Unfortunately, many humans are moving in the opposite direction. As obesity reaches epidemic rates in Western countries, Fontana says rather than closing the 30-year gap between healthspan and lifespan, the gap is likely to grow. It's even possible lifespan may decrease as people develop preventable diseases such as atherosclerosis, type 2 diabetes and certain forms of cancer.

Those growing rates of obesity are a reason some scientists think calorie restriction will never catch on, regardless of its potential benefits. But, Fontana says, if researchers who study nutrition and aging can understand how calorie restriction lengthens life and makes people healthier, it may be possible to develop less drastic interventions or medicines that influence pathways affected by calorie restriction and help keep people healthy as they get older.

Among people now practicing calorie restriction, he says side effects include reduced libido because calorie restriction reduces testosterone levels. They also tend to become cold more quickly because their thermal regulation changes as their metabolism slows and their core body temperature drops.

Fontana says as calorie restriction research advances on many fronts, it's becoming clear that dietary advice once based on epidemiological data now makes sense from a molecular point of view. In the past, dietitians might recommend more fruits and vegetables or less meat and more whole grains. They based that advice on studies showing people who ate more vegetables or fewer animal products tended to have less cardiovascular disease.

"Now we have moved from epidemiology to molecular biology," he says. "We know that certain nutrients, as well as lower calorie intake, can influence IGF-1 and other pathways. Soon we hope to be able to use that knowledge to help people live longer and healthier lives.

Source: Washington University School of Medicine