These monkeys dieted so that you don’t have to. It turns out that calorie restriction – a long-term reduction in energy intake – isn’t the elixir of life.
For years now, the promise of dramatically extended life has been dangled before us (and, more importantly, before venture capitalists, who know a lucrative market when they see one). Futurists frequently declare that some people alive today will never die.
Perhaps the appeal of the idea is inevitable. As human beings, we are the only species known to be consistently aware of our looming demise. According to those who work in an academic discipline known as terror management theory, the foreknowledge of inescapable death colours virtually everything in our lives.
However, it’s the monkeys that most deserve our sympathy. For 25 years, scientists have been putting rhesus monkeys on a restricted calorie intake, giving them only 70 per cent of the calories fed to a control group. And all in vain: they didn’t live as long as anyone hoped.
Studies of worms had suggested that calorie restriction makes a vast difference to longevity – research has shown that certain worms will live twice as long on a restricted diet. One of the early worm studies was by Cynthia Kenyon of the University of California, San Francisco. As soon as she saw that putting sugar on the worms’ food led to a reduction in their lifespan, she stopped eating carbohydrates.
The thinking behind the hope is fairly straightforward. Food intake is related to insulin production, and the body’s insulin receptors dictate what happens with scores of genes known to affect the ageing process. Change the way you eat (or take a pill that mimics the effects of drastic changes to your diet) and you can change the age at which you die.
It seemed a good idea. Follow up studies in rats and mice, which are relatively close to primates in evolutionary terms, also showed increased longevity associated with calorie restriction. The rodents had improved health, more vitality and shinier coats. Even better, a 20-year study of rhesus monkeys on restricted diets, led by scientists in Madison, Wisconsin, came to the same conclusion in 2009.
Science, however, is rarely so straightforward. The research, it turns out, was flawed. A study published in Nature at the end of August shows that, once you take the genetic variety of monkeys in the trial into consideration, the impact of calorie restriction on lifespan is not so amazing. What’s more, the ones on the restricted diet programme got their calories from different kinds of food from those in the all-you-can-eat control group. It was something of a “duh” moment: who doesn’t know that healthy eating isn’t just a matter of calorie-counting?
Piece of cake
So, the promise of extended life has taken a battering, but we had already been warned that it was all probably too good to be true. In 2002, a group of 51 researchers came out against simple solutions, issuing a “position statement” that declared human ageing unlikely to be the result of any controllable genetic program.
At the time, with all the excitement about the new data – including rodents so long-lived, they were dubbed “Methuselah Mice” – they seemed like killjoys. But maybe their instinct was right.
The best we can say now is that it’s all more complicated than we thought – and that moderation is the key. According to the results of a study of centenarians, the people who live longest are of average weight: “a chubby bunch”, as the gerontologist Nir Barzilai told Nature News. So, yes, summer’s over; winter’s coming. And you’re still going to die. But cheer up and have a bit of cake. It’s what the monkeys would have wanted.
Michael Brooks’s “The Secret Anarchy of Science” is published by Profile Books (£8.99).