The Paleolithic diet has gained substantial ground in the past two years as more nutritionists and health gurus turn a skeptical eye to the benefits of a grain-based diet, which most Americans eat.

Embracing the foods of hunter-gatherers, the Paleo diet is red-hot right now. Celebrities such as Matthew McConaughey, Jessica Biel and Miley Cyrus are reportedly eating like cavemen.

But the Paleo diet is hardly new. First popularized in the mid-1970s by gastroenterologist Walter Voegtlin, it in many ways resembles the South Beach, Atkins and other low-carb regimens. The Paleo diet consists of fish, grass-fed pasture-raised meats, vegetables, fruit, mushrooms, nuts and roots, while eschewing grains, legumes, potatoes, refined salt, refined sugar, processed oils and, in most cases, dairy products. The basic idea is that by adopting this pre-agricultural diet, people may circumnavigate some of the “diseases of civilization.”

For Wendy Schwartz, 49, of Safety Harbor, Fla., the Paleo diet was a New Year’s resolution two years ago. She has bachelor’s and master’s degrees in food and nutrition from New York University.

“I took a divergent path,” she said. “I got out of nutrition, but my passion has been studying nutrition and learning about supplements.”

Since adopting the Paleo diet, Schwartz has lost 25 pounds, but she perceives her health benefits to go far beyond weight lost.

She differentiates Paleo from other low-carb diets because, she says, Paleo focuses not only on what you eat but the source of your food. Paleo focuses on quality ingredients whenever possible and really restricts the use of grains.

Schwartz found Paleo because she was having trouble digesting wheat products. In the age of the gluten-free craze, the Paleo diet fits in nicely.

The Paleo diet has detractors. Some nutrition experts are concerned with increased consumption of saturated fat from the meat-centric diet and a lack of calcium from the elimination of dairy. Also, there is much research that shows legumes and whole grains help fight some diseases of aging and keep blood sugar at appropriate levels. Neither is part of the Paleo diet.

“There’s no real research behind it,” Lisa Sassoon, a registered dietitian and assistant clinical professor of nutrition at NYU, told the Huffington Post last year. “And it eliminates things that do have research behind them: grains, beans and low-fat dairy.”

Still, Schwartz is a staunch proponent and offers these suggestions for moving toward a Paleo diet:

•Eat real food. If you can buy food that doesn’t have labels, that’s ideal.

•If your great-grandfather didn’t eat it, don’t eat it. Stop buying foods that have long, complicated ingredient lists.

•As far as vegetables, focus on fresh lettuces and try to order vegetables without sauce (order olive oil on the side).

•Stop thinking that low-fat is the way to go. Incorporate more extra-virgin olive oil, coconut oil or avocado oil.

•Focus on vegetables and healthy oils, and, preferably, pastured and grass-fed lean meats.

•If you can buy grass-fed and pasture-raised meat, get higher-fat cuts. If you can’t, go with leaner cuts. (And don’t rely too heavily on meat: It should be no more than 35 percent of daily calories.)