In a restaurant setting sometime in the not-too distant future, a man and a woman are on their first date. After the initial nerves subside, all is going well.
The man is 33, he says, has been single for most of those years, and, although he doesn’t mention it, knows he is looking to settle down and have a family. The woman replies that she is 52, has been married, divorced, and has children in their early 20s. He had no idea – she looked his age, or younger.
This is a dream of Julie Mattison from the National Institute on Ageing (NIA) in the United States. She envisions a time when chronological age ticks by with every year, but biological age can be set to a different timer, where elderly doesn’t mean what it does now.
It sounds far-fetched, but our society has already made great strides towards that goal, thanks to advances in medicine and improvements in healthy living. In 2014, for instance, the United States Health Interview Survey reported that 16% of people aged between 50 and 64 were impaired every day with chronic illness. Three decades earlier that number was 23%. In other words, as well as benefiting from longer lifespans, we are also experiencing longer “healthspans” – and the latter is proving to be even more malleable. To paraphrase and update a speech from John F Kennedy given at the first White House Conference on Ageing in 1961, life can indeed be added to years, rather than just years added to life.
So, what do we need to do to enhance the length and quality of our lives even more? Researchers worldwide are pursuing various ideas, but for Mattison and colleagues, the answer is a simple change in diet. They believe that the key to a better old age may be to reduce the amount of food on our plates, via an approach called “calorie restriction”. This diet goes further than cutting back on fatty foods from time-to-time; it’s about making gradual and careful reductions in portion size permanently. Since the early 1930s, a 30% reduction in the amount of food consumed per day has been linked to longer, more active lives in worms, flies, rats, mice, and monkeys. Across the animal kingdom, in other words, calorie restriction has proven the best remedy for the ravages of life. And it’s possible that humans have just as much to gain.
The idea that what a person eats influences their health no doubt predates any historical accounts that remain today. But, as is often the case for any scientific discipline, the first detailed accounts come from Ancient Greece. Hippocrates, one of the first physicians to claim diseases were natural and not supernatural, observed that many ailments were associated with gluttony; obese Greeks tended to die younger than slim Greeks, that was clear and written down on papyrus.
Spreading from this epicentre of science, these ideas were adopted and adapted over the centuries. And at the end of the 15th Century, Alvise Cornaro, an infirm aristocrat from a small village near Venice in Italy, turned the prevailing wisdom on its head, and on himself.
If indulgence was harmful, would dietary asceticism be helpful? To find out, Cornaro, aged 40, ate only 350g (12oz) of food per day, roughly 1000 calories according to recent estimates. He ate bread, panatela or broth, and eggs. For meat he chose veal, goat, beef, partridge, thrush, and any poultry that was available. He bought fish caught from the local rivers.
Restricted in amount but not variety, Cornaro claimed to have achieved “perfect health” up until his death more than 40 years later. Although he changed his birthdate as he aged, claiming that he had reached his 98th year, it is thought that he was around 84 when he died – still an impressive feat in the 16th Century, a time when 50 or 60 years old was considered elderly. In 1591, his grandson published his posthumous three-volume tome entitled “Discourses on the Sober Life,” pushing dietary restriction into the mainstream, and redefining ageing itself.
With an additional boost of health into the evening of life, the elderly, in full possession of their mental capacities, would be able to put decades of amassed knowledge to good use, Carnaro claimed. With his diet, beauty became the aged, not the youthful.
Cornaro was an interesting man but his findings are not to be taken as fact by any branch of science. Even if he was true to his word and did not suffer ill health for nearly half a century, which seems unlikely, he was a case study of one – not representative of humans as a whole.
But since a foundational study in 1935 in white rats, a dietary restriction of between 30-50% has been shown to extend lifespan, delaying death from age-related disorders and disease. Of course, what works for a rat or any other laboratory organism might not work for a human.
Long-term trials, following humans from early adulthood to death, are a rarity. “I don’t see a human study of longevity as something that would be a fundable research programme,” says Mattison. “Even if you start humans at 40 or 50 years old, you’re still looking at potentially 40 or 50 more years [of study].” Plus, she adds, ensuring that extraneous factors – exercise, smoking, medical treatments, mental wellbeing – don’t influence the trial’s end results is near impossible for our socially and culturally complex species.
That’s why, in the late 1980s, two independent long-term trials – one at NIA and the other at the University of Wisconsin – were set up to study calorie restriction and ageing in Rhesus monkeys. Not only do we share 93% of our DNA with these primates, we age in the same way too.
Slowly, after middle age (around 15 years in Rhesus monkeys) the back starts to hunch, the skin and muscles start to sag, and, where it still grows, hair goes from gingery brown to grey. The similarities go deeper. In these primates, the occurrence of cancer, diabetes, and heart disease increases in frequency and severity with age. “They’re an excellent model to study ageing,” says Rozalyn Anderson, a gerontologist from the University of Wisconsin.
And they’re easy to control. Fed with specially made biscuits, the diets of the 76 monkeys at the University of Wisconsin and the 121 at NIA are tailored to their age, weight, and natural appetite. All monkeys receive the full complement of nutrients and minerals that their bodies crave. It’s just that half of the monkeys, the calorie restricted (or CR) group, eat 30% less.
They are far from malnourished or starving. Take Sherman, a 43-year-old monkey from NIA. Mattison says that since being placed on the CR diet in 1987, aged 16, Sherman hasn’t shown any overt signs of hunger that are well characterised in his species.