Weight loss was associated with increases in the male sex hormone testosterone and declines in the estrogen hormone estradiol in the study, which included 64 severely obese men in their late 40s; some had bariatric weight loss surgery and some did not.
Severe obesity has been linked to lower sperm counts and infertility in men, but the new research is among the first to show that it is also biologically linked to an unsatisfying sex life, says study researcher Ahmad Hammoud, MD, of the University of Utah.
Weight Loss Means Better Sex
On average, the men in the study weighed around 333 pounds at the start of the study and had a body mass index (BMI) of 46. Anyone with a BMI of 30 or more is considered obese.
Over the next two years, the men who had the weight loss surgery lost an average of 40 pounds and as much as 100 pounds, Hammoud noted.
The researchers measured total and free reproductive hormone levels at study entry and two years later. Study participants also completed questionnaires designed to assess their quality of life, including their sex lives, during the two time periods.
Weight loss and declining BMIs in men who had the surgery were directly linked to increases in total and free testosterone levels, declines in estradiol levels, and improvements in self-reported sexual quality of life
Hammoud says the findings offer important new insights into the impact of obesity and weight loss on sex drive and satisfaction.
"We know that weight loss, no matter how it is achieved, improves overall health," he says. "Now we see a direct relationship between weight loss, testosterone levels, and sexual performance."
Obese Men May Benefit from Treatment
The finding may also have implications for severely obese men who lose weight, he says. "If we treat these men with testosterone, it might improve their sex drive."
Hammoud says it is not clear if the findings apply to women, because sex drive in women is less strongly linked to hormones.
"We have shown that sexual satisfaction in women is better after bypass surgery, but we can't say if this is due to improvements in hormones or something else," he says.
Weight loss and bariatric surgery expert George Bray, MD, tells WebMD that he is not surprised that the men in the study experienced increases in testosterone as they lost weight.
His own research suggests that testosterone levels drop precipitously in men with BMIs of 40 and higher.
Bray is chief of the Clinical Obesity Center at Louisiana State University and a spokesman for the Endocrine Society.
"You would expect testosterone levels to be low in this group prior to weight loss, just as you would expect improvements following weight loss," he says.