Kathy Cooper, 47, says she's never felt better than she does now. She has more energy and sleeps better since she went on the so-called caveman diet, she says.
It's a regimen that restricts followers to a basic diet of meat, fish, fruits and vegetables while eliminating all grains, beans, salt, sugar and dairy.
"I didn't do it to lose weight," she says. "When I switched over to Paleo (another name for the caveman diet), I felt so much better."
Christina Chew has also joined what's called the Paleolithic Movement. She started nine months ago and at first found the change daunting. Now she's convinced it helps her feel better.
"I have an even level of energy throughout the entire day. I no longer drink coffee at 3 o'clock in the afternoon. My moods are great, I no longer have PMS," she says. "The health benefits go on and on."
The diet has gained popularity among people who do a strength training program called crossFit.
But while its followers are devout, nutritionists say the strict diet is unhealthy.
"I would see the risk for long term to people not getting enough carbohydrates, which could disrupt their focus and concentration," says nutritionist Rebecca Scritchfield. "It could leave someone feeling cranky and irritable."
Critics also say restricting entire food groups makes the caveman diet extremely difficult to follow.