Losing weight without going to the gym has become more difficult, especially for older adults, according to a study published in the journal JAMA Internal Medicine.

The researchers looked at how many calories people consumed each day without going out for a run, walking, cycling or other physical activity, and found that those who were not getting exercise had the highest risk of developing obesity-related diseases.

The study also found that women, those who had more children and those who exercised regularly had the lowest risk of obesity.

“We know that there are environmental factors that can make people more susceptible to obesity,” said lead author Sara A. Katz, PhD, an assistant professor of health sciences at the Johns Hopkins Bloomberg School of Public Health and the John F. Kennedy School of Government at Harvard University.

“But we’re not sure why that is.”

Katz and colleagues conducted the study by examining data from a large study of 1,564 men and women, ages 45 to 79, in the United States.

Researchers tracked their activity level, their body mass index (BMI), body fat percentage, exercise level, amount of exercise they did, and their physical activity level.

Those who did not go out for exercise had lower BMI, and those with a lower BMI were more likely to have lower activity levels.

Those with a higher BMI were also more likely than those who did exercise to have a higher activity level than those without a higher body mass Index (BPA) — a measure of body fat — but less likely to be overweight.

Katz said the study provides a “preliminary” picture of how exercise habits can impact obesity, but more research is needed.

“This is an important and necessary step in the direction of getting more people to be active, and that is certainly a good thing,” Katz said.

“Our study is very limited, but it does point to something.”

Katz noted that a healthy lifestyle — and the exercise habits of older adults — may be important for prevention of obesity and metabolic diseases, but that it is not enough to eliminate obesity.

More research is required to understand how physical activity influences obesity, Katz said, and to determine the relationship between physical activity and risk factors for obesity.