The diet includes foods our ancestors could have hunted or gathered, such as lean meat, fish, eggs, vegetables, fruits and nuts. It prohibits things not available to them, such as dairy products, grains, salt and sugar.
The rationale is that human beings aren't genetically designed to eat much of what we put into our bodies today. Nature intended us to follow a prehistoric diet, the theory goes, and our failure to do so has led to the epidemics of obesity, heart disease, diabetes and other chronic conditions.
As evidence, proponents cite the experiences of societies that have stuck closely to this dietary ideal. One is the tropical island of Kitava, part of Papua New Guinea, where studies show that modern maladies are rare. However, it's impossible to know for certain whether this is due to the Kitavans' diet or some other aspect of their lifestyle.
Several small, short-term studies have measured the effects of a Caveman Diet in Western populations. In one, nine overweight subjects who were put on the diet for 10 days experienced improvements in blood pressure, cholesterol, and glucose tolerance (a measure of how well the body handles sugar). In others involving people with diabetes or prediabetes, a Caveman Diet resulted in better glucose tolerance than a Mediterranean diet and more favorable readings for blood pressure, good cholesterol, and weight than a standard diabetes diet.
Though the research is too preliminary to permit any firm conclusions, it does appear that the diet's embrace of fruits, veggies and nuts, along with its avoidance of sweets, refined grains and junk food, makes it healthful overall. But there's little evidence that shunning whole grains, beans or dairy is necessary for optimal health.
Nor is there proof that eating lots of meat, as many of the diet's adherents do, is beneficial, and it could be harmful. The wild beasts that cavemen killed and consumed are a far cry from what we get at the supermarket -- even if it's organic, free-range and grass-fed.
In truth, we can't be sure what cavemen ate, which is a problem with the whole concept. Based on what anthropologists do know, prehistoric diets varied widely depending on where people lived and what was available to them.
Until there's stronger evidence, you may be better off leaving this diet in the history books.