Add a better prognosis for prostate cancer to the list of benefits that come from maintaining a healthy weight.

A study in the journal Clinical Cancer Research found that men who gain weight rapidly between the ages of 25 and 40 or who are obese at the age of 40 or at the time of prostate cancer diagnosis face a higher risk of the cancer returning.

The study included 526 men who underwent surgery to treat their prostate cancer following diagnosis. The men reported their body weight at age 25, 40 and the time of prostate cancer diagnosis, and then were followed for an average of 54 months.

During the follow-up period, 18% of the men developed biochemical failure, which is an increase in prostate-specific antigen (PSA) levels in the blood. A rise in PSA is an indicator for prostate cancer or its progression; following surgery, PSA levels should be undetectable, the study's authors say.

But the researchers found that men who gained weight rapidly in adulthood had double the risk of elevated PSA levels.

The magic number for rapid weight gain? "Three and a half pounds (1.5 kg) a year," said the study's lead author, Dr. Sara S. Strom of the University of Texas M.D. Anderson Cancer Center in Houston, in a news release. Among those whose cancer did recur, men who gained weight rapidly after the age of 25 also experienced progression sooner than men who gained little or no weight on an annual basis after the age of 25, the researchers reported.