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.

Earlier on Huff/Post50:

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  • Exercise

    Exercising does more than improve your exterior. Several studies have found <a href="http://well.blogs.nytimes.com/2010/01/27/phys-ed-how-exercising-keeps-your-cells-young/" target="_hplink">an active lifestyle keeps your cells young</a>, according to <em>The New York Times.</em>

  • Eat Carrots, Pumpkin and Squash

    These orange veggies are chock full of the phytonutrient alpha-carotene, which <a href="http://www.latimes.com/health/boostershots/la-heb-alpha-carotene-112310,0,2855017.story" target="_hplink">lowered the risk of dying from cancer and cardiovascular diseases</a> in a study, according to <em>The Los Angeles Times</em>.

  • Avoid Too Much Sun

    Sun worshippers, take heed: Between <a href="http://www.who.int/uv/faq/skincancer/en/index1.html" target="_hplink">two and three million people are diagnosed with skin cancer</a> globally each year, according to the World Health Organization. With May being Skin Cancer Awareness Month, <a href="http://www.thirdage.com/skin/skin-cancer-awareness-month">Third Age has tips on how to avoid the "potentially fatal cancer."</a>

  • Have Sex

    A ring-a-ding-ding! Dr. Braverman of <em>The Doctors</em> suggests <a href="http://www.thedoctorstv.com/main/content/Anti_Aging" target="_hplink">having sex at least two times a week to help "reboot the brain</a>."

  • Take Your Omega-3s

    Studies suggest that foods rich in this fatty acid may reduce your risk of Alzheimer's.

  • The Computer-Exercise Combo

    <em>Huff/Post50</em> recently reported on a study that had subjects <a href="http://www.huffingtonpost.ca/2012/05/01/preventing-memory-loss_n_1465789.html?ref=fifty&ir=Fifty&just_reloaded=1">do moderate exercise and use a computer, which resulted in increased memory function</a>.

  • Up Your Glutathione Intake

    <a href="http://communities.washingtontimes.com/neighborhood/quality-life-concierge/2012/apr/16/glutathione-anti-aging-machine/">Glutathione is a rock-star antioxidant found in the body's cells</a> that "neutralizes harmful free radicals," and keeps cells running smoothly, <a href="http://www.webmd.com/food-recipes/features/glutathione-new-supplement-on-block" target="_hplink">according to WebMD</a>. To attain these benefits, eat a diet loaded with fruits and vegetables.

  • Own A Pet

    While there are conflicting reports on whether or not pets will add years to your life, it is confirmed that <a href="http://newoldage.blogs.nytimes.com/2012/03/30/rethinking-the-value-of-pets/" target="_hplink">pets can ease stress and lower blood pressure</a>, <em>The New York Times</em> reports.

  • Limit Sugar Intake

    A spoonful of sugar may make the medicine go down, but it also "<a href="http://www.ucsf.edu/news/2012/02/11437/societal-control-sugar-essential-ease-public-health-burden" target="_hplink">changes metabolism, raises blood pressure, critically alters the signaling of hormones and causes significant damage to the liver</a>," according to three doctors at the University of California at San Francisco. In a <a href="http://www.nature.com/nature/journal/v482/n7383/full/482027a.html" target="_hplink">recent issue of Nature</a>, they argued that the health hazards of sugar are similar to those related to drinking too much alcohol.