For some men, weight loss plays an important role in raising low testosterone levels, a new study finds.

In the study of overweight, middle-aged men with prediabetes, about half of those with low testosterone levels who attempted to lose weight by changing their lifestyle experienced an increase in their testosterone levels.

The findings suggest “doctors should first encourage overweight men with low testosterone levels to try to lose weight through diet and exercise, before resorting to testosterone therapy to raise their hormone levels,” said study researcher Dr. Frances Hayes, a professor at St. Vincent’s University Hospital, Dublin.

Hayes and colleagues analyzed information from nearly 900 men with prediabetes — a condition in which blood sugar levels are abnormally high, but not high enough to be classified as Type 2 diabetes. The men's average age was 54.

The men were randomly assigned to receive one of three treatments: the diabetes drug metformin, an inactive placebo pill or lifestyle modifications, which consisted of exercising for 150 minutes a week and eating less fat and fewer calories. The researchers said they considered men to have low testosterone if their levels were below 300 nanograms per deciliter of blood.

Among the men assigned to change their lifestyle, about 20 percent had low testosterone levels at the study's start. After one year, that number fell to 11 percent.

Among those taking metformin, 24.8 percent had low testosterone at the beginning of the study, and 23.8 percent still had the condition a year later. For the placebo group, the rate fell from 25.6 percent to 24.6 percent during the study.

Men in the lifestyle modification group lost an average of about 17 pounds over the one-year study, and testosterone levels among men in this group increased 15 percent on average, the researchers said. (Men in the metformin group lost about 6 pounds.)

“Losing weight not only reduces the risk of prediabetic men progressing to diabetes but also appears to increase their body's production of testosterone,” Hayes said.

The study was presented this week at the Endocrine Society’s annual Meeting in Houston.