The basic idea is to eat like the cavemen did. That includes includes lean meats and fish, fresh vegetables, some fruit, nuts and seeds and good healthy fats.
I caught up with one woman who says she is hooked on the plan.
Inside the new R5 CrossFit gym in Wayne, it's all about strength, speed and getting fit.
And it doesn't stop with the grueling workout. Many CrossFit fans also follow the Paleo plan.
Jill Lotz started the diet last October as part of a challenge.
"It was a month-long challenge, but then I really kind of embraced it," she said.
And it worked. Photos show what she looked like before and after starting CrossFit and Paleo.
She tells me she lost 10 pounds in about seven weeks.
Plus, "my skin kind of cleared up, my mood improved, and it was all these things just from eating really good-for-you food, just natural food," she said.
The natural food is what Christine Ballantine, a holistic health coach, likes about the Paleo plan.
"There's no processed food," she said. "Getting away from processed food is great. So it is a nice clean diet from that aspect."
Another plus is that it typically gets people cooking, so you have more control over your food than eating out.
And it helps remind us to pay attention to our diet.
"As soon as you start looking at what you are eating you are going to do better," said Ballantine.
But she says some of the minuses of the Paleo diet are that it can be expensive and may be too restrictive for some people.
It cuts out cereal grains, legumes, all dairy and refined sugar.
Jill now follows Paleo about 80 percent of the time.
She recommends if you start, start slowly, cut out one thing at a time and add in something healthy.
"I've seen the improvement in myself, but I have also seen it in other people," she said.