Mountains of evidence show that people who are obese can benefit from eating less and losing weight. Now, research suggests that even healthy, nonobese individuals may reduce their risk for chronic health conditions, including type 2 diabetes and heart disease, simply by cutting 300 calories per day.
The two-year study, published in July 2019 in the journal The Lancet Diabetes & Endocrinology, found that people younger than 50 who had normal weight or were overweight, and had healthy levels of cholesterol, blood pressure, and blood sugar could get healthier with moderate calorie reduction. Roughly six cookies, 30 potato chips, or a 2/3-cup serving of vanilla ice cream is just over 300 calories, depending on the product.
Study participants lost an average of 16 pounds over the course of the study, but a detailed analysis revealed only about 25 percent of the benefits were tied directly to weight loss, says lead author William E. Kraus, MD, a cardiologist and professor of cardiovascular genomics at Duke University School of Medicine in Durham, North Carolina. “Our results suggest that there is something about caloric restriction itself that improves health,” says Dr. Kraus.
Frank Hu, MD, PhD, professor and chair of the department of nutrition at Harvard T.H. Chan School of Public Health in Boston, says the study is novel. “The findings are important because it is the first long-term calorie restriction intervention in healthy nonobese individuals to demonstrate that modest calorie restriction significantly improves cardiometabolic risk factors,” he explains. Dr. Hu wrote an editorial that accompanied the study but was not involved in the research.
Could Eating Less Be the Best Medicine?
Researchers randomly assigned participants to the calorie restriction group or a control group that had no restrictions on their food intake. The calorie restriction group consisted of 143 people (44 men and 99 women), while the control group consisted of 75 people (22 men and 53 women).
The study population was 76 percent white, 15 percent African American, and 9 percent Asian, Native American, or Pacific Islander, with an average age of 38. The participants’ average baseline body mass index (BMI) was 25.1, which would place participants in the normal and overweight weight range, per the National Heart, Lung, and Blood Institute.
Researchers selected a younger, mostly normal-weight population for a few key reasons, says Kraus. “We designed this study on the basis of the results we’ve seen in animals trials where calories have been restricted,” says Kraus. In most cases, the earlier you start the calorie restriction, the greater its effects on life span and health span, he says. Health span is the period between the start of the intervention and the start of the disease, says Kraus. Kraus and his team also wanted to see what benefits, if any, calorie restriction could have for people who weren’t overweight.
For the first month of the study, subjects ate three meals per day designed to cut 25 percent of their daily calories and get them familiar with their new normal.
After one month, participants were able to choose from a variety of eating plans that researchers modified to suit different cultural preferences. In addition to receiving coaching on the basics of calorie restriction, participants attended group and individual counseling sessions for the first six months of the trial.
Maintaining a 25 percent calorie reduction proved challenging despite the support participants received. The majority fell short of the goal, with participants cutting, on average, only 12 percent of their calories by the end of the trial.
Despite not meeting researchers’ goal, the participants in the restriction group tended to eat less fat than the control group, says Susan B. Roberts, PhD, senior scientist of the U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University in Boston, and principal investigator for the study. “At the same time, they had big increases in vitamin K and magnesium intakes, which are markers of a generally healthy diet, including such foods as green vegetables, whole grains, and legumes,” like beans, lentils, edamame, and chickpeas, Dr. Roberts says.
After two years, the calorie restriction group specifically saw many health improvements, including:
- A significant decrease in total cholesterol and LDL “bad” cholesterol
- A 24 percent drop in serum triglycerides concentrations, a type of fat in the blood, as well as improved insulin sensitivity (which reduces the risk for type 2 diabetes)
- A significant reduction in systolic, diastolic, and mean blood pressure (though baseline blood pressure values were normal for participants at the start of the trial)
- A major reduction in the metabolic syndrome score, which factors in waist circumference, systolic blood pressure, levels of HDL “good” cholesterol, triglycerides, and blood glucose to determine certain risks, such as heart disease
- A reduction in a biomarker that indicates chronic inflammation and has been linked to heart disease, cancer, and cognitive decline
“These results show that a modification in calories could reduce the burden of diabetes and cardiovascular disease that we have in this country,” says Kraus. It would be hard to find a combination of medicines that would lead to the sorts of reductions achieved in the calorie restriction group, he adds.
Although the calorie cutting participants lost about 10 percent of their body weight, that wasn’t the driver of these results, says Kraus. “There’s something about caloric restriction, some mechanism we don’t yet understand, that results in these improvements,” says Kraus.
Whether these findings could have real-world application is unclear, says Hu. Although participants in the study were highly motivated and the intervention was intensive, many people couldn’t comply with the goals of the study, says Hu. “The average reduction in energy intake over two years was about 12 percent in the calorie restriction group, much less than the targeted 25 percent calorie restriction,” he says.
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Calorie Restriction: The New Fountain of Youth?
There could also be implications for what calorie restriction interventions could do for long-term health and postponing death, even for people who try it for a defined period rather than a lifetime, says Kraus.
Although this was not proven or part of this study, Kraus and colleagues theorize that calorie restriction, even in young people at a normal weight, could help “reset the baseline,” or postpone how long it will take for people to develop potentially life-ending diseases.
“Let’s say in the current environment where it’s common for individuals to overeat, a person might develop diabetes over the course of 20 years,” says Kraus. Then take a scenario where that person does a calorie restriction intervention where they reset their baseline and begin again with a lower risk. This could potentially result in diabetes taking 25 years rather than 20 to develop, he says.
The Diabetes Prevention Program (DPP) shows this, says Kraus, referencing a large study that looked at the benefits of lifestyle changes and continues to track participants. The people in the arm of that study that practiced diet and exercise changes lost 7 percent of their body weight over six months, says Kraus. People in that arm managed diabetes better than the metformin group or the control group, he says. (Metformin is a common drug prescribed to lower blood sugar in people with type 2 diabetes.)
A follow-up study published in the The New England Journal of Medicine looked at the DPP subjects 10 years later. It found that no matter which diet or exercise plan the subjects followed (or didn’t follow) during those years after the study, the people who had been in the diet and exercise group were still managing their condition better than the metformin or control groups, says Kraus.
The six months of lifestyle intervention they got in the study reset the baseline and resulted in an improvement that was persistent, called a legacy effect, says Kraus. “This could be what we eventually find out in our calorie restricted group,” he says. “We could be resetting the baseline in normal people so it will be longer until they get certain diseases,” he says, adding that research has yet to prove this notion is true.
It could be that person doesn’t necessarily need to sign up for a lifetime of calorie deprivation to get lifelong benefits, says Kraus. A person could potentially reset their baseline to lasting effect by doing it for a defined period, like the six months in the DPP or the two years in this study, he adds.
One step in determining that would be to bring the people in this study back in 10 years to see if they actually had a legacy effect, says Kraus. “We’d compare the groups and assess,” he says. “Are the two arms still different even if they haven’t been counting calories, and did the restrictive group keep up any of the habits they adopted in the study?” he says.
Other next steps for research would be to combine caloric restriction with other lifestyle interventions, such as modest physical activity, and track the changes, says Kraus.
It would be interesting to compare the continuous calorie restriction used in this study with other methods, such as intermittent fasting, to see how that might improve cardiometabolic risk factors, says Hu.
A Simple Way to Try to Restrict Calories
It might sound daunting to cut out 300 calories a day, but it doesn’t need to involve lots of calorie counting, says Kraus. “The easiest way to do it is no eating after dinner,” he says. “That’s where most of the unnecessary calories come from and where you can make an impact without too much pain,” he adds.