Endurance athletes have long been told to carb-load for optimal athletic performance, but scientists now say high-fat, low-carb diets such as the ketogenic and Paleo diets may actually be better for marathon runners, cyclists and triathletes.
Two recent studies suggest a high-fat diet does not increase body-fat storage or boost the risk of heart disease, contradicting longstanding low-fat diet dogma that eating fat makes you fat and causes heart attacks.
One study tracked 12 long-distance runners over a period of eight weeks, while another study followed 28 triathletes over 15 weeks.
Study: Low-Fat Diet Reduced Good Cholesterol
Both studies showed that a high-fat diet had no effect on subjects' fitness levels or cardiovascular risk factors. However, the low-fat diet seemed to negate some of the positive effects of exercise in the endurance athletes, including lowering their HDL cholesterol (the good cholesterol) and increasing their heart-disease risk.
The results confirm what former Ironman triathlete Mark Sisson experienced himself. Sisson said he improved his athletic performance, his body composition, and his energy levels after switching to a low-carb, high-fat (LCHF) Paleo diet.
Sisson, author of The Primal Blueprint, used to carb-load during his years as an endurance athlete, but said he actually got healthier while doing less exercise after going Paleo.
“I fell into the paradigm of eating complex carbs for fuel,” Sisson told Palm Springs Life. “I got fit, but my health declined. I was one of the top runners in the country but had many health ailments.”
Mark said by reducing carb intake and increasing the amount of healthy fats, your body learns to burn fat (instead of glucose) for fuel.
"Over time, you become good at burning off your own body fat for energy rather than depending on carbohydrates throughout the day," said Sisson. "It takes about 21 days for your body to switch to this mode of fat-burning, and that’s when you’ll really start to see results.”
Ironman triathlete Nell Stephenson agrees. Stephenson switched to the high-fat, low-carb Paleo diet after contracting a parasite during an Ironman triathlon in 2004. After finding no relief with prescription drugs, Nell adopted the Paleo diet, which emphasizes high-quality animal proteins, healthy fats, vegetables, and excludes gluten, sugar, dairy, legumes, starches, alcohol and processed foods.
“I felt better in three days,” said Stephenson, author of Paleoista: Gain Energy, Get Lean, and Feel Fabulous. “My body is functioning optimally."
Ketogenic and Paleo Diets Boost Fat Oxidation, Curb Inflammation
Pro cyclist Dave Zabriskie, and ultra-marathoner Timothy Olson also abandoned their high-carb, low-fat eating plans in favor of the high-fat, lower-carb Paleo diet, and experienced meaningful performance gains.
Similarly, former Ironman triathlete Ben Greenfield trained for the 2013 Ironman Triathlon World Championships by following the LCHF ketogenic diet, and completed the epic endurance race in an impressive 9:59:26.
Greenfield previously followed a high-carb diet but switched two years ago after realizing that too many carbs causes inflammation, which can lead to heart disease, Alzheimer's, obesity, and diabetes.
"Two years ago, I came across research about pancreatic fatigue and failure, loss of insulin-cell receptor sensivity, and surges in blood glucose leading to inflammation," Greenfield said on a podcast with fitness expert Sam Feltham.
After switching to a ketogenic diet, Ben experienced improved stamina, stable blood sugar, better sleep, and less brain fog. Greenfield, author of Beyond Training, no longer follows the ketogenic diet, but advocates consuming plenty of healthy fats.
Joe Friel, a U.S. Olympic triathlon coach, said the Paleo diet (which is lower carb and higher fat than the traditional diets of endurance athletes) works for endurance athletes because it helps with recovery.
“[Paleo offers] better long-term recovery due to greater micronutrient content [than a standard high-starch, high-sugar diet], allowing the athlete to train with a greater stress load,” said Friel, author of the Triathlete's Training Bible.
Joel said the Paleo menu provides more antioxidants and vitamins than the typical high-carb diet favored by most endurance athletes and boosts fat oxidation and weight loss — a major advantage for endurance athletes, because the less excess weight you carry, the faster you'll be.