There's no shortage of good reasons for men to keep their weight under control. But now add one more: According to a new study, overweight men diagnosed with prostate cancer are significantly more likely to suffer a recurrence than men of normal weight.

One of the easiest ways to diagnose faltering prostate health is by measuring blood levels of prostate specific antigen (PSA) a protein produced largely—but not exclusively—by the prostate gland. When the prostate is removed during cancer surgery, PSA levels should fall to almost nothing. If they start to climb again, that's a worrisome sign of relapse.

Epidemiologist Sara Strom of the University of Texas M.D. Anderson Cancer center in Houston Studied 526 prostate cancer patients and found that those who were obese by age 40 were twice as likely to show rising PSA levels after surgery as those who weren't. In special danger, according to her findings, were men whose weight gain had come on relatively rapidly—about 3.5 lbs. per year—between ages 25 and the time of their diagnosis.

Strom's findings can help urologists and oncologists plan treatments and make prognoses for overweight men who develop prostate cancer. Just as important, they provide one more incentive for overweight men to shed extra pounds before they get sick, and for normal weight men to stay that way.