Many modern-day diets look to prepared low-fat, high protein or low-calorie options as the ideal way to lose weight, but what if you could lose weight without any of these strategies? Instead of buying packaged “diet” foods, people would go outside and fetch dinner for themselves, like hunters and gatherers of the Stone Age did to survive.

William R. Leonard, anthropology chair of the Weinberg College of Arts and Sciences at Northwestern University, said reverting back to a Paleolithic diet could be the answer to our country’s health problems.

After studying biology at Penn State University and earning his Ph.D. in biological anthropology from the University of Michigan, Leonard has spent his career studying human evolution and ecology. He talks about Paleolithic diets and the Discovery Channel’s “I Caveman,” a show he helped orchestrate along with doctoral candidate Aaron A. Miller that features 10 people who lived on a diet of meats, fish, fruits, vegetables roots and nuts in Colorado.

Q. Tell us about your research. What drew you to studying Paleolithic diets?

A. My research examines how human populations, in the past and today, adapt to the particular stressors of their environments, and how these adaptations influence their biology and health. Much of my work particularly focuses nutritional and metabolic adaptations: how do populations adjust to constraints or abundance in food availability, and what are the implications for various aspects of health and wellbeing (for example, child growth, obesity, or malnutrition, chronic diseases).

To date, I have worked with 'traditional' farming populations of the Andes of Peru and Ecuador, animal herding groups of Siberia and farmer and foragers of the jungles of Bolivia. In each place, many of the basic research questions have been the same: how have these populations adapted to their particular dietary and nutritional environments, and how ongoing patterns of lifestyle change and 'modernization' influences their diets and nutritional health.

Beyond the field research portion of my work, I also draw on comparative information from other primates and the human fossil record to model how our ancestors lived and survived in the past. What is clear is that food and nutrition were critically important factors that promoted the evolution of many unique human characteristics: for example, our big brain and our upright, 'bipedal' locomotion.

Ultimately, these are the issues that drew me to study Paleolithic diets. Seeing that nutrition has been such an important force of human evolution, and seeing that an evolutionary perspective on nutrition can also be helpful for understanding and dealing with modern day health problems like obesity, diabetes and other chronic diseases.

Q. What were your findings?

A. Broadly, our work has shown that throughout most of our evolutionary past and among tradition subsistence-level (i.e., food producing) populations today, food availability was marginal, and populations had to work much harder to obtain food and stay alive. Our work with traditional foraging, farming and herding populations has shown that these populations typically expend more calories over the course of a day than people in modern, urban societies.

These differences between 'traditional' and 'modern' life ways were clearly evident in the 'I Caveman' project. Over only a 10-day period, the group members lost an average of 13.6 pounds. Part of this weight loss reflected limited food availability; however, part of it also reflected the fact that they were spending many more calories living as Stone Age hunter-gatherers (an extra 500 calories a day for the men, and an extra 250 to 300 calories a day for the women).

Q. What exactly is a Paleolithic diet, and how can it be translated to modern-day eating?

A. Paleolithic diet refers to dietary patterns of human hunting and gathering populations from the Stone Age (up to 10,000 years ago). The term was coined in a famous paper from the New England Journal of Medicine in 1985.

The reconstruction of Paleolithic diets potentially gives us an idea about what humans were eating throughout most of our evolutionary history. This is the central idea of evolutionary approaches to health and nutrition: that many of our health problems today reflect an imbalance between our current dietary and lifestyle patterns and the conditions we adapted to throughout most of our evolutionary history.

Q. Tell us about the television show, 'I Caveman.' How did it work?

A. The program was shot out in Colorado. For the program, 10 people (six men and four women) were selected and provided with training in basic tool making, how to make fire and foraging hunting strategies. They were given traditional and primitive clothing, like skins and hide boots. For 10 days, they lived as Stone Age hunter-gatherers, using basic Paleolithic technology to obtain food.

There was at least one camera crew on the group at all times. I served as the expert on nutrition and health. Before they started, we collected baseline nutrition and health measures (like height, weight, percentage of body fat, resting metabolism, grip strength, blood pressure, cholesterol, glucose and hemoglobin levels). We then collected the same measurements at the end to see how well they did.

Two of the participants (one man and one woman) did not complete the entire 10-day experiment. We measured them immediately after they quit.

Q. How do you hope to expand your research?

A. We have continuing research among rainforest populations of Bolivia and among indigenous horse and reindeer herders of Siberia. In both places we are tracking how people's health changes over time in response to changes in lifestyle and environment.

There is talk of doing another 'I Caveman'-type show, in a different environment.

Q. How does your research relate to the obesity crisis in the United States? Why do you think Americans are so obese?

A. Rates of obesity in U.S. adults today are about 33 percent, which is 2.5 to three times what it they were in the 1960s. In discussing our obesity problem, most of the attention is focused on food intake alone. This is certainly a problem. However, the available data indicate the calorie intakes have increased only modestly over the last 40 to 50 years. What are generally ignored are changes in activity and energy expenditure.

This is where the evolutionary/Paleolithic perspective is helpful. It highlights the fact that our obesity problem is not simply a problem of too much food or what we eat, but also a problem of limited activity and exertion in our daily lives. So many of the elements of our modern lives, like cars, elevators, dishwashers, heating and cooling our houses, reduce the energy, or calories, we spend just to stay alive.