The paleolithic diet, also known as the paleo diet, caveman diet, Stone Age diet or hunter-gatherer diet, was first popularized in the 1970s by gastroenterologist Walter L. Voegtlin, and has since been adapted by a number of others, including Loren Cordain. The diet plan puts the eater in their best Fred and Wilma mode, allowing them to dine on fresh meats, fish, seafood, fresh fruits, vegetables, seeds, nuts and healthful oils. Basically, if our ancestors ate it during the Paleolithic era, before the development of agriculture and grain-based diets, you can too. That means, no grains, legumes, dairy products, potatoes, refined salt, refined sugar and processed oils.
The idea is based on research that hunter-gatherers typically were free from the chronic illnesses and diseases that are epidemic in Western populations. Although on paper it seems pretty sensible, the latest U.S. News & World Report ranking of diets placed it near the bottom of the list, rating it low for weight loss, heart health and ease of use: "It’s one of the few diets that experts actually considered somewhat unsafe and only somewhat complete nutritionally."