Two studies published on Monday by the Journal of Clinical Oncology recommend that patients should maintain a normal body weight to reduce the risk of aggressive tumours.
The studies examined the relationship between obesity and reappearances of prostate cancer across a broad range of men who had had their prostate gland removed due to cancer.
One study team, led by Christopher Amling of the Naval Medical Centre's Department of Urology in San Diego, examined more than 3000 prostate cancer patients, 19% of them obese.
Another study, led by Stephen Freedland of Johns Hopkins School of Medicine at Baltimore, Maryland, examined more than 1000 people, 22% of them obese.
According to Amling and Freedland, proteins and hormones contained in body fat might possibly favour the growth of cancerous prostate tumours among obese men.
"I would advise patients to maintain a normal body weight to limit the possibility that they would develop clinically significant, more aggressive prostate tumours"
Naval Medical Center's Department of Urology
"The primary role of obesity in prostate cancer is still unclear, but it appears to induce the development of more aggressive tumours," said Christopher Amling.
"I would advise patients to maintain a normal body weight to limit the possibility that they would develop clinically significant, more aggressive prostate tumours."
Prostate cancer is one of the most commonly diagnosed cancers in men.
The prostate is a small gland situated near a man's bladder and produces one component of semen.
If found early chances of survival are excellent, and modern surgical techniques and drugs mean that life-saving operations do not have to signal the end of sex lives.
The causes of prostate cancer are not yet understood, but there is some suggestion that a fat-rich diet may contribute to it.