"We know that persons with obesity who lose weight experience improvements in quality of life, but it was not clear if similar benefits would occur in normal weight and mildly overweight people," said lead author Corby K. Martin of the Pennington Biomedical Research Center in Baton Rouge, Louisiana.
"Some researchers and clinicians have hypothesized that calorie restriction in normal weight people might negatively affect quality of life," Martin told Reuters Health by email. "However, we found that calorie restriction over two years and loss of about 10 percent of body weight improved quality of life among the normal weight and mildly overweight people enrolled in the study."
The researchers recruited 220 men and women with a body mass index between 22 and 28. Body mass index (BMI) is a measure of weight in relation to height. Under 25 is considered normal; higher is considered overweight. Someone with a BMI of 28, for example, might be 5 feet 6 inches tall and weigh 175 pounds.
The researchers divided the study participants into two groups. A larger group was directed to reduce calorie intake by 25 percent. A smaller group was allowed to continue to eat as much as they liked.
The calorie-restriction group received a manual-based curriculum and had all their food provided for the first 27 days of the two-year study.
By the end of the study, those in the calorie restriction group had lost an average of almost 17 pounds, compared to less than a pound for the comparison group.
The participants completed quality of life questionnaires before the study began, at year one and at year two.
At year one, the calorie restriction group reported better quality sleep than those in the comparison group. At year two, they reported better mood, more sexual drive and better general health, as reported in JAMA Internal Medicine.
In another study published in the same issue of the journal, researchers led by Rena R. Wing of the Warren Alpert Medical School of Brown University divided a similar group of healthy young adults in the normal to overweight range into three groups, testing interventions to reduce weight gain.
Over a three-year period, the group with large intermittent behavior changes, aimed at losing up to nine pounds initially, gained the least weight. Another group, told to decrease their calorie intake by 100 calories per day and increase their calorie expenditure by 100 calories per day, also had less weight gain over time than a comparison group.
"The findings in these studies are not necessarily surprising since we expect adults who are motivated and participating in lifestyle interventions that focus on healthy eating and physical activity to lose weight and/or maintain their weight," said Dr. Tannaz Moin of the David Geffen School of Medicine at the University of California, Los Angeles, who wrote a commentary accompanying the two studies.
"There is some controversy about the best approaches for individual patients (i.e., how much to reduce and for how long) and from which food groups individuals should reduce calories (i.e., nuts are high in calories but also associated with many health benefits)," Moin told Reuters Health by email.
People who reduce calorie intake should still balance their nutrient intake with adequate vegetables, fruits, protein, and grains to avoid malnutrition, Moin said.
"Calorie restriction and weight loss have a number of health benefits, such as reduced blood pressure," Martin said.
On average, people in the calorie restriction group cut their intake by about 12 percent over two years, he said.
"The diets used in our study aimed to reduce calorie intake but be rich in nutrients, and participants were given a daily vitamin and mineral supplement," he said. "People could experience negative effects of calorie restriction if their diet is not nutritious."
He pointed out that it's possible to lose too much weight. This study had safeguards in place to prevent that from happening.
People who wish to diet in order to lose weight should consult a doctor first, and diet under the direction of health care providers and professionals, such as a Registered Dietitian Nutritionist, Martin said.