Caloric Restriction: The Science of Eating Less and Living Longer

Research suggests consuming fewer calories could slow the aging process, but could it really work?

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Imagine being able to push back the clock a few years. You come off your accumulated meds, your side effects melt away. You feel healthier, look better, and have tons more energy -- in short, you have grown young.

It’s a seductive notion, and there’s research that suggests it might be possible. The science of “caloric restriction” -- a branch of nutrition research devoted to seeing whether simply cutting calories interferes with the normal biological programming of aging to an extent that we can actually stop the clock, in biological terms – is gaining traction and, unsurprisingly, no small amount of interest.

Caloric restriction as a research discipline has actually been around for ages. The first demonstration of extending lifespan and improving health in rats by cutting calories was back in 1934, and since then the finding has been repeated in numerous species up to and including non-human primates. Animals subjected to caloric restriction while maintaining adequate vitamin, mineral, and protein intakes not only live longer, healthier lives, they also maintain vitality to an older age and have fewer visible signs of aging – such as white fur – compared to better-fed siblings.

It is worth noting that we are not just talking about shedding a few pounds here. Animal studies show that, almost up to the point of frank starvation, the more calorie restriction the better when it comes to extending lifespan and health. Humans who live by the theory typically have a BMI of between 18 and 21 -- very thin by any world standard. Which raises an important point: caloric restriction that drifts into eating-disorder territory is a real concern and definitely to be avoided. Anorexia will in no way lengthen your life (quite the opposite, in fact) so it's crucial to make sure you're always eating enough of the right foods to get all the necessary fiber, protein, and vitamins.

But does it even work in humans? Right now we can’t say. For sure, sustained weight loss is healthy and even energizing if you are overweight or obese to begin with, but that’s different from caloric restriction in the scientific sense, which is all about cutting calories beyond what’s needed to maintain a weight judged to be healthy by regular standards. The NIH has sponsored the first long-term randomized controlled trial of human caloric restriction and “metabolic aging,” which is in its final stages, but this major trial is probably still 18 months from official publication. In the meantime, the fact that caloric restriction may help people grow young and transform lives makes it hard to ignore every new animal study and tantalizing short-term human pilot project that comes along.

One recent pilot study from a group at Ohio University examined whether intermittent caloric restriction may be as healthful as a continuous regimen. Ten mice (yes, that is the weakness of this study so far: just 10 mice, but the senior scientist told me he is working on enlarging the group) were assigned to intermittent caloric restriction, induced by alternating all-you-can-eat quantities of high-fat or low-fat diets (an interesting experimental design in its own right!) These mice were found to live longer than 10 other mice that were continuously fed the high-fat diet, and about the same length of time as 10 mice fed the low-fat diet. So yes, it did seem to work to the extent it was tested.

Of course, mice are not people, and unfortunately we don’t yet have many studies that can help us find the bottom line for humans. One 2005 study of alternate-day fasting in 16 adult men and women reported weight loss and decreased circulating insulin (a predictor of longevity in humans), but also reported widespread unpleasant side effects including constipation, lightheadedness, irritability, and hunger. This makes complete sense to me. If I spent my days alternately fasting and eating whatever I like, I’m sure the fasting days would be harder because the huge meal I ate the day before would still be fresh in my mind.

Virtually every animal study ever done on caloric restriction has shown benefits for health and longevity, and now we have emerging studies showing that even intermittent caloric restriction may be beneficial, so it would be almost surprising if humans turned out to be the only species to have a negative response. Unlike research animals, however, humans don’t live alone in pre-paid houses with the right kind of food carefully provided by scientists, so if caloric restriction is to be a feasible strategy for maintaining health as we age it has to be feasible to implement – in other words, doable and practical in real lives in the real world. In practice, that means keeping hunger down to manageable levels despite cutting calories, and eating in ways that allow us to maintain our cheerfulness and resiliency in the face of everyday challenges.

Right now, there are no human research studies that give us a good road map for how to achieve that, but hopefully the upcoming NIH trial will provide valuable information. In the meantime, people who are impatient to start and want to get going on their own can look to the success stories -- formerly obese dieters -- and tank up on fiber, protein, and high-volume foods like legumes, lean proteins, high-fiber cereals, and veggies. That is not only a pretty easy way to cut calories, it’s also a shortcut to healthy metrics like decreased blood pressure, cholesterol, and blood glucose, irrespective of caloric restriction.

A famous gerontologist of my acquaintance once told me that he was convinced that old age begins at 42. One of the reasons I’m personally in love with the promise of caloric restriction is that I’ve already passed that point of no return. Yet I’m a long way from being ready to feel old. But let’s keep watching for what the human caloric restriction trials show before we adopt intermittent fasting as the latest fad, and in the meantime, use the proven methods to maintain health and vitality.