Should You Eat Like a Caveman?


Carbohydrate restriction in The Zone Diet and the Paleo Diet actually hurt endurance sports performance.

In the new edition of Racing Weight just released this December, author and certified sports nutritionist Matt Fitzgerald debunks two popular diets among athletes, the Zone Diet and the Paleo Diet. Both diets are low-carb diets, restricting calories from carbohydrates, a fuel source that dozens of studies over decades have shown to be the most critical fuel source for high performing endurance athletes. Citing a wide variety of recent academic studies that show decreases in performance among devotees of the Zone and Paleo Diets, Fitzgerald argues that among endurance athletes, carbohydrate is king.

From the new edition of Racing Weight:

Such diets typically do not deprive athletes of the total calories they need to support their training. But like the popular weight-loss diets, they do tend to deprive athletes of adequate carbohydrate. Also, their restrictive, imbalanced nature makes them just as hard to sustain as low-calorie diets. Research dating back almost a century has demonstrated that lowcarb diets such as the Zone Diet reduce the body’s capacity to handle higher training loads. In 2002, researchers at Kingston University in England looked at the effect of the Zone Diet on training capacity in runners (Jarvis et al. 2002). Volunteers were required to run as long as they could at a fixed intensity of 80 percent of VO2max on two separate occasions: before starting the Zone Diet and again after a week on the Zone Diet. The average time to exhaustion before the Zone Diet was 37:41. A week later the average time to exhaustion had dropped all the way downto 34:06. Just seven days of inadequate carb intake had reduced these runners’ intensive endurance by nearly 10 percent.

Fitzgerald offers a few other critiques of the Paleo Diet in this recent post on

Racing Weight is a proven weight-management program designed specifically for endurance athletes. Revealing the latest research and drawing from the best practices of elite athletes, coach and nutritionist Matt Fitzgerald lays out six easy steps to help cyclists, triathletes, and runners lose weight without harming their training.