For people who are severely obese and struggling with their weight, new research shows weight-loss intervention programs that combine diet and exercise really can work.

Though the benefits of diet and exercise have long been known, these studies show the impact lifestyle changes have on people who are severely obese, said researchers from the University of Pittsburgh School of Medicine.

That means people who can't afford to or choose to not undergo bariatric surgery have other options that have been shown to be effective, said Dr. Donna Ryan, president of physician and researcher organization The Obesity Society, who was not involved in the studies.

"Most people are very pessimistic about what kind of weight loss you can achieve with lifestyle changes," Ryan told MyHealthNewsDaily. "But this intervention was in a seriously obese population, and that is the big take-home message: that very heavy people can benefit from lifestyle change."

In 2009, nearly 27 percent of people in the United States were obese, according to the Centers for Disease Control and Prevention.

By controlling the size of food portions, and finding motivation to be active through a friend or personal trainer, weight-loss interventions can work for people who are morbidly obese, said registered dietitian and American Dietetic spokesman Jim White, who was not involved with the studies.

The studies were published online today (Oct. 9) in the Journal of the American Medical Association.

Diet and exercise

In one new study from the University of Pittsburgh School of Medicine, researchers implemented a weight-loss program with 130 severely obese adults, ages 30 to 55, who had a body mass index (BMI) between 35 and 39.9.

A BMI between 18.5 and 24.9 is considered healthy; a BMI of 30 or higher is considered obese.

The adults in the study were randomly assigned to two groups. One group underwent exercise and diet interventions for 12 months, which consisted of an hour of brisk walking five days a week, or at least 10,000 steps a day, and liquid and pre-packaged meal replacements for certain meals throughout the day.

The other group had the same meal replacements for all 12 months, but were given the exercise instructions during the last six months of the study.

After six months, the group that had both diet and exercise interventions lost more weight. They lost an average of 24 pounds (10.9 kilograms), compared with 18 pounds (8.2 kg) lost by the other group. By the end of the 12-month period, the first group had lost almost 27 pounds (12.1 kg), and the other group lost 22 pounds (9.9 kg), the researchers said.

Waist circumference, liver and abdominal fat, blood pressure and insulin resistance – a risk factor for diabetes – were all reduced by the intervention, too, the study said.

Hidden benefits

"Not only is weight loss good, but usually the energy level goes up," White said, and the other health benefits – such as lower blood pressure and insulin resistance –are unseen but just as important.

In the second study, 442 overweight or obese women, ages 18 to 69, were given free prepared meals and weight-loss counseling, or just weight-loss counseling. After two years, the women who received the prepared meals lost about 16 pounds (7.4 kg), whereas the women who had received only the weight-loss counseling lost 4.4 pounds (2 kg), according to the study.

"A regimented program can definitely help," White said.

This article was provided by MyHealthNewsDaily, a sister site to LiveScience.