If you feed mice less food than they normally eat, they tend to live longer. This mostly consistent finding is the basis for a lot of tech bro “biohacks” about eating less food. But is it really healthy to under-eat?
Most of the work on calorie restriction, as it’s called, has been in rodents, with mixed results in monkeys. But now we have new data from a human study. Over 200 normal-weight adults were assigned to eat either their normal diet or 25% less food (for example, 1,500 calories for someone who burns 2,000). And the results did show some changes in one measure of “biological age” after two years of attempting to follow the diet.
I say attempting because the average calorie restriction was more like 12% than 25%. The researchers used two different blood tests for DNA methylation, which is supposed to decrease as you age. One of the tests found no difference between the calorie restrictors and the control group. The other test found no difference in the first year, but some small changes during the second year that suggest a slight slowing of aging.
Can it really be healthy to under-eat?
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Biohacker bros talk about longevity all the time, but their concern often seems to be rooted in fears about disability or sometimes appearance. It’s not that they want to live longer, it’s that they’re afraid of looking and feeling old. Likewise, the enthusiasm for caloric restriction feels misplaced to me as well. Remember when everybody realized that tech bros’ obsession with fasting looks a lot like plain old dieting, maybe trending toward eating disorders? If eating less can make you skinny and maybe not get old, wouldn’t that be cool?
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But there’s a pretty obvious problem with eating less to ostensibly make you healthier: Under-nourishing yourself is not necessarily healthy! Rodent studies often use a 40% calorie restriction (equivalent to 1,200 for a person who burns 2,000) and the recent human study was supposed to be much more tolerable at just 25%. Since people only managed about half of that, we’re looking at more like 1,750, which seems like a moderate weight-loss diet. Not too crazy.
But as we’ve discussed before, it’s not realistic to diet forever, is it? Your body will eventually get used to the reduced amount of food, but is that actually a good way to live? Personally, I enjoy being strong, and I eat a lot of food. That’s partly to fuel my workouts, and partly to give my body the raw materials it needs to build muscle. As I’ve gotten stronger, I’ve gotten bigger, and that makes me happy. So I’m trying not to speak too much from my own biases here, but I think it’s too soon to start restricting calories in the name of health
We don’t know the consequences of long-term calorie restriction in humans
Ultimately, the problem is that we don’t know whether restricting calories for your whole life will actually make you more spry in your golden years, or just skinny and miserable.
We all tend to lose muscle as we age, which in severe cases is a phenomenon called sarcopenia. When you have very little muscle, it’s harder for you to stay active, which can lead to health problems, which can result in you spending more time in bed, and so on. People with sarcopenia can have trouble living independently and taking care of themselves, and may be more at risk for falls and fractures.
If you improve your metabolic health at the expense of your physical durability, are you really setting yourself up for successful aging? Sports nutrition researcher Eric Trexler argues that if you want to enjoy the later years of your life, caloric restriction is probably not the way to achieve that.
Ultimately, if you want to pursue caloric restriction for longevity, you’re making a huge gamble based on very incomplete information. So far we know very little about the results in humans, beyond some small changes to things like blood markers in the short term. In rodents, where most of the research has been done, there are still tons of questions remaining. For example, some strains of rodents show little to no benefit from caloric restriction. Some studies have shown problems with bone loss and with delayed wound healing.
Are you really going to bet your entire lifestyle on studies with mixed results? What if you’re hungry? What if you have no energy? What if it sucks? Are you just going to keep it up another 50 years and hope you’re on the right track?
I’m not going to, anyway. I’ll keep eating normal amounts of food, and focus my longevity-related efforts on things like sleeping well and getting a healthy diet with protein, vegetables, and micronutrients. Exercising, not smoking, not drinking too much, and having a lively social life are already known to help us stay healthy as we get older. If we’re choosing biohacks for longevity, I’ll take those.