A well-planned diet and regular exercise do help overweight, obese and severely obese people lose weight, two research studies have claimed.
The studies, published in Wednesday's print edition of the Journal of the American Medical Association, show that behavioral changes can have a significant impact, in contrast to increasingly popular surgical interventions, such as gastric bypass procedures.
Both studies used pre-packaged meals as part of their evaluations, and offered financial incentives to those participating.
One study used Jenny Craig weight loss products. Led by Cheryl Rock of the Moores Cancer Center in California and funded by Jenny Craig, researchers conducted a two-year trial of weight loss and maintenance among 442 overweight or obese women aged 18 to 69.
Their Body Mass Index -- a measure of body fat based on height and weight -- was 25 or higher. Normal BMI ranges are typically 18.5-24.9.
The subjects received in-person or telephone counseling as well as free, prepackaged foods and instructions for increased physical activity for 30 minutes a day, five days a week.
After two years, the average weight loss for women in the center-based group was about 16 pounds (seven kilograms) or 7.9 percent of their initial weight.
The telephone-based group lost about 14 pounds (six kilograms) or 6.8 percent of their body weight.
Women in a control group received two individualized weight loss counseling sessions with a dietitian and monthly counseling. They lost 4.5 pounds (two kilograms) or 2.1 percent of their body weight.
By the end of the study, more than half of participants in either the center-based or telephone-based intervention groups had at least five percent weight loss, compared to 29 percent for the control group.
"Findings from this study suggest that this incentivized structured weight loss program with free prepared meals can effectively promote weight loss compared with usual care group," the authors said.
"Importantly, weight loss was largely maintained at two-year follow-up."
They noted that even small weight changes can reduce the risk for cardiovascular disease and diabetes.
Participants received 25 dollars every time they visited the clinic.
The second, intensive one-year study led by Bret Goodpaster of the University of Pittsburgh School of Medicine, reached similar conclusions.
It evaluated 130 severely obese adult men and women without diabetes, randomly assigning them to either a group that dieted and exercised for all 12 months, or another group with the same dietary intervention but with physical activity delayed for six months.
Exercise included walking briskly for up to 60 minutes for five days a week for a target of at least 10,000 steps a day. Participants also received small financial incentives to reach their goals, regular contact with a nutritionist and some free meals.
After six months, the group that began with the diet and physical activity lost more weight in the first six months than the group that delayed exercise -- 24 pounds (11 kilograms) versus 18 pounds (eight kilograms).
But by the end of the study, weight loss was nearly identical for both groups -- nearly 27 pounds (12 kilograms) against 22 pounds (10 kilograms).
The researchers noted that participants in both groups also had reduced waist circumference, blood pressure, insulin resistance, visceral abdominal fat and liver fat content.
"Intensive lifestyle interventions using a behavior-based approach can result in clinically significant and meaningful weight loss and improvements in cardiometabolic risk factors in severely obese persons," they concluded, urging patients to incorporate exercise early in any weight loss program.
Obesity is among the most serious public health problems of the 21st century, the papers said, noting that obesity has spread rapidly over the past three decades, especially among African-American women.
In the United States, 68 percent of the population is overweight or obese, conditions that can also put people at increased risk of diabetes, high blood pressure and other medical problems.