Eating far less will make you live longer
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Sort of. Eating far less lengthens life in mice and many other animals. The two big monkey studies split, one finding longer lives and one not. In people, a 2-year trial in which adults ate about 12% less improved blood pressure, cholesterol and one measure of how fast they were aging. Nobody has measured whether it adds years to a human life.
What we’d do
Don’t starve yourself for longevity. If you carry a lot of extra weight, losing some is one of the habits with years attached. If you’re already at a healthy weight, eat enough protein to keep your muscle and put the effort into fitness and strength instead. Hard calorie cuts cost muscle, and muscle is what keeps you independent later.
If you remember three things
- In mice, yes. In 960 genetically diverse mice, the more they were restricted, the longer they lived, though their genes made a bigger difference than the diet.
- In monkeys, it depends on the study. One found 80% of restricted monkeys alive against 50% of the others. The other found no difference in survival.
- In people, only markers so far. Two years of eating about 12% less took off 16.5 pounds (7.5 kg) and slowed one aging clock by 2 to 3%.
Why everyone believes it
Because in the lab it’s one of the most reliable results there is. Feed mice and many other animals less, without starving them of nutrients, and they tend to live longer. Fasting diets are popular for weight loss, and longevity sounds like a bonus on top. If eating less works in mice, it seems only a matter of time before it’s shown in people.
A picture from daily life
Think of driving a car only in low gear to make the engine last. It may well last longer. But if you never shift up, you can’t get up the hills, and some of what you saved goes on the struggle. The restricted mice lived longer, and the strictest diet also cost them muscle and changed their immune cells.
What happened in mice?
In 2024 researchers put 960 genetically diverse female mice on 20% or 40% calorie restriction, or on one or two days a week of fasting. Both restriction and fasting lengthened their lives, more with more restriction. But genes made a bigger difference to how long each mouse lived than the diet did. The 40% diet worked best for lifespan, and it cost the mice lean mass and changed their immune cells in ways that could leave them open to infection. Fasting didn’t lengthen the lives of mice that started out heavy. And the changes that looked healthiest, less fat and lower blood sugar, didn’t predict which mice lived longer.
What happened in monkeys?
In the late 1980s two teams started feeding rhesus monkeys about 30% less, one at the University of Wisconsin and one at the National Institute on Aging. In 2009 the Wisconsin team reported that at the point they checked, 80% of the restricted monkeys were alive against 50% of the others, with less diabetes, cancer, heart disease and brain shrinkage. In 2012 the NIA team reported that their restricted monkeys hadn’t lived any longer.
In 2017 the two teams pooled their data. The diets were different. Sugar made up 45% of the carbohydrate in the Wisconsin monkeys’ food and under 7% at the NIA. And the NIA’s comparison monkeys weren’t free to eat as much as they liked, so they may have eaten less than truly free-fed monkeys would. The teams concluded that the health benefits of eating less hold in monkeys, and that design choices like these could explain the split.
What happened in people?
Two years of eating less
218 healthy adults aged 21 to 50, not obese. Kraus, Lancet Diabetes and Endocrinology, 2019
Asked to cut 25%, people managed 11.9%, from 2,467 to 2,170 calories a day. They lost 16.5 pounds (7.5 kg), 71% of it fat, and their blood pressure, cholesterol and other heart risk markers improved.
It measured markers over two years. Nobody has measured years lived.
The aging clocks
The same trial, blood samples. Waziry, Nature Aging, 2023
One DNA clock, DunedinPACE, showed the pace of aging 2 to 3% slower. Two others, PhenoAge and GrimAge, showed no change.
The authors called the effects small, and the clocks disagreed.
Thinner isn’t always better in the long run either. In the Harvard study of 123,219 health professionals, people with a BMI of 18.5 to 22.9 had a slightly higher death rate (6%) than people at 23 to 24.9. Risk only climbed steeply over 30.
Isn’t it the most proven life extender in biology?
The sceptic says
Calorie restriction works in almost every animal tested. The monkeys mostly agree once the studies are compared, and people’s markers move the right way. It would be strange if humans were the exception.
The reply
It might well work in people, to some degree. But nobody has kept people on it long enough to know, it’s very hard to keep up (the trial’s volunteers managed half of what they were asked), and it costs lean mass. Even in mice, genes mattered more than the diet. Fitness and strength have years-lived results in people already, so we’d start there.
7 sources
- Di Francesco A and others, Dietary restriction impacts health and lifespan of genetically diverse mice, Nature, 2024pmc.ncbi.nlm.nih.gov
- Colman RJ and others, Caloric restriction delays disease onset and mortality in rhesus monkeys, Science, 2009pmc.ncbi.nlm.nih.gov
- Mattison JA and others, Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study, Nature, 2012pmc.ncbi.nlm.nih.gov
- Mattison JA and others, Caloric restriction improves health and survival of rhesus monkeys, Nature Communications, 2017pmc.ncbi.nlm.nih.gov
- Kraus WE and others, 2 years of calorie restriction and cardiometabolic risk (CALERIE): exploratory outcomes of a multicentre, phase 2, randomised controlled trial, Lancet Diabetes and Endocrinology, 2019pmc.ncbi.nlm.nih.gov
- Waziry R and others, Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial, Nature Aging, 2023pmc.ncbi.nlm.nih.gov
- Li Y and others, Impact of Healthy Lifestyle Factors on Life Expectancies in the US Population, Circulation, 2018pmc.ncbi.nlm.nih.gov
