make them leaner, says Stellingwerff. In other words, they eat so little fat that there’s hardly anything left to burn, and the supplement burns through what little remains. If you’re following a standard healthy diet, however, the pills won’t make a difference.

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THE MYTH: All fats fall into the same macronutrient bucket, so I can eat any type—handfuls of almonds or slabs of ribeye—as long as I hit the right ratio of fat-to-protein-to-carb by day’s end.

THE REALITY: A recent and exhaustive study looked at more than 130,000 people in 18 countries and determined that those who had greater fat intake were more likely to live longer. But the perennial debate about which type of fat to eat rages on. Stellingwerff recommends that athletes avoid trans fats, like fried foods, desserts, and even crackers, and shoot for monounsaturated and polyunsaturated fats, which come in plenty of vegetarian- and vegan-friendly sources like olive oil and avocados. “I recommend athletes ingest one-third of their fat from monounsaturated sources like olive oil and nut butter, one-third from polyunsaturated sources like walnuts and fatty fish, and one-third from saturated fats like dairy products and red meat,” says Campbell.