Diets, whether calorie restriction or intermittent fasting, can positively influence the longevitybut a new study in mice suggests that genetics may play a larger role in determining lifespan.
Research led by the Jackson Laboratory (USA) and published in Nature analyzed the complex relationship between dietary restriction and longevity across 960 genetically diverse female mice, representing a wide range of physiological characteristics.
For almost a century, laboratory studies have shown consistent results that if an animal eats less or less frequently, it will live longer. However, scientists have struggled to understand why these types of restrictive diets lengthen life and how to best apply them to humans.
Mice were randomly assigned to one of five diets: unlimited food access, fasting one day per week, fasting two consecutive days per week, and caloric restriction to 20% or 40% of basal food intake.
They were then studied for the rest of their lives with regular blood tests and a thorough evaluation of their general health.
All dietary restrictions prolonged the life of the rodents, with responses proportional to the degree of restriction, but only calorie restriction significantly reduced the rate of aging.
In addition, it prolonged lifespan to the same extent in the lightest and heaviest mice, while those subjected to intermittent fasting with a high body weight before the intervention showed no signs of prolonged lifespan.
The study concluded that eating fewer calories had a greater impact on life expectancy than periodic fasting, revealing that very low-calorie diets generally prolonged the life expectancy of mice, regardless of their body fat levels or glucose, both commonly considered markers of metabolic health and aging.
In general, Mice on unrestricted diets lived an average of 25 months; those who followed intermittent fasting diets for 28 months; those who ate 80% of the usual 30 months and those who ate 60% lived 34 months.
Dietary restriction was observed to improve metabolic traits of the mice, including fasting blood glucose, but the metabolic improvements were not directly associated with prolonged lifespan.
Surprisingly, the mice that lived the longest on the restrictive diets lost the least weight despite eating less, while the animals that lost the most weight tended to have low energy, compromised immune and reproductive systems, and shorter lifespans.
But within each group, life expectancy was very long; Mice that ate fewer calories, for example, had life expectancy ranging from a few months to four and a half years.
Genetic background has more influence
The researchers analyzed the rest of the data to try to explain this wide range and found that genetic factors had a much greater impact on life expectancy than diets.
Despite the multiple effects of dietary restriction, The authors concluded that genetic background influences life expectancy more than dietary interventions.
This highlights how underlying genetic characteristics, yet to be identified, play an important role in how these diets would affect the health trajectory of an individual person, the Jackson Laboratory said in a statement.
Furthermore, they pointed out genetically encoded resilience as a critical factor in life expectancy.
Mice that naturally maintained their body weight, body fat percentage, and immune cell health during periods of stress or low food intake, as well as those that did not lose body fat at the end of their lives, were the ones that survived longer.
“If you want to live a long time, there are things you can control throughout your life, like diet, but what you really want is a very old grandmother.”said Gary Churchill, who led the study.
The results suggest that the metabolic benefits induced by dietary restriction may not necessarily translate into longevity in mice, so it is necessary to further investigate whether intermittent fasting and caloric restriction would prolong lifespan in humans.