Calorie restricted monkeys lead a longer, healthier life
Nearly four decades after they began, two long-running but conflicting studies reached a consensus.
Rhesus macaques that eat fewer calories live longer than their free-feeding counterparts, two long-running US studies report in Nature Communications.
The research groups – one from the University of Wisconsin-Madison and the other from the National Institute on Ageing – have, for years, reached contradicting conclusions when it comes to ageing and food intake. But new analyses of both studies show that calorie restriction does seem to prolong macaque lifespan and – perhaps more importantly – highlight how different methods and subjects can vastly affect a study's outcome.
As human ageing goes, the rhesus macaque (Macaca mulatta) is a pretty good model. We share around 93% of their genome and they mature much like us: their hair greys and they start balding, for instance, and they show cognitive decline as they age.
So in the 1980s, the University of Wisconsin-Madison and the National Institute of Ageing each started long-term studies to see how calorie restriction – that is, feeding them less energy without malnutrition – affected the macaques' health and life.
In 2009, the University of Wisconsin-Madison reported their calorie-restricted subjects lived longer and were healthier. But in 2012, the National Institute on Ageing found that while there was a trend towards better health in calorie-restricted macaques, it wasn't statistically significant – and they didn't live longer than the control group, the non-calorie-restricted macaques.
In the new paper, the teams compared methodologies and found a number of differences that explained their conflicting results.
The macaques were calorie-restricted at different ages. It turns out that calorie restriction is more beneficial in older primates than younger.
The older macaques in the control group housed at the National Institute of Ageing ate significantly less than those at the University of Wisconsin-Madison too. This, the researchers reason, bestowed upon them benefits and decreased any difference between the calorie-restricted and control groups.
Macaques were also fed different diets. At the National Institute of Ageing, the subjects ate naturally sourced foods while those at the University of Wisconsin-Madison dined on processed, sugary food. Unsurprisingly, this meant the latter control group was fatter than their National Institute of Ageing counterparts.
The groups were also from different genetic stock. The National Institute of Ageing macaques were Chinese and Indian, while the University of Wisconsin-Madison monkeys were solely Indian.
So what does this mean for you and me?
The work isn't proof that caloric restriction slows the biological ageing of the macaques, nor does it reveal the minimum degree of calorie restriction that provides maximum benefits.
Sex also played a role, with female macaques less vulnerable to the negative effects of being fatter than males.
Still, the researchers write that exploring factors around calorie restriction will be "pivotal in bringing these ideas into clinical research and human health care".