But even when fed a healthy diet, the offspring of the junk-food-fed mothers are fatter than the offspring of rats fed healthy food. Moreover, obesity-linked genes are more active in the offspring of junk-food-fed mothers -- especially female offspring.
"The maternal diet seems to influence and trigger events early in the life of their offspring," study researcher Stephanie Bayol, PhD, tells WebMD. "We found that by the end of their adolescence, the offspring from the junk-food-fed animals had increased blood sugar, blood fat, and decreased insulin sensitivity -- all of which are associated with overweight and diabetes."
Bayol and colleagues at London's Royal Veterinary College gave pregnant rats normal rat chow. But they also gave them free access to cookies, chocolate, doughnuts, muffins, potato chips, candy, and cheese.
In earlier studies, they showed that the offspring of these rats liked high-fat, high-salt, high-sugar foods better than other rats. But the new studies show that even when never fed junk food themselves, the rats whose mothers ate junk food during pregnancy grew up fatter than normal rats.
"Their fat cells were larger, which might make them more prone to obesity and might make it harder for them to lose weight," Bayol says. "So there were lasting effects from their mother's consumption of junk food, even if they were not fed junk food after weaning."
Interestingly, the effects seem to be stronger for female offspring than for males.
"Males seem to use a different molecular machinery to regulate fat storage than do females," Bayol says.
Does the same thing happen in humans? Of course, it would be unethical to feed junk food to pregnant women. But there's evidence that women's diets during pregnancy and breastfeeding affect their children's food preferences, says pediatrician Stephen R. Cook, MD, MPH, of Golisano Children's Hospital at the University of Rochester, N.Y.
"This gets to the concept of fetal programming. A lot of information suggests that in-utero exposures can lead to long-lasting effects in children," Cook tells WebMD. "Women who smoke during pregnancy have children who are heavier, so maternal patterns can affect a child's weight. Whether the cause is altered metabolism or something else, it is a very real concern."
On the other hand, Cook says, junk food is made to have tastes and textures that appeal to children. And it's heavily advertised, which also affects a child's preferences.