TUESDAY, Oct. 18 (HealthDay News) -- When one member of a family has bariatric surgery to lose weight, other family members may be more likely to shed a few pounds, a new study finds.

Researchers tracked the spouses, children and other family members living in the homes of 35 obese people who had Roux-en-Y gastric bypass surgery. The patients and their family members attended three educational sessions before the surgery, and several sessions after the surgery that emphasized dietary and lifestyle changes to lose weight. That included advice on following a high-fiber, low-fat and low-sugar diet; information on appropriate portion sizes; and the need to limit alcohol and TV watching while getting enough sleep and sufficient exercise.

One year after the surgery, obese patients had lost about a third of their body weight, dropping from an average of 295 pounds to 197 pounds.

At the same time, other family members seemed to reap benefits. About 60 percent of spouses and other adult family members who lived in the home (such as parents) were also obese before the surgery, while about 73 percent of the children were obese.

After one adult in the house underwent surgery -- most often, a woman -- the average weight of the other obese family members dropped by 8 pounds (from 234 pounds to 226). Their waistlines also shrank, on average, from 47 inches to 44 inches.

Weight gain for obese children also seemed to level off, although weight loss among non-obese family members was not statistically significant, the researchers noted.

Family members also reported getting more exercise, drinking less alcohol (from about 11 drinks to 1 drink per month), and experiencing less "uncontrollable eating" or "emotional eating," according to the study.

Prior research has found that obesity may have a "social contagion" aspect to it, with people significantly more likely to become obese if their spouse, or even a sibling or friend, is obese, said senior study author Dr. John Morton, an associate professor of surgery at Stanford University and director of bariatric surgery at Stanford Hospital & Clinics.

"We knew that obese family members and spouses increases your risk of being obese. We thought, 'Well, can we make this work in reverse? If you have somebody who has lost weight, can they influence your weight in a positive matter?" Morton said. "And that's exactly what we found."

The study is published in the October issue of the Archives of Surgery.

Though an 8-pound weight loss is better than nothing, Dr. Mitchell Roslin, chief of obesity surgery at Lenox Hill Hospital in New York City, said the weight loss -- the equivalent of about 3 percent of body weight of the obese adults -- was "nominal."

"You'd rather these people lose 8 pounds in a year than gain it, but as a treatment modality, it's not going to be overly successful," Roslin said.

In addition, about 80 percent of those who had the surgery were women and 94 percent were college-educated. That suggests that weight loss interventions that target the whole family and "mom" in particular -- since she is most likely to be doing the grocery shopping and preparing meals -- may be very important, he added.

"When we do educational prevention programs, we have to involve the family unit as a whole," Roslin said. "There is a social role in eating."

However, he noted that the study results may not be the same among people with less education or who are in a lower socioeconomic group. "What they have here is a 'best-case scenario,' and it's easy to treat the best-case scenario," he said.

An estimated 26 percent of U.S. adults are obese (a body-mass index, or BMI, of 30 or above), which increases the risk of diabetes, heart disease and some types of cancer.

About 15 percent of children are obese, defined as having a BMI at the 95th percentile or higher using the U.S. Centers for Disease Control and Prevention growth charts. Having obese parents puts a child at sharply increased likelihood of being obese themselves.

Morton said that losing weight by other means than bariatric surgery could show similar a impact on family members. "What makes bariatric surgery unique is the results are so dramatic and so consistent and that reverberates through the family," he said. "When they see the terrific changes in terms of health, that gives them hope."

More information

The U.S. National Library of Medicine has more on bariatric surgery.