And they weren\u2019t struggling on, too hungry to muster the energy to die. These rats were, in fact, healthier in their old age, with better-looking lungs and kidneys and no cancer (until the rats\u2019 food supply was increased again right at the end of the experiment).<\/p>\n
In the intervening century or so, we\u2019ve found that cutting back calories can have life- and health-extending effects across the tree of life: from single-celled fungus yeast, to nematode worms, flies, spiders, grasshoppers, guppies, trout, mice, hamsters and dogs.<\/p>\n
Why? The theory is that reduced food intake might push a biological button inside our cells, telling them to hunker down.<\/p>\n
If snacks are scarce, it makes little sense to burn calories by, for example, gearing up for reproduction. This is an energetically expensive process with the added disadvantage that your offspring would be born into a world without enough food.<\/p>\n
Instead, evolution<\/a> would prefer that an animal in this situation preserves its energy and reproduce another day. Instead, the body slows the ageing process, improving the odds that you\u2019re still biologically young and fit enough to reproduce when food returns.<\/p>\n The anti-ageing effects of eating less food<\/p>\n While there\u2019s a decent weight of evidence for calorie restriction in animals, data in humans are harder to come by.<\/p>\n Funders, ethics committees and participants are understandably reluctant to sign off on the forcible adoption of multi-decade meal plans.<\/p>\n The biggest trial to date was the so-called CALERIE trial<\/a> (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy \u2013 see what they did there?), where participants aimed to cut back their intake by 25 per cent for two years.<\/p>\n (In practice, the average reduction was just 12 per cent \u2013 an indication of how hard diets like this are to maintain, even with a lot of help from scientists.)<\/p>\n Two years is obviously far too short a time to determine if it made people live longer, but they did lose an average of 8kg (17.6lb), and saw modest reductions in LDL cholesterol, blood pressure, blood sugar and markers of inflammation.<\/p>\n Trimming the protein from your diet<\/p>\n There\u2019s another question that\u2019s perhaps even more important if you want to put this idea into practice yourself: what exactly should you be cutting back on?<\/p>\n Recent research suggests that we actually need to eat less of the current health influencer darling: protein.<\/p>\n For instance, one study<\/a> from The University of Sydney suggested mice on a low-protein diet lived about 30 per cent longer than those fed protein-rich chow.<\/p>\n It might even get more specific than that. Proteins are made up of 20 chemical building blocks called amino acids, and cutting back on one or more of them can be enough to increase lifespan.<\/p>\n Research has found<\/a> that cutting back on \u2018branched-chain\u2019 amino acids (BCAAs, named after the shape of their chemical structure) can make male mice live 30 per cent longer. (Why it doesn\u2019t work in female mice is unknown.)<\/p>\n Cutting back specifically on isoleucine, another amino acid, helped male mice live 33 per cent longer (but female mice just 7 per cent).<\/p>\n Research into other amino acids, however, shows<\/a> that it\u2019s a delicate balance. Take methionine, for instance.<\/p>\n Mice fed a diet containing 0.15 per cent of this amino acid lived a whole 10 per cent longer than mice eating a more typical 0.4 per cent methionine diet.<\/p>\n Mice in the same study were also fed 0.1 per cent methionine and died early, often with rectal prolapse \u2013 I think I\u2019d rather die of old age than run the risk of that happening.<\/p>\n Recent work has switched from restricting dietary components to trying to optimise them instead. The challenge is that, with 20 amino acids, the number of combinations rapidly becomes overwhelming.<\/p>\n Even if you wanted to try just \u2018high\u2019 and \u2018low\u2019 amounts of each amino acid in combination, that would require over a million experiments.<\/p>\n Read more:<\/p>\n The amino acid diet based on your DNA<\/p>\n Scientists have tried to sidestep this problem by looking into our DNA<\/a>, which contains the instructions for building proteins. The LEGO bricks that make up proteins are amino acids.<\/p>\n What if we provide an organism with a diet whose amino acid ratio directly mirrors the proportions found in the DNA?<\/p>\n An initial study<\/a> in fruit flies found that those on the DNA-matched diet grew bigger, grew faster, laid more eggs and lived longer than the flies who were fed regular food.<\/p>\n Follow-up work has taken place in mice \u2013 when fed the ideal dietary amino acid ratio found in their DNA, they grew bigger faster, and the male mice had more muscle and better sperm production.<\/p>\n But we don\u2019t yet know whether these mice will also live longer.<\/p>\n What might be happening biologically when protein is cut from a diet is unclear, but scientists are starting to pull back the curtain. Like straightforward calorie restriction, it seems to slow down the ageing process pretty broadly.<\/p>\n A new paper<\/a> published in May 2025 even suggests that low-protein diets could reduce damage and mutations in DNA.<\/p>\n The suggestion isn\u2019t that protein directly causes mutations, but that its effect on an organism\u2019s metabolism results in the production of \u2018free radicals\u2019 that can cause damage to DNA and other molecules in our cells.<\/p>\n Mutations in DNA are known to cause cancer and have long been suspected of having a more general role in the ageing process.<\/p>\n The idea that dietary changes could indirectly affect something as fundamental as the rate of these chemical \u2018typos\u2019 appearing in our DNA is worth exploring.<\/p>\n Some people need more protein<\/p>\n So, should you start cutting back on protein? While the animal data is suggestive, results in humans are more mixed.<\/p>\n![\"Illustration](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/03\/protein-sweet-spot-Rapamycin-inhibiting-mTORC1-illustration.jpg\")
Rapamycin (red) switches off a protein called mTOR (blue), which is closely linked to ageing – Image credit: Science Photo Library<\/p>\n