快猫短视频

Permanently cutting calorie intake may slightly slow the rate at which we age, according to a new study based on one of the few randomised trials investigating this method. But while this may sound appealing, it could be too soon to draw firm conclusions from the study. The tests used to measure rates of ageing didn鈥檛 all produce promising results. They are also still relatively new research tools and perhaps not ready for mainstream use.

The trial looked at an anti-ageing strategy that has shown promising results in animals: a permanent reduction in calorie intake. In mice, this extends their lifespan by as much as 50 per cent.

But we don鈥檛 yet know if calorie restriction has the same effect in people, because humans live so much longer than other animals and it is notoriously hard to stay on a calorie-restriction diet for extended periods.

In 2007, the US National Institutes of Health (NIH) began a trial in which 220 non-obese adults were randomly chosen to try to reduce the number of calories in their existing diet by 25 per cent or to eat what they liked. They were monitored for two years.

One interesting finding was that, although the calorie-restricted group were given intense support and coaching on what kind of food to eat, they didn鈥檛 achieve the desired calorie shortfall. On average, they managed about a 12 per cent cut, showing just how difficult it is to stick to such a change.

By several measures, the dieters , seeing reductions in their weight, blood pressure and cholesterol levels. But this doesn鈥檛 tell us if their ageing slowed. The people were aged between 21 and 50 when they started the experiment and therefore were extremely unlikely to die from age-related conditions such as heart attacks and cancer over the two years, no matter what their calorie intake.

In the new study, at Columbia University in New York and his colleagues took a different tack, carrying out several tests on blood samples that had been taken from the participants during the NIH trial.

Belsky鈥檚 team sought to find out if their 鈥渂iological age鈥� differed from their chronological age. The idea is that someone who has been alive for 50 years, for instance, could have a biological age of 40, if they have been living healthily and are likely to live for 10 years longer than average.

Several firms have developed commercial tests to assess biological age, which measure multiple biochemicals in the blood, sometimes combining them with other general health indicators, such as smoking history. According to two of these tests carried out by Belsky鈥檚 team, the diet had no effect on the participants鈥� biological age.

But there was a small difference recorded by a third test, one developed by Belsky鈥檚 team and based on patterns of chemical modifications to people鈥檚 DNA, called epigenetic changes. Several studies have shown that the patterns of epigenetic modifications change as we get older, although exactly which parts of our DNA are affected and why is still unclear.

Belsky鈥檚 assay doesn鈥檛 measure current biological age, but the rate at which someone鈥檚 biological age is rising. It is called the test because it was developed using results from a large, ongoing study of people from Dunedin in New Zealand.

In the trial, those in the calorie-restriction group showed a slightly reduced speed of ageing, slowed by between 2 per cent and 3 per cent, as measured by the DunedinPACE test. That might sound a small difference, but modelling based on the Dunedin research and other studies suggests it would translate into about a 10 per cent to 15 per cent lower risk of death over 13 years.

Belsky told 快猫短视频 that the difference in results between the three tests could be because the DunedinPACE test is more sensitive to the small effects generated by the calorie-restriction diet.

But other researchers say the conflicting results from the three tests used in the new study is confusing. 鈥淭he tests don鈥檛 agree with each other,鈥� says at City of Hope in Duarte, California.

Unfortunately for those keen to lengthen their lifespan, we won鈥檛 know if any of the biological ageing tests really work until studies have gone on for many years and show that people with an apparently lower biological age really do live for longer. That means it will also be a long time before we know if calorie restriction slows ageing.