Intermittent fasting plus calorie restriction could be the key to living longer, study in mice suggests
- In an experiment, mice that ate at night – when they are normally active – and consumed fewer calories lived 35 per cent longer than a control group
- The research suggests cutting calories has positive effects that are magnified when combined with intermittent fasting in time with the circadian clock
Not only what we eat, but also when we eat it could play a role in how long we live, new research on mice suggests.
The idea that reducing the amount of calories you eat can extend your lifespan has been around for a while. But recently, a team from the University of Texas Southwestern Medical Centre in Dallas, in the United States discovered that caloric restriction extended mice’s lifespans the most when the mice ate in accordance with their circadian clocks.
The circadian clock is an internal timekeeping device that make sure our cells are primed for food, sleep and activity.
The work of the team, which is led by neuroscience professors Joseph Takahashi and Carla Green, was published in the journal Science in May.
“It really cemented this idea that aligning your eating with your circadian rhythms is so important to overall health,” said Green.
Future studies could yield clues about how human eating habits factor into our lifespans, she said.
Takahashi and Green, who are married, have studied circadian rhythms for years. Takahashi, chairman of the neuroscience department at UT Southwestern, identified the first gene known to control circadian clocks in mammals in 1997.
Eight years ago, the couple pored over previous research on caloric restriction in mice, and discovered the mice in these experiments were being fed exclusively during the day, even though mice are nocturnal.
Further, the mice were only being fed three times a week.
This was so scientists didn’t have to go into work at odd hours to feed their mice, but it wasn’t a good representation of how mice would normally eat.
The two tested how important caloric restriction was to mice’s lifespans when the mice ate according to their normal daily rhythms.
Green and Takahashi set up their experiment with several different groups of mice. They varied what and when the mice could eat, using three different feeding factors.
The first was calorie number. In the researchers’ control group, the mice’s diet wasn’t calorie-restricted. The other five groups were fed 30 per cent fewer calories.
The second was circadian rhythm alignment: how the mice’s feeding schedule aligned with when they normally ate. Some mice ate only at night, others ate only during the day.
The third was fasting time. In the day and night groups, some of the mice were given their food spaced out over 12 hours. The other mice were given their day’s meal all at once, and binge-ate it in two hours.
They provided the first direct evidence that fasting is an essential component of caloric restriction
A final group of mice was given their food over 24 hours, with no fasting at all.
To avoid manually feeding groups of mice day and night, at all hours, every day, for the mice’s entire lives, the scientists created their own feeders, designed to dispense food pellets at a preprogrammed time.
Over the course of the study, the team measured how long all the mice lived, and looked at what genes were expressed in each mouse over time.
They found that the mice that ate fewer calories, but over a period of 24 hours – with no circadian rhythm alignment – lived only 10 per cent longer than the control mice.
The calorically restricted mice that ate at night over a 12-hour period lived 35 per cent longer than the control group.
“It’s the same amount of food, the same calories,” said researcher Victoria Acosta-Rodriguez, an author of the study. “It’s when the mice eat that could have a huge impact on how long they live. For me, this was crazy.”
Roman Kondratov, a professor of biology at Cleveland State University in the US, said the research provided compelling evidence for the role of fasting in extending lifespan.
“Reduction of … calories has positive effects, but in combination with fasting, it’s even better.”
The mice that lived longest in the study ate from 6pm to 6am. For humans, that would look like restricting eating to any 12-hour period while we’re awake during the day. Takahashi said there’s evidence it’s better to begin that interval earlier in the day instead of skipping breakfast.
Both Takahashi and Acosta-Rodriguez have begun applying the study’s results to their own eating habits.
“If these findings hold true in people, we might want to rethink whether we really want that midnight snack,” Takahashi said.
“In Argentina, I will have dinner at, like, 10pm,” Acosta-Rodriguez said. “Here, I’m trying to do it at 7pm, and after this, trying not to get calories. Kind of like shortening the feeding windows.”
Green and Takahashi’s research provides some answers as to how what and when we eat factors into how long we live.
Now the researchers are looking at a crucial follow-up question: Why? Figuring out exactly which clock-regulating molecules or genes in mice helped them live longer in this study could be the key to applying these findings to humans.
“It’s going to be really interesting to look at the exact mechanisms of what aspect of this is really the critical feature that promotes longevity and the health of these animals,” Green said.
