WASHINGTON British researchers who tried to show why overweight mothers tend to have overweight children said on Monday they had filled in one small piece of the puzzle.
Their reassuring finding: women who are too fat when pregnant are probably not somehow driving the obesity epidemic by programming their children to be fat.
But there is a strong link between overweight mothers and overweight children that still needs to be explained, Debbie Lawlor of Britain's University of Bristol and colleagues said.
Lawlor's team looked at the developmental overnutrition hypothesis -- the idea that if a woman is overweight during pregnancy, the higher levels of sugar and fatty acids in her blood would affect the developing fetus, dooming or at least predisposing the child to poor appetite control and a slower metabolism.
"The offspring of these mothers would be expected to be programmed to become more obese themselves," Lawlor's team wrote in their report, published in the Public Library of Science journal PLoS Medicine.
They studied 4,091 mothers, their children born in 1991-1992 and the fathers of these children. They also studied the DNA of everyone, height, weight and body mass index, which is a measurement of obesity, as well as smoking, education and other factors.
They did find that if a child became overweight by age 9 or 11, the mother was more likely to have been overweight or obese than was the father.
Then they looked at one gene that may explain this association -- the "fat mass and obesity associated," or FTO gene. FTO has been shown to predispose people to type 2 diabetes if they are overweight.
They found that people with certain variants of FTO are more likely to become overweight. Inheritance from the mother appeared to have a stronger effect, although why was not clear.
"At this stage, the exact mechanisms by which FTO results in increased BMI are not known. Consequently, we cannot discount it having an effect via dietary and physical activity behaviors," Lawlor's team wrote in the report, available online here
What they did conclude was that obese mothers are unlikely to be driving a growing obesity epidemic by having babies who are metabolically programmed to get fat as they get older.
But mothers are somehow involved in other ways, they added.
In a commentary, Frank Hu of the Harvard School of Public Health said the study was unable to disprove the overnutrition hypothesis.
Hu said the obesity epidemic is clearly alarming and other researchers should be doing studies like Lawlor's to make sure that a "vicious cycle" of obese mothers, children and thus grandchildren is not somehow causing it.
(Reporting by Maggie Fox, Editing by Philip Barbara)