Calorie restriction is a type of diet that reduces calories without impacting nutrition. It can be achieved by eating less overall. Previous research has shown possible health benefits from long-term calorie restriction. Animal studies suggest that calorie restriction can delay the progression of a number of age-related diseases.
Dr. William E. Kraus of Duke University led a team of researchers to investigate the health effects of calorie restriction in young and middle-aged adults who were not obese. The two-year trial was supported by NIH’s National Institute on Aging (NIA) and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
The investigators randomly assigned 218 adults to either calorie restriction or their usual eating pattern. At the beginning of the study, the men and women were healthy and either normal weight or slightly overweight. Those in the calorie restriction group were given coaching over the course of the trial to help them try to achieve and sustain a 25% reduction in their daily caloric intake.
The researchers tracked energy intake and expenditure. On average, the 143 adults in the calorie restriction group maintained nearly 12% calorie restriction over the entire two-year period. This group also achieved an average reduction of 10% in body weight, mostly body fat. The 75 adults in the control group had stable calorie intake and weight during the study.
The team published a report in 2015 on the primary outcomes of the study, which were chosen to test whether calorie restriction would affect metabolism. They found that calorie restriction didn’t affect body temperature. It lowered the resting metabolic rate for a time, but the difference wasn’t significant at the end of two years.
In their new report, the researchers detailed outcomes related to risk factors for heart disease and diabetes. The findings were published on July 11, 2019, in Lancet Diabetes and Endocrinology.
Compared to the control group, calorie restriction substantially reduced waist measurements and blood pressure. Lab tests showed reduced LDL cholesterol and triglycerides. In addition, measures of inflammation, insulin resistance, glucose control, and metabolic syndrome greatly improved.
The findings suggest that modest calorie restriction may reduce the risk of heart disease and diabetes even in healthy adults who are not obese. “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,” Kraus says.
More research is needed to understand how calorie restriction results in these benefits. The long-term impact of calorie restriction in healthy adults of normal weight also needs further study.