Secret to a long life revealed - and it's not all about what you eat, study suggests

Living a long and healthy life may be more dependent on genetics than dietary choices alone, according to new research.

Although it is commonly thought that consuming fewer calories can extend lifespan, with some research suggesting a 25% reduction in caloric intake can slow down ageing by up to 3%, a recent study on mice indicates that genetics may play a more significant role in longevity than simply reducing food consumption.

The scientists involved in the study believe that certain genes, which have yet to be identified, may contribute to a longer lifespan by making the body more resilient in the face of adversity. The study found that the mice that lived the longest were also the ones that lost the least weight while consuming fewer calories, suggesting that fasting may be beneficial for some individuals but not others.

Further research is needed to investigate whether restrictive diets, such as intermittent fasting or calorie restriction, can extend human lifespan. The findings could also have implications for the way diet studies are conducted on humans.

According to Professor Gary Churchill of The Jackson Laboratory in the US, "Our study really points to the importance of resilience."

He added, "The most robust animals keep their weight on even in the face of stress and caloric restriction, and they are the ones that live the longest."

"It also suggests that a more moderate level of calorie restriction might be the way to balance long-term health and lifespan."

This was revealed in a study where researchers examined the effects of intermittent fasting and calorie restriction on nearly 1,000 female mice. The scientists explained that each mouse was chosen for its genetic uniqueness, which "allowed the team to better represent the genetic diversity of the human population" and made the research "one of the most significant investigations into ageing and lifespan to date".

The mice were randomly assigned to one of five different diets. The first group could eat any food at any time, while the second and third groups were given only 60% or 80% of their usual calories each day.

In the last two groups, the mice were starved for either one or two consecutive days each week but could eat as much as they wanted on the other days. The creatures were studied for the rest of their lives with regular blood tests looking at health markers such as body weight, body fat percentages, blood sugar levels and body temperature.

The team discovered that mice on unrestricted diets lived for an average of 25 months, those on the intermittent fasting diets lived for an average of 28 months, those eating 80% of baseline lived for an average of 30 months, and those eating 60% of baseline lived for 34 months.

The study found that animals which lost the most weight were likely to have low energy, compromised immune and reproductive systems, and shorter lives. Mice that naturally maintained their body weight, body fat percentage and immune cell health during periods of low food intake were found to live the longest.

However, within each group, the researchers noted a wide range of lifespans. In the group where mice consumed the fewest calories, lifespans ranged from a few months to four and a half years.

Upon analysing this data, the researchers discovered that genetic factors had a far greater impact on lifespan than diet. This emphasises the major role genes play in how diets affect an individual's health trajectory, they said.

Prof Churchill stated: "If you want to live a long time, there are things you can control within your lifetime such as diet, but really what you want is a very old grandmother."

He added: "While caloric restriction is generally good for lifespan, our data show that losing weight on caloric restriction is actually bad for lifespan."

"So when we look at human trials of longevity drugs and see that people are losing weight and have better metabolic profiles, it turns out that might not be a good marker of their future lifespan at all."