Dr. Valter Longo is a professor at the USC Davis School of Gerontology based in California, and the director of the USC Longevity Institute. He's also the author of the bestseller "The Longevity Diet," and an internationally recognized expert for his studies on the impact of fasting on healthy longevity. His laboratory focuses on the fundamental mechanism of aging as the basis of all age-related diseases, but also explores dietary interventions that can affect stem cell-based therapies that promote longevity.

In your bestselling book The Longevity Diet, you refer to the goal of staying young and healthy as long as possible. In this context, what is your definition of aging?

Dr. Longo: Well, in the book, I started talking about the necessity to focus much more on the period in which we stay young, what I call juventology. The aging process is just what we define, all the dysfunctions that accumulate that are time-dependent. So let's say if you have a car, the tires wear out, and you look at the mechanisms of why. That's interesting but to me, not as interesting as saying, maybe there is a program that once in a while changes the tires. I don't need to spend a lot of time figuring out why rubber gets worn out, just to replace the tires more often. So that's the difference between gerontology and juventology. In one case, you try to prevent things from getting older, and in the other case, you mostly try and focus on how we get older and to slow it down.

Your laboratory was the first one to prove that aging can be programmed. How can we initiate a healthy longevity program and where's the best place to start?

Dr. Longo: The best place to start is to look back at what I call three billion years of research and development and say there are systems out there that are alternative to the main one. For example, if you take a microorganism like the yeast that we use to make bread, you see that it has multiple programs. In one program, it tries to grow very fast, but it dies very quickly. In another, it doesn't grow anymore, but it lives in the fast lane, everything is very fast, and it lasts about six days. Then, in the third program, in which its metabolism slows down, it can go for about 15/17 days. Then there's a fourth program, called spore state and it can go on for years. So now that is a 100-fold difference, if not more between program one and program four. So my lab is always focused on thinking you could try to take any organism and do all kinds of things to try to extend life span by slowing down aging or you can try to tap into these preexisting programs and activate them. By combining tradition with technology you can come up with something that can be powerful and safe.

What do you think about a high-protein and high-fat diet?

Dr. Longo: Science focused on longevity is clear, proteins are not so good. You have to have enough, but you don't want to have an excess. Then you look at clinical studies, there are lots of data suggesting that people who have a high-protein diet can have different types of problems. Not in the short-run, but very high-protein diets can be problematic for the kidneys, etc. So high protein does not look very good in clinical tests. Then you go to epidemiological studies of large populations. What happens to people in the United States or Europe who eat a lot of protein versus those who eat low protein? In the majority of the studies, the people who have a low but sufficient protein diet do better, live longer and have fewer diseases. Then you look at centenarians and take some of the people that live the longest around the world. The great majority of them have a low-protein diet. Proteins tend to activate growth factors, which activate the function of every cell. So for example, if clinical studies have shown that people that have an insufficient protein diet, don't build muscle and are weak. So the ideal situation is to find things that don't have lots of short-term problems but provide long-term solutions.