Researchers at Duke University Medical Centre have carried out the study and found that obese men are three times more likely to see the cancer spread beyond the prostate than those of a healthy weight.
One of the researchers, Prof Stephen Freedland, said: "The study supports a growing body of literature showing that obese men with prostate cancer do worse. Our next step is to figure out why."
The researchers have based their findings on an analysis of 287 men whose diseased prostates had been removed, and who had then seen cancer return. All were given chemicals called androgen deprivation therapy (ADT) to limit levels of natural testosterone, which can trigger prostate cancer.
Those who were obese were three times more likely to have seen the returning cancer spread beyond the prostate after five years as those of a healthy weight, a process known as progression, `The Daily Telegraph` reported.
According to the researchers, the study suggests that rising levels of obesity in recent decades may be an important factor behind higher rates of prostate cancer, although the fact the population is ageing is thought to be even important.
Dr Christopher Keto, lead researcher, said: "Over the past decades, there has been increasing prevalence of obesity in the US and Europe, and a high rate of prostate cancer that is the second-most lethal cancer for men."
He, however, said more studies were needed to determine why obese men were more likely to see their cancers advance than healthy-weight men, even when given similar treatment regimes.
He suggested: "We think perhaps obese men may require additional ADT. The dose is the same regardless of weight, while most drugs are dosed according to weight."