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HOUSTON -- Obese hypogonadal men lost an average of 36 pounds during long-term testosterone replacement therapy (TRT), results of a prospective cohort study showed.

The men also shed 3.5 inches from their waistline as they lost fat mass and added lean body mass to their body composition. Overall, 95% of the 255 men lost weight during TRT for as long as 5 years, and 97% had reduction in waist circumference.

So far as investigators know, the men improved their physical status without really trying, as reported here at the ENDO 2012 meeting.

"The interesting part is that these changes were unintended. It was never the intention of treating these patients' testosterone deficiency to make them lose weight," Farid Saad, PhD, of Bayer Pharma in Berlin, said during a press briefing. "It was also unexpected. The literature doesn't show these data because the studies are short term, and you don't see anything of this magnitude in a 1-year trial or a 2-year trial.

"We think that this may be the result of a combined increase in vitality, improved lifestyle behavior, and increased energy expenditure, which is triggered by normalization of testosterone levels," he added.

Previous studies of TRT have shown changes in body composition, usually increased lean mass and decreased fat mass. In general, the studies have shown no net effect on weight.

The findings came from a review of data in a prospective registry of middle-age and older men (mean age 60.6) who received TRT for at least 2 years and for as long as 5 years. More than half of the patients had 4 years of follow-up.

The objective was to determine the long-term effects of normalization of testosterone levels in the men. Standard treatment was 1,000 mg initial dose, followed 6 weeks later by 1,000 and then 1,000 mg every 12 weeks after

The baseline testosterone level averaged 287 ng/dL. Baseline weight averaged 236 lbs., and 95% of the men had a baseline body mass index (BMI) >25, including 71% of men who obese (BMI 30 to 40) or morbidly obese (≥40). The men had a median waist circumference of 42.2 inches Similarly to weight distribution, 4% of the men had a waist <37 inches, and 68% had a waist circumference ≥40 inches

Testosterone levels normalized (≥350 ng/dL) within 6 to 9 months and remained stable throughout follow-up. Annual measurements showed that testosterone levels significantly exceeded baseline values (P<0.0001) beginning at 12 months and continuing to the end of follow-up.

Similarly, body weight declined significantly within 12 months and continued to decline for as long as 5 years (P<0.0001 versus baseline). Saad reported that weight declined significantly between annual measurements, beginning at year 2 (P<0.0001).

More than half of the men (53%) lost at least 33 lbs., and almost a third lost 44 lbs. or more weight. Similarly, 86% of the men had a least a 2-inch reduction in waist circumference, and 46% dropped 6 inches or more.

"This is an amazing response," said Saad. "I don't know many treatments where more than 90% of patients respond in a positive way to the treatment."

To put the results into perspective, Saad cited a clinical trial of the weight-loss drug sibutramine (no longer available), which showed an average weight loss of 7.6 lb after 5 years.

Saad said the principal concern about TRT involves its potential to induce or fuel the growth of prostate cancer. Three of the men in his study developed prostate cancer, which translated into a rate of 13.3 per 10,000 patient-years. That contrasted with rates of 116/10,000 and 96/10,000 in two large screening studies conducted in the U.S. and Europe.

"There is no evidence of an increased risk of prostate cancer in testosterone-treated men," Saad said. "When you look at [data from] the major urological conferences, like the American Urological Association, this is now the general understanding, that testosterone does not increase the risk of prostate cancer."

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