April 28 (HealthDay News) -- Obese people who underwent surgery that reduced the amount of food they could ingest not only lost weight, they also lost some of their lower back pain, according to a new report.

Thirty-eight morbidly obese patients with low back pain who underwent gastric bypass surgery reported that their pain decreased by an average of about 44 percent six months after surgery, according to researchers at the University of Southern California. The average amount of individual weight loss among the group of 30 women and eight men was about 85 pounds.

"This study provides evidence that substantial weight reduction following bariatric surgery results in moderate reductions in pre-existing back pain within six months of weight loss. While this initial research is promising, larger long-term trials are needed to prove the efficacy of this treatment," Dr. Paul Khoueir said in a prepared statement.

Khoueir was expected to present the findings in Chicago April 29 at the annual meeting of the American Association of Neurological Surgeons.

According to recent statistics, more than one-third of U.S. adults -- more than 72 million people -- were obese in 2005-2006. An estimated 75 percent to 85 percent of all Americans will experience some form of back pain during their lifetime.

Obese people are known to have a higher rate of hip and knee arthritis, but little is known about the extra weight's effect on lumbar spinal degeneration. While obese patients with back pain are frequently advised to lose weight, the association between these medical conditions remains unproven.

SOURCE: American Association of Neurological Surgeons, news release, April 28, 2008