Olivia Judson in the NYT:
Suppose you have two groups of pregnant female rats. Rats in the first group can either eat as much regular lab-rat chow as they like, or they can eat their fill of human junk food — cookies, doughnuts, marshmallows, potato chips, muffins, chocolate. Rats in the second group only get chow, but again, can eat as much as they like. After the rats have given birth, continue the different regimens while the pups are suckling. Then give both groups of pups access to the chow and the junk food.
Experiments like this have found that pregnant females with access to junk food ate, on a daily basis, roughly 40 percent more food (by weight) and 56 percent more calories than rats that just had chow. Moreover — and this is the interesting bit — pups whose mothers ate junk food while pregnant and lactating had a greater taste for food high in fat and sugar than those whose mothers did not. The junk-food pups ate more calories and were more prone to gaining weight.
What goes for rats does not necessarily go for humans. Nonetheless, such results are thought-provoking. As everyone knows, humans are getting fatter and fatter. According to the World Health Organization, 400 million adults around the world weighed in as obese in 2005. In the United States, more than a third of women between 20 and 39 are obese, some of them extremely so. For the first time in history, large numbers of obese women are having children.