Could Paleolithic man hold the key to today's nutrition problems?
A growing number of adherents to the so-called "caveman" diet contend that a return to the hunter-gatherer foods of the Stone Age -- heavy on meats, devoid of most grains -- could alleviate problems like obesity, type 2 diabetes and many coronary problems.
The Paleo diet movement is backed by some academics and fitness gurus, and has gained some praise in medical research in the US and elsewhere even though it goes against recommendations of most mainstream nutritionists and government guidelines.
Loren Cordain, a professor of health and exercise science at Colorado State University, said he believes millions in the United States and elsewhere are following the Paleo diet movement, based on sales of books such as his own and Internet trends.
"It was an obscure idea 10 years ago, and in the last two to three years it has become known worldwide," Cordain, one the leading academics backing the Paleo diet, told AFP.
"There are at least a half-dozen books on the best seller list that are promoting this," he added.
The underlying basis for the Stone Age diet is a belief that homo sapiens evolved into modern humans with a hunter-gatherer diet that promoted brain function and overall health. Backers say the human genome is essentially unchanged from the end of the Paleolithic era 10,000 years ago after evolving over millions of years.
"It's intuitive," Cordain said. "Obviously you can't feed meat to a horse, you can't feed hay to a cat. The reason for that is that their genes were shaped in different ecological niches."
He said peer-reviewed research has shown the Paleo diet better than the Mediterranean diet, US government recommendations and diets aimed at controlling adult diabetes.
One study published in the Journal of Diabetes Science and Technology showed a Paleolithic diet "improved glycemic control and several cardiovascular risk factors compared to a diabetes diet."
A Swedish study published in the Journal Nutrition and Metabolism found that a Stone Age diet is "more satiating per calorie than a Mediterranean-like diet," making it something to be considered in fighting obesity.
Some aspects of the Paleo diet are widely accepted, such as shunning many refined and processed starches and sugars in favor of fresh fruits, nuts and vegetables. But the controversy stems from its elimination of most cereals, legumes and dairy products, relying instead on high-protein meats, fish and eggs.
The Paleo diet has a devoted following, some who link it to improved fitness and longevity, including Arthur De Vany, a 74-year-old former economics professor who promotes vigorous workouts and wrote a 2010 book, "The New Evolution Diet: What Our Paleolithic Ancestors Can Teach Us about Weight Loss, Fitness, and Aging."
"Our forager ancestors sought out high-energy (meaning high-calorie, high-fat) foods that could be obtained at the lowest energy cost," De Vany says in his book.
"We began getting heavier and developing new diseases once we ceased to be hunter-gatherers and instead became farmers -- or more specifically once we started eating the food we grow rather than gathering food."
But a US News survey of nutritionists ranked the Paleo diet last among 20 possible options, far below the Mediterranean, vegan or Weight Watchers diets.
It noted that the Paleo diet gets 23 percent of calories from carbohydrates compared to 45 to 65 percent in US government recommendations, and that the Stone Age regime is higher than recommended for protein and fat.
"While its focus on veggies and lean meat is admirable, experts couldn't get past the fact that entire food groups, like dairy and grains, are excluded on Paleo diets," US News said.
Marion Nestle, professor of nutrition, food studies, and public health at New York University, told AFP that the Paleo diet "would not be appropriate for today's sedentary lifestyles."
Nestle and others also dispute some of the historical claims of Paleo diet advocates. "The claim that half the calories in the Paleolithic diet came from meat is difficult to confirm," she said.
In a research paper, Nestle said the life expectancy of Stone Age man was around 25 years "suggesting that the Paleolithic diet, among other life conditions, must have been considerably less than ideal."
Cordain argues however that there are modern societies of hunter-gatherers where the theory can be tested.
In these societies, "elderly people have been shown to be generally free of the signs and symptoms of chronic disease (obesity, high blood pressure, high cholesterol levels) that universally afflict the elderly in Western societies," he says on his blog.
"When these people adopt Western diets, their health declines and they begin to exhibit signs and symptoms of 'diseases of civilization.'"
Cordain acknowledges that because of the way society has evolved, it is impractical to feed the world with Paleo diets because many societies have become dependent on cereals.
But he says it can be successfully used in many Western countries, and argues that despite jokes about the Stone Age, mainstream nutritionists will come around to his conclusions.
"This is not a fad, this is not Fred Flintstone, this is the wave of the future," he said.
