Eating less improves health and can extend your lifespan

For nearly a century, laboratory studies have consistently shown that eating less food or eating less frequently can extend an animal’s lifespan. However, scientists have struggled to understand why these restrictive diets have this effect and how best to implement them in humans. 

Now, in a long-awaited study published in the journal Nature, scientists at The Jackson Laboratory (JAX) and their collaborators tracked the health of nearly 1,000 mice on various diets to explore these questions further.

Eating less, aging, and lifespan

The study was designed so that each mouse was genetically unique, allowing the team to better represent the genetic diversity of the human population. This approach makes the results more clinically relevant and elevates the study to one of the most significant investigations into aging and lifespan to date.

The researchers concluded that consuming fewer calories had a greater impact on lifespan than periodic fasting. They found that very-low-calorie diets generally extended the mice’s lifespan regardless of their body fat or glucose levels – both typically seen as markers of metabolic health and aging. 

Surprisingly, the mice that lived the longest on restrictive diets were those that lost the least weight despite eating less. Animals that lost the most weight on these diets tended to have low energy, compromised immune and reproductive systems, and shorter lives.

Long-term health and lifespan

“Our study really points to the importance of resilience,” said Gary Churchill, a professor at JAX who led the study. “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.”

According to Professor Churchill, the research also suggests that a more moderate level of calorie restriction might be the way to balance long-term health and lifespan.

Comparing various diets

The experts assigned female mice to one of five different diets, including one in which the animals could freely eat any amount of food at any time.

For two of the diets, the animals were provided only 60% or 80% of their baseline calories each day.

For the remaining diets, the animals were not given any food for either one or two consecutive days each week but could eat as much as they wanted on the other days. 

Eating less equals longer life

The mice were then studied for the rest of their lives, undergoing periodic blood tests and extensive evaluations of their overall health.

On average, mice on unrestricted diets lived for 25 months; those on intermittent fasting diets lived for 28 months; mice eating 80% of baseline calories lived for 30 months; and those eating 60% of baseline calories lived for 34 months. 

Genetic factors and lifespan

However, within each group, the range of lifespans was wide – for example, mice eating the fewest calories had lifespans ranging from a few months to four and a half years.

When the researchers analyzed their data to explain this wide range, they found that genetic factors had a much greater impact on lifespan than diets.

This highlights how underlying genetic features, yet to be identified, play a major role in how these diets affect an individual’s health trajectory. 

Resilience and lifespan

Moreover, the researchers identified genetically encoded resilience as a critical factor in lifespan.

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 late in life, survived the longest.

“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,” Churchill said.

Aspects of healthy aging

The study also casts doubt on traditional ideas about why certain diets can extend life. For example, factors like weight, body fat percentages, blood glucose levels, and body temperature did not explain the link between cutting calories and living a longer life. 

Instead, the study found that immune system health and traits related to red blood cells were more clearly connected to lifespan. 

Importantly, these findings suggest that human studies of longevity – which often use metabolic measurements as markers for aging or youthfulness – may be overlooking more important aspects of healthy aging.

“While caloric restriction is generally good for lifespan, our data show that losing weight on caloric restriction is actually bad for lifespan,” explained Churchill.

“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.”

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