A new way of calculating our biological age based on the bacteria in our gut has thrown up some surprising results. Among other things, it suggests that people following the paleo diet are nearly two years 鈥渙lder鈥� on average compared with people not on the diet.
鈥淚t is striking,鈥� says Guruduth Banavar at , a California-based company that sells tests that measure gut bacteria. 鈥淚n our population, people on a paleo diet were younger, but their biological age is actually older.鈥�
In the past decade, many groups have developed ways of estimating people鈥檚 age based on biomarkers such as the length of telomeres. These estimated biological ages are thought to reveal whether people are ageing slower or faster than normal, though it has yet to be shown that biological age is an accurate predictor of life expectancy.
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Several groups have been trying to estimate age by using machine learning to analyse microbiome data. Viome鈥檚 approach involves looking at which genes are active in gut bacteria, not simply which genes are present, as other groups do, says Banavar.
Its findings are based on 90,000 stool samples collected and analysed by the company, making it by far the largest such study to date. Another study out last year, for instance, was .
Because they have so many samples, the researchers have been able to look at how various lifestyle factors affect biological age as estimated by their method. For example, they could examine the effects of following the paleo diet, in which people eat as our Palaeolithic ancestors are supposed to have done.
鈥淔or the paleo diet, the finding is quite strong,鈥� says team member Hal Tily. 鈥淚t鈥檚 unambiguous that something is going on.鈥�
However, this could be because people with poor health are more likely to try the paleo diet, rather than this being a result of the diet itself, cautions Cara Frankenfeld at George Mason University in Virginia. 鈥淲e can鈥檛 identify whether something about a person鈥檚 health made them decide to change their diet or whether the diet preceded and influenced the biological age,鈥� she says.
The team also found that people on the low-carb, high-fat ketogenic diet had biological ages nearly two years older on average, but this finding isn鈥檛 as robust as the paleo diet one, says Tily.
Women who reported drinking more than a unit of alcohol a day, and men who drink more than two units a day, were nearly a year older on average. People who say they eat organic food were around half a year older.
Vegetarians fared best, being around a year-and-a-half younger biologically than non-vegetarians on average. This finding isn鈥檛 surprising given all the evidence that a vegetarian diet is beneficial, says Banavar, but he stills thinks it is significant.
鈥淭his is the first time that anybody has shown through biological ageing modelling that this effect is true at a population level,鈥� he says. Vegans were also younger biologically, but not quite as much as vegetarians.
鈥淔rom a machine-learning perspective, the methods look sound,鈥� says James Cole at University College London, who has estimated biological age from brain scans. However, Cole says the microbiome method is much less accurate at estimating actual ages than other methods.
Methods for calculating biological age don鈥檛 necessarily need to be highly accurate, says Steve Horvath at the University of California, Los Angeles. If estimated biological ages exactly matched people鈥檚 actual ages, it would not tell you anything interesting, he says.
鈥淭his data looks very promising,鈥� says Horvath. But Viome鈥檚 approach needs to be validated by independent groups, he says.
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