Why caloric restriction has health benefits is still not completely clear, but it seems that eating less primes the body to convert food into cellular energy without producing a lot of reactive oxygen species: unstable molecules that damage cells, contributing to a wide range of health problems from cancer to Parkinson’s. A urine test confirmed that participants in the caloric restriction group had lower reactive oxygen species levels than those in the control group.
CALERIE™ isn’t done yet. Recently, the researchers invited all the participants to come back into the lab for a follow-up study to see whether the early changes they made to their lifestyles still have positive impacts on their health over a decade later. Surveys will also reveal whether participants continued to restrict their calories after the study ended, when they were left to their own devices. Das and her colleagues have completed the data collection for this phase of the project and are beginning to conduct the analysis.
“I think the follow-up was necessary simply because we found such wonderful results in the primary study, and it is important to understand what the longer-term impacts are,” she says.
Meanwhile, many adults can safely get the benefits of moderate caloric restriction on their own, without taking part in an intensive study. There are some exceptions, such as people over age 65, young children, pregnant people, those with a body mass index under 22, and anyone who has bone density loss or a specific disease that requires medication. These groups should consult with their doctor before reducing their calorie intake. But for an average person who’s relatively young and healthy, Das says it’s easy to get started on your own.
“There are online tools that you can use to calculate how many calories you’re currently eating per day. Use that, and then take off 20%, or even just 10%,” she says. A decadent chocolate chip cookie contains about 200 calories, so for someone who eats a 2,000-calorie diet (which is about what’s recommended for women), cutting 10% might be as simple as skipping a daily dessert. Sugary coffee drinks can also be surprisingly high in calories, so cutting some of these out can be another good starting point.
People can spread out the calorie cuts over the course of a week in whatever way works best for them. Some people prefer to restrict calories only two days of the week: a diet known as 5:2 intermittent fasting.
Whether it’s best to continue caloric restriction indefinitely or do it for a set period of time, like in the study, is an open question. Go with how you feel, Das says. If you start to drop into the underweight range, or you feel lightheaded or low energy, those could be signs it’s time to recalibrate and see what is heathy for you.
And keep in mind: “You don’t have to shoot for crazy numbers, like 30% or 40% restriction. Even 10% is very helpful,” Das says. The benefits are especially important as medical advances extend the human lifespan, she adds. Those extra years won’t be much fun if they’re not years spent in good health.