With that in mind, if you knew that you could help keep your heart healthy by eating just a little bit less every day — about six standard-size Oreos' worth of calories — would you?
Researchers have found evidence that just a modest reduction in our daily caloric intake could have protective benefits for our hearts, according to a paper published this week in The Lancet Diabetes & Endocrinology.
The paper drew on data from the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) study. That landmark project, supported by the National Institutes of Health, was one of the most in-depth efforts to measure the long-term impacts of caloric restriction in humans. Researchers have published numerous analyses drawing on data from the two-year study, examining various factors associated with life expectancy and longevity.
This paper, the latest to draw from the data, primarily examines how moderate caloric restriction impacts heart health and how it may potentially prevent aging-related decline.
The experiment began with 218 participants, all of whom were normal weight or just slightly overweight and between ages 21 and 50. Researchers started 143 participants on a diet that reduced their caloric intake by 25%; 75 others were assigned to a normal diet. In the end, 188 participants completed the study — 117 with caloric restriction and 71 without.
For the first four weeks of the study, people in the calorie-cutting group were fed in-house at one of three clinical centers. During this time, they were instructed on how to reduce their caloric intake and gradually fell into one of six eating plans based on their own preferences.
Over the first six months, most people stuck pretty well to their diets. On average, they cut back on calories by about 20%. But they didn't fare as well over two years: Overall, they trimmed their caloric intake by an average of about 12% — or about 300 fewer calories per person per day.
Even so, this relatively modest reduction in calories had significant effects on the participants who ate less: They lost about 16.5 pounds on average and saw improvements, including lowered cholesterol and blood pressure, on all six primary factors associated with risks to heart health. They also saw improved insulin resistance and metabolic rates.
"We expected there to be [some] improvement on cardiometabolic factors because of weight loss," says William Kraus, the study's lead author and a distinguished professor of cardiovascular genomics at Duke University. "But ... we didn't expect the degree of improvement we saw."
And though the weight loss was relatively impressive, it wasn't responsible for a majority of the heart benefits. After conducting further analysis, researchers determined that at most, weight loss accounted for only 25% of the improved measurements in heart health. The researchers say their findings suggest that caloric restriction can have health benefits above and beyond those normally associated with weight loss.
David Sinclair, a professor of genetics at Harvard Medical School, says the findings provide further evidence that caloric restriction can be beneficial to staving off the negative effects of aging.
But, he says, the study also demonstrates a significant problem with using caloric restriction to improve human health: It's really hard to maintain, even for motivated people. Of the 143 participants who originally began the restricted diet, 26 dropped out before the two years were up. (Small sample size was a limitation of the study.) Many others were screened out from the initial study pool because of concerns about their physical or mental health.
"You can't expect the elderly or frail to do this severe dietary regimen," says Sinclair, who was not involved in the study. "We need alternatives, be they intermittent fasting or medicines that mimic calorie restriction." He is working to understand how caloric restriction works on a molecular level so that he and others can come up with medications that confer the same benefits without the pain and difficulty.
The goal of any caloric restriction research, he says, is the reduction — and maybe elimination — of aging-related diseases.
"Aging isn't considered a medical condition — it's just too common. Hopefully, in the near future, we won't accept it," he says. "That's what calorie restriction offers: It compresses the period of sickness. People one day will hopefully live into their 90s in a healthy way and pass away more quickly and [less] painfully than we do now."
Susie Neilson is an intern on NPR's Science Desk. Follow her on Twitter: @susieneilson.