Certain diets are designed to help extend lifespan. Researchers have now shown in mice that a calorie-restricted diet combined with daily fasting intervals is actually associated with longer life, at least in rodents. Mice whose food was restricted lived an average of 10 percent longer than their peers, which could eat when and how much they wanted. If they only got their food at night, i.e. at their natural activity time, they even got 35 percent older.
Many people hope that dieting will not only result in a lower body weight, but also a longer and healthier life. In fact, there is scientific evidence that reducing calorie intake and only eating at certain times of the day can be beneficial to health. Even independently of a possible weight loss, such a diet could possibly prolong life, researchers suspect. However, it was still unclear which factors and mechanisms play a role in this.
Automated feeding
A team led by Victoria Acosta-Rodríguez from the University of Texas in Dallas has now tested on mice how different nutritional concepts affect lifespan. To do this, they divided over 200 mice into six groups: A control group was allowed to eat when and as much as they wanted. All other mice received 30 to 40 percent less food than the control group at different times, each of which remained constant over the mice’s lifetime. In order to precisely control food intake, all mice lived in individual cages and received their daily rations via automatic feeders.
One group received their entire food ration, nine feed pellets, at the beginning of the day, another at the beginning of the night. Since the mice ate immediately and consumed everything within two hours, these animals had a daily fasting period of around 22 hours. Two other groups received a food pellet every 90 minutes for 12 hours, either during the day or during the night. The last group received the nine feed pellets evenly distributed over 24 hours.
timing of food intake is important
The researchers observed the mice for a total of four years until they all died of natural causes. In addition to the lifespan, they also documented various metabolic factors, regularly weighed the body weight of the animals and recorded the times at which the mice ran in the running wheel, i.e. were physically active. “All groups maintained their natural activity pattern throughout their lives and were mainly active at night,” the researchers report. “However, the mice fed during the day showed comparatively more activity during the day. They therefore interrupted their resting phase, although they continued to show nocturnal behavior. This would have negative metabolic consequences.”
However, the mice fed during the day lived, on average, longer than their free-feeding controls, which ate 75 percent of their food at night. “The mice from the control group lived an average of 792 days, so just over two years,” the researchers say. “In the mice on the calorie-restricted diet, life increased by 10 to 35 percent, depending on the time of feeding.” Mice from the 24-hour group lived an average of 875 days, mice fed twelve or two hours during the day lived an average of 942 and 959 days, respectively. “In addition to calorie reduction, a daily fasting period of at least twelve hours has its own positive effects on longevity,” the researchers conclude.
Impact on gene regulation
The mice that received their reduced-calorie diet at night lived the longest. They lived an average of 1058 or 1068 days, depending on whether they were fed over 12 hours or all at once. There was no significant difference between the two feeding variants. “Thus, 12 hours of fasting seems to be enough to prolong the life of the mice,” the researchers conclude. In addition, their results show that it was health-promoting, at least in the mice, if food intake took place during the natural activity time.
But why does the timing of food intake affect lifespan? The weight and body fat percentage of the mice from all calorie-restricted groups were similar, so they cannot be alone conclusive. On the basis of analyzes of gene expression, however, the researchers found an additional influencing factor: Apparently, diet influences genes that are involved in the mice’s day-night rhythm. While inflammatory processes increased with age in mice fed a distributed diet, daily periods of fasting partially reversed these age-related genetic changes—most effectively when fasting occurred during natural rest periods. Applied to humans, this would mean that food is best consumed during the day. However, it is still unclear to what extent similar effects can actually be demonstrated in humans.
Source: Victoria Acosta-Rodríguez (University of Texas, Dallas) et al., Science, doi: 10.1126/science.abk0297