to find a more realistic path, i'm at the massachusetts institute of technology to meet a pioneer in longevity research, dr. leonard guarente. he's taking on a big problem that most everyone will eventually face. - as you get older, you lose muscle mass and you gain fat mass. - okay. - and both of those things are bad. - sure. lenny is a firm believer in the power of exercise to keep our bodies healthier for longer. - by impacting aging, you can not only improve health, but help mitigate diseases. - [maren] at his cutting edge lab, his team identified the first longevity gene and this breakthrough opened the door to the possibility that we might one day control the aging process in the human organisms. - i think the best case scenario is attempting really to maintain what we call health span. if people live healthier lives for as long as possible and really compress morbidity to a very short period at the end of life, that's mgoal. - instead of slowly declining in our sixties, plagued by things like heart disease, dementia and cancer, lenny thinks we could live until 90 and then make