What's up with ... Stone Age snacking?

When swimmer Amanda Beard wanted to get in shape after the birth of her son, she decided to go back the basics -- as in 2.5 million years back. The Olympic gold medalist decided to follow a Paleolithic, or Paleo, eating plan, which consists of only the foods that our hunter-gatherer ancestors subsisted on, too.

According to Paleo proponents such as radiologist Boyd Eaton, M.D., and exercise physiologist Loren Cordain, Ph.D., humans evolved to thrive on a diet of meat, fresh produce and nuts. More recent foods, like sugary treats, packaged goods and even grains ("invented" 10,000 years ago) are to blame for the spike in weight gain and chronic illness, they say, because the body doesn't digest these as effectively. Although the premise for this Flintstones-era diet has existed since the '70s, it's recently grown in popularity, particularly among athletes like Beard.

The nitty-gritty

While there are different interpretations of the diet, the basic tenet revolves around eating the whole, natural foods our predecessors consumed. Followers eat mainly lean meat, fish, nuts, fruits and vegetables; corn, wheat, sugar, dairy and most beans, as well as fried and packaged foods, are to be avoided. The result: You consume about 30 percent of your calories from protein, 30 percent from fats (mostly unsaturated) and 40 percent from carbohydrates (mainly from produce). By comparison, the typical athlete's diet consists of 60 percent of calories from carbs, 15 to 20 percent from protein, and the remainder from fat.

The real deal

"The diet consists of unprocessed and unrefined foods, which can improve nutrient intake," said sports nutritionist Ryan Andrews, M.S., R.D., the director of education at Precision Nutrition, a nutrition coaching company. But because the plan is so low in carbs, many endurance athletes, like runners, cyclists and triathletes, find it too difficult to stick with when they're training. The diet is better suited for sports that require muscle mass at a lighter weight, like diving, gymnastics and rowing.

"When I'm close to a competition, I'm super-strict Paleo," said Ursula Gropler, the current world record holder in the indoor ergometer, and one of the world's best lightweight rowers. "It helps me get the leanness I need to compete, while still supporting good eating habits." Other athletes say that the super-restrictive diet is too difficult to follow 24/7. "On Paleo, my body fat is lower, energy levels seem higher and my performance is better," said Becca Borawski, a top martial arts and Crossfit athlete [Crossfit mixes elements of gymnastics, track and field and bodybuilding]. "But because it's so restrictive, I do it five or six days of the week."

If you want to try Paleo, Andrews recommends starting with a modified plan. "Athletes with high calorie and carbohydrate requirements will need to include some starchy veggies, like potatoes, beans and possibly some whole grains to get the nutrients they need," Andrews said.