What to make of this study?
"It's interesting," said Keith Ayoob, an associate professor at Albert Einstein College of Medicine in New York City. "But it's a long way from saying this happened in mice, and that explains the obesity epidemic in this country."
Ayoob, who counsels families to help children lose weight, says he'd rather look at individual eating habits while he waits for researchers to examine Gewirtz' work.
Until then, "I would say a lot more research is needed."
There's no doubt that some families are naturally thin, and others are naturally husky.
But new research out of Stanford University has indicated that even the success of a diet could be predicted by your genes.
Recently Waltham, Mass.-based Interleukin Genetics, Inc., paid for DNA testing of 138 women who had taken part in a diet study in 2007. In the previous study women were assigned to a low-carb, low-fat or general diet.
Stanford researchers then compared the women's weight loss success with their genetic profile of three genes that show a pattern for metabolizing fats and carbohydrates, according to the Associated Press.
They found that if women's genes indicated they would metabolize fats better, they lost more weight on a low-fat diet than a low-carb diet. The reverse was true for women whose genes indicated they metabolized carbs better, Mindy Dopler Nelson, a nutritional biologist at Stanford University, reported at an American Heart Association conference last week.
Women whose diets matched their genes lost 10 more pounds over a year compared to women on mismatched diets, Nelson reported.
So is it really a question of finding your genetic diet match?
Ayoob had a cheaper solution while more studies examine the link.
"The smartest thing to do is look at where the excess is in your diet," said Ayoob.
Frequently patients coming to Ayoob need help kicking obviously bad habits that lead to weight gain. For example, Ayoob said, some people have a weakness for sugary drinks. Others, he said, miss breakfast and then have a problem gorging and snacking through the day.
"You want to be comfortably hungry when you eat," said Ayoob. "When you're starving you're going to make poor choices."
If your gut bacteria or your genes are not at fault, how about looking at your circle of friends as a source of obesity?
In 2007, an article in the New England Journal of Medicine used 30 years of data on 12,000 people to show obesity and weight loss may actually be contagious -- things that spread among people who know each other.
"They key idea is that people are influenced by the behavior and actions of those around them. This applied to something that people may not have thought of, which is body size," said Dr. Nicholas A. Christakis, author of the recent book "Connected," which looks at how various phenomena from depression to obesity spreads through society.
Over the three decades, Christakis showed how obesity in one person in a circle of friends statistically meant more people in their circle of friends would become obese. The same was true of weight loss.
"We're not saying we found the cause of the obesity epidemic. We're not," said Christakis. "Social networks have a general property that they magnify what they are seated with."