Researchers said that the results were a "grim message" for overweight young adults.
The study by scientists at the University at Buffalo in the US, shows for the first time that obese young men aged 14 to 20 have around half the total testosterone than normal weight youths.
Previously, the same research team had reported in 2004 that the presence of low testosterone levels, known as hypogonadism, in obese, type 2 diabetic adult males and confirmed it in 2010 in more than 2,000 obese men.
"We were surprised to observe a 50 per cent reduction in testosterone in this paediatric study because these obese males were young and were not diabetic," the study's first author Dr Paresh Dandona, professor in the Department of Medicine, said.
"The implications of our findings are, frankly, horrendous because these boys are potentially impotent and infertile. The message is a grim one with massive epidemiological implications," he said in a statement.
Dandona said in addition to the reproductive consequences, the absence or low levels of testosterone can also increase the tendency towards abdominal fat and reduced muscle, leading to insulin resistance which contributes to diabetes.
The study is published in the journal Clinical Endocrinology.