In 1935, in the labs of Cornell University, a discovery was made that should have taken the world by storm.
It was all thanks to Prof Clive McCay, an American nutritionist, and a group of rats. Or rather, several groups of rats – McCay had split the rodents up, allowing some to eat as much as they wanted while the others lived on substantially reduced rations.
After 30 months, all the rats that were allowed to eat what they liked had died. But just under half of the animals on the restricted diet were still going strong. In fact, by the end of the experiment, McCay found that the carefully restricted diet almost doubled the average lifespan of a rat.
You might worry that the calorie-counting animals were doddering along, unable to summon the energy even to die long after their well-fed brethren had copped it. This wasn’t the case: the restricted diet rats were also healthier. They mostly evaded cancer, had fewer lung and kidney problems and even had silkier fur.
Overall, McCay’s findings suggested it might be possible to influence the ageing process through diet – that what you eat could effectively slow your ageing on a biological level.
This absolutely remarkable finding didn’t really go anywhere for decades – perhaps because US life expectancy at the time was just 60 years. Fewer people would have been concerned with ageing well, simply because far fewer of them could look forward to ageing at all.
Fortunately for us, this area of science has seen a resurgence of interest in recent years. Results similar to McCay’s have now been seen in other animals, from worms and flies to trout and dogs.
We can also now study mice on restricted diets and see that their ageing is indeed slowing down by looking at the ticking of their ‘epigenetic clocks’ (a popular method of measuring biological age) or the shortening of their telomeres (the protective caps on the ends of DNA that shorten as a living organism gets older).
Something similar may well apply to humans. In fact, some scientists estimate that switching from a typical US or UK diet to an ‘optimal’ diet could add anything from a few years to a decade to life expectancy.
All of this means that we’ve got pretty compelling evidence that what we eat can have an effect on the ageing process. It may be possible, in other words, to eat smarter and live longer as a result.
But rats and trout aren’t human beings, and the simple measures that could help them live longer won’t necessarily work for us. So what will?
There’s a lot of conflicting research out there and plenty of potentially damaging fad diets. But there are some ways of eating that have repeatedly been shown to give you the best chance of living a longer and healthier life.
1. Get the chemistry right
In 1677, Dutch biologist and microscopy pioneer Antonie van Leeuwenhoek was looking for more things to examine using his new magnifying device and was persuaded by Secretary of the Royal Society Henry Oldenburg to try semen. His first discovery was the sperm cell – though he called them ‘animalcules’ and their true function wouldn’t be uncovered for almost two centuries.
He also noticed that, as the semen was drying out, tiny crystals began to form. These crystals were later dubbed ‘spermidine’ and we now think that spermidine might have anti-ageing properties. Why? Because it activates a process known as autophagy, whereby cells scavenge old, faulty components for spare parts, giving themselves an anti-ageing spring clean in the process.
Despite the name, and the history behind its discovery, spermidine is a chemical that’s actually found throughout the natural world, not just in semen: foods particularly rich in it include soybeans, mushrooms and cheddar cheese.
Experiments in mice show that adding the compound to their water can make them live longer and people who get the most spermidine in their diets have been shown to live up to five years longer on average than those who consume the least.
There are other natural molecules found in foods that could have anti-ageing properties. Curcumin, one of the chemicals that gives turmeric its yellow colour, may have anti-inflammatory effects and is being investigated as a possible adjunct to cancer treatment.
Similarly, quercetin (found in various foods including elderberries, red cabbage and dark chocolate) and fisetin (found in fruits such as strawberries) are both ‘flavonoids’ that have been found to clear out ‘old’ cells in mice.
A word of caution here: there’s no such thing as a ‘superfood’, and singling out this, that or the other magic molecule as a health-giving elixir that means we should all binge on a particular kind of berry is bad, reductive science. That said, there’s probably no harm in munching on a few extra mushrooms or red cabbage leaves.
2. Eat more vegetables
The biggest takeaway from two major studies into how changes in diet affect life expectancy was that we should eat more vegetables and plant-based foods. Specifically, eating more whole grains (like wholemeal bread or brown rice, as opposed to the ‘refined’ white alternatives), legumes (peas, beans and pulses) and nuts could add a few more years to your life expectancy.
Additionally, the researchers found that eating too much red and processed meat could have a negative impact, as could drinking too many sugar-sweetened beverages. In fact, moving from the current average consumption of meat and sugary drinks to the optimal level could add three years to your life expectancy.
And what is the optimal level of processed meat and sugary drinks? According to both studies, none at all.
You can take all these findings with a tiny pinch of salt, however – especially as excessive sodium chloride consumption is associated with premature death. That’s because the biggest and best studies of long-term health and lifespan face a big challenge: they’re observational.
This means they simply ask people what they eat and follow them for decades to see how long they live. As a result, other factors about participants’ lives could be overlooked.
For instance, such studies show that vegetarians live longer, but is that because vegetables are healthier than meat or because veggies and vegans are likely to be more health-conscious in other ways?
The gold standard would be randomised trials that split people into several diet groups, but to avoid being too expensive (and unethical), experiments of this kind generally only take place over a few weeks or months, rather than years.
The studies of this sort that have been undertaken so far do back up the big observational studies in terms of short-term markers of health, such as improvements in blood tests. And again, one systematic review found that the best foods for improving blood markers were nuts, legumes and whole grains, while the worst were red meat and sugar-sweetened beverages.
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3. Pay attention to your source of protein
Thanks to studies carried out on various animals – including on worms and flies – scientists have found that restricting protein intake could be the key to a longer life in animals.
In humans, though, the evidence requires a closer look. One major study in 2014 suggested that people eating less protein lived longer than those with a high-protein diet: a 50-year-old eating less than 45g of protein per day could expect to live to 82, while one eating 90g per day would only make it to 78.
This could be because high-protein diets increase levels of a pro-growth hormone called IGF-1, which, as well as building muscle, is also known to accelerate the ageing process and could increase the risk of cancer.
There are a couple of issues with this theory, however. Firstly, after the age of 65 or so, the effect reversed, and those eating more protein lived longer than those eating less. This is perhaps because protein helps us with the vital task of maintaining muscle mass as we get older.
Secondly, when the authors examined animal and plant protein separately, the effect in middle age disappeared. So perhaps it’s the other ingredients found in meat (especially red and processed meat) that cause the increased risk of cancer and death, rather than the protein itself.
Indeed, a huge review of 32 studies looking at protein consumption found that higher protein consumption decreases risk of death overall – although a diet that substitutes plant protein (think nuts, seeds, legumes and soy products) for meat protein could be associated with longevity.
4. Reduce visceral fat
We’ve all been told countless times that we should try to maintain a healthy weight. Looking at the biology of ageing, though, really underscores why this is so important.
For one thing, it’s estimated that every extra five body mass index (BMI) points could knock a few years off your life expectancy. It’s hard to give precise estimates, not least because BMI is an imperfect metric – it can’t tell the difference between fat and muscle. But there is an explanation for this statistic.
We now know that fat – and particularly ‘visceral’ fat, which builds up between the organs inside your body, as opposed to the ‘subcutaneous’ fat that accumulates under your skin – emits a cocktail of inflammatory molecules that can speed up the ageing process.
Chronic inflammation is both a cause and consequence of ageing, so being overweight is a little like ageing at an accelerated rate. This means that being overweight increases the risk of many different diseases that become more common as we get older, from heart disease and diabetes to some kinds of cancer.
It can, of course, be pretty challenging to lose weight and visceral fat, but the good news is that there doesn’t seem to be a single ‘best’ diet when it comes to doing so.
Studies pitting various weight-loss diets against one another (low-fat vs low-carb, for instance) have found that, as long as you eat less, it doesn’t matter exactly what it is. Find something that’s healthy and works for you, rather than worrying about what the perfect weight-loss diet might be.
5. Not so fast with the fasting
While touted as an anti-ageing miracle by many online influencers, the evidence for the benefits of fasting is hardly clear-cut. Studies on smaller animals (such as McCay’s) appear to show that cutting the calorie intake of animals can lengthen their lifespan. But, as we’ve already noted, humans aren’t just big mice – so does the same necessarily apply to us?
In fact, when calorie restriction was tried on rhesus monkeys, which are far closer to us than rats in both evolutionary and lifespan terms, the effects were much weaker. The monkeys eating less showed a decent extension of ‘healthspan’ – the length of life spent in good health – but didn’t seem to live much longer if already eating a basically healthy diet.
The handful of studies carried out in actual humans have been too short to give a clear answer. A couple of years’ dietary restriction in people resulted in improved blood test results, but also side effects ranging from anaemia (where a deficiency of red blood cells leaves your tissues short of oxygen) and loss of sex drive to irritability and feeling cold.
The final piece of bad news? That hunger you feel when restricting your diet will never go away. As anti-ageing scientists joke, while dietary restriction probably won’t make you live longer, it will certainly feel like it.
But what about intermittent fasting? What if we could get some of the benefits of eating less all the time, but without the constant hunger? The theory is that not having enough protein coming in promotes autophagy, the cellular recycling and repair process.
Could we activate such mechanisms by not eating at all for a period of time, but without cutting back on calories overall?
In short, probably not.
The evidence is similarly thin whether we look at time-restricted feeding (where you only eat in a certain window during the day, often six or eight hours – one way you can achieve this is by skipping breakfast), the 5:2 diet (where you eat nothing or a substantially reduced amount on two non-consecutive days a week) or even periodic fasting (whose adherents consume only water for five-plus days every few months).
While intermittent fasting can be an effective weight-loss strategy in the short term, there is a hidden pitfall: studies show that people who fast can lose a greater percentage of muscle mass than people adhering to a consistent low-calorie diet. Since strong muscles are critical for health while ageing, this is potentially a red flag.
6. Give diet pills a miss... for now
Despite the claims you might see on social media, there’s no pill or supplement with outstanding anti-ageing properties that has been extensively tested on humans. There are several exciting prospects in the pipeline, however.
One such is rapamycin, a drug currently used for organ transplant patients that makes mice live 10 per cent longer, even if started at an older age. It does so by activating autophagy, the same cellular repair and recycling process seen when cutting back on food.
Then there’s semaglutide (also known by its trade names Ozempic and Wegovy). While it’s currently used by humans to curb appetite, it’s also been shown to reduce the risk of cardiovascular disease in old age. Yet whether these effects are health-improving, anti-ageing or just side-effects of the weight-loss it causes needs further investigation.
Even more treatments could be on the way. The lessons from dietarily restricted animals should allow us to bottle more of their biology, perhaps using drugs or gene therapy to turn back our biological clocks. Perhaps the greatest gift that ageing biology will give us – apart from longer, healthier lives, obviously – will be freedom from endless fad diets, and the dodgy doctors and health influencers peddling them.
For now, though, if you want to stay healthy enough for long enough to enjoy the anti-ageing drugs that are currently in development, adopting an anti-ageing diet is an excellent way to start.
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