To call Mark Sisson "ripped" doesn't even begin to capture the extent of how toned and in shape the 59-year-old is. While most of his cohort grapples with the side effects of obesity -- 30.8 percent of middle-aged people ages 45 to 64 are obese, the highest rate in the nation -- the former Ironman appears to be the very picture of health.
What does Sisson credit for his rock-hard physique? Cutting gluten -- the storage protein found in grains -- out from his diet entirely. Gluten-free is the way to be, he said.
"Gluten is poison!" Sisson told a reporter on NBC's "Rock Center."
Sisson instead favors what is known as the Paleo Diet: Eating "mostly fruits, vegetables, meats, nothing processed" like our caveman ancestors. Sisson said the effects to his health were huge.
"The arthritis that I had in my fingers that I thought was just a normal artifact of my 40s went away," Sisson said, before ticking off a number of other health benefits of a gluten-free diet.
Sisson's physique also comes from frequent exercise, he explains on his website. "I follow a routine that includes a workout five to six days a week for about 30 minutes," he writes. "Some of my workouts are as short as 10 minutes."
Maintaining a gluten-free diet has gained in popularity, with celebrities like Lady Gaga going gluten-free as a way to lose weight. However it's more than a fad diet for the 1 in 16 Americans (that's 18 million people) with a gluten sensitivity.