The researchers found that cutting around 300 calories a day for two years significantly improved already good levels of cholesterol, blood pressure, blood sugar and other biomarkers in healthy adults.
The researchers, led by William Kraus of Duke University School of Medicine, compared the biomarkers for metabolic syndrome between a group with a normal calorie diet and a group of 143 study participants who agreed to reduce their daily caloric intake. Their results showed that the reduced-calorie group lost an average of 16 pounds after they cut their daily intake by an average of about 12 percent or roughly 300 calories.
This randomized, controlled trial is part of an ongoing project with the National Institutes of Health called CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) that builds on the hypothesis that the individuals’ progress and improvements are not just triggered by weight loss, but by some other more complex metabolic change brought about by eating fewer calories than what is expended.
"There's something about caloric restriction, some mechanism we don't yet understand that results in these improvements," said Kraus, who is also a cardiologist and a professor of cardiovascular genomics.
"We have collected blood, muscle and other samples from these participants and will continue to explore what this metabolic signal or magic molecule might be," Kraus added.
The participants ate three meals a day that would cut one-fourth of their daily calories to help train them on the new diet. They chose from six different meal plans that accommodated preferences and other personal needs. In addition, the participants attended group and individual counseling sessions for the first six months of the trial, while the control group continued their usual diet and met with researchers once every six months.
After that initial six-month training period, the researchers then asked the participants to do their best to try and continue to eliminate a quarter of their daily calorie intake. (Related: Study in diet trends reveals that a poor diet is WORSE for your health than drinking and smoking.)
The researchers found that while most couldn't quite stick to the diet as strictly as they can for two years, the average participant was still able to eat about 12 percent less.
As detailed in the Lancet article, the researchers found that this relatively mild diet allowed the participants to shed – and actually keep off – an average of 10 percent of their weight, 71 percent of which was pure fat.
In addition to monitoring their subjects’ eating habits, the researchers regularly collected blood and fat samples from the participants, which they checked for biomarkers related to metabolic syndrome, such as insulin resistance, glucose tolerance, high blood pressure, high triglycerides and high cholesterol.
They found that two years of calorie restrictions led to reductions in the participants’ risks for heart diseases, cancer and cognitive decline.
"There's something about caloric restriction, some mechanism we don't yet understand that results in these improvements," Kraus said, noting that their discovery may help reduce the burden of diabetes and cardiovascular disease that we have in the United States.
"This shows that even a modification that is not as severe as what we used in this study could reduce the burden of diabetes and cardiovascular disease that we have in this country," Kraus said.
"People can do this fairly easily by simply watching their little indiscretions here and there, or maybe reducing the amount of them, like not snacking after dinner."
These findings suggest that practicing moderate calorie restriction in young and middle-aged healthy individuals has the potential to substantially improve their cardiovascular health, adding that their findings "offer promise for pronounced long-term population health benefits."
According to Kraus, while he and his team still aren't sure what it is about calorie restriction that has these beneficial effects, they will be keeping the samples from the study participants on deck for further studies.