If you’ve ever tried to lose weight (and most of us have), you’re familiar with calorie restriction (CR) or eating less than you usually do to shed extra pounds. Over the last 90 years, scientists have investigated CR for another purpose: to see if it slows aging and adds extra years to the average life span.
In fact, a scientific paper that was published in the Journal of Nutrition goes so far as to say that—because aging is the leading risk factor for chronic diseases and disability—CR for slower aging is “the most important health intervention that has ever been studied.”
CR in the lab
The first research on CR and aging was published in 1935 by Clive McCay, PhD, a professor at Cornell University. He found that feeding rats a calorie-restricted diet with adequate vitamins and minerals nearly doubled their life span.
Since then, there have been similar findings in fruit flies, worms, rodents, and nonhuman primates like rhesus monkeys—with most research showing significant increases in life span.
CR doesn’t just support longer life in animal models: It also supports healthier life as an organism ages. A phenomenon called “health span” describes freedom from the chronic diseases and disability of aging, no matter how long a person lives. In addition, research on nonhumans shows that the benefits of CR don’t depend on a lifetime of calorie restriction. CR could benefit an organism at any age—even when the dietary regimen was started in midlife.
But fruit flies and worms aren’t people. Would calorie restriction have the same effects in us humans?
CR in humans
To find out, scientists conducted so-called “observational” studies on people who had chosen CR as a lifestyle (such as members of the Calorie Restriction Society). Investigators found very low levels of cholesterol and triglycerides, very low blood pressure, levels of inflammation 20 times lower than normal, and hearts that resembled those of people 17 years younger.
But there had never been a rigorous study of the effects of calorie restriction in people who weren’t obese until the CALERIE Trials, the largest and most systematic examinations of prolonged CR in nonobese people. The most recent study was CALERIE 2. This two-year study involved 220 people: 145 who participated in CR and 75 who were eating a normal diet. The participants were 21 to 50 years old, healthy, and of normal weight. The study aimed to cut calories by 25 percent in the participants’ diets, but participants averaged a reduction of 11.9 percent. That’s a reduction of about 300 calories a day in the recommended calorie intake for an adult man (2,500 calories) and a reduction of about 240 calories in the recommended intake for an adult woman (2,000 calories).
Even with an 11.9 percent reduction, the benefits were remarkable.
Many benefits of CR
In a recent issue of the journal Nutrition Reviews, a team of CALERIE 2 researchers summarized the many benefits of an 11.9 percent calorie restriction.
- Weight loss. Although they weren’t overweight, people in the CR group lost an average of 10 percent of their body weight. They lost body fat generally and abdominal fat in particular. Reductions in abdominal fat are linked to a lower risk of heart disease and type 2 diabetes.
- Less oxidation. The CR group participants had lower levels of several key markers of oxidation, a kind of cell- and tissue-destroying inner rust that is linked to chronic disease.
- Slower aging. The researchers used two algorithms to estimate the rate of biological aging or deterioration of tissues and body systems and found that the control group was aging nearly seven times faster than the CR group.
- Less inflammation. Low-level, chronic inflammation is linked to many chronic diseases, and the CR group had a 40 to 50 percent average reduction in two biomarkers of inflammation.
- Lower insulin resistance. Insulin is the hormone that ushers glucose (blood sugar) out of the bloodstream and into the cells. Insulin resistance—where the hormone’s action is blocked—is linked to increased risk for type 2 diabetes, cardiovascular disease, cancer, and a shorter life. The CR group had a 20 to 30 percent reduction in
- Better blood fats. After 24 months, the CR group had lower “bad” LDL cholesterol and higher “good” HDL cholesterol, while the control group had no changes. The CR group also had lower levels of triglycerides, another heart-hurting blood fat.
- Lower blood pressure. The CR group had a significant drop of both diastolic (upper reading) and systolic (lower reading) blood pressure.
- Healthier livers. The CR group had improvement in several biomarkers of liver health.
- Improved immunity. The thymus gland generates the T-cells that help fight off infectious microbes, like viruses and bacteria. After two years, the CR group had healthier glands with less fat and more volume.
- Improved mood. The CR group had improvements in mood, tension, and anxiety, compared with the control group.
- Better memory. The CR group had greater improvements in working memory—the ability to work with information without losing track of what you’re doing.
- More regulated eating. The CR group had a better ability to regulate food intake, particularly in social settings and during physical discomfort.
- Higher sex drive, better relationships. The CR group had a small improvement in sex drive and the quality of their relationships, compared with the control group.
Implementing CR is a two-step process: 1) figuring out how many calories you eat on average; 2) cutting calories.
Determine daily calories. There are many apps for both Android and iPhone that help you determine your current calorie count, such as MyFitnessPal, Lose It, FatSecret, Cronometer, and Noom. MyFitnessPal, for example, has a database that includes 5 million foods, including many restaurant foods. Track your calories for seven days to create a daily average. Now you’re ready to reduce calories by around 12 percent.
Reduce daily calories. In CALERIE 2, the researchers found that reducing calories was very individualized, with different dietary strategies working for different people. (See the sidebar for some suggestions.) Once you’ve put your strategies in place, continue to track your daily calories so you’re sure they’re reduced by approximately