A recent study with pregnant female rats indicated that the pups of those rats who were offered junk food ended up opting for junk food at far higher rates than the pups of moms that were under a regular chow regime.
…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.
And:
For most of our evolutionary past, the problem has been avoiding starvation. An environment awash with sugars and fats is, therefore, an evolutionary novelty: in hundreds of millions of years of evolution, this is the first time such foods have been abundant. Giant quantities of fats and sugars have not, historically, been available to a developing fetus, so it wouldn’t be surprising if they do have a harmful impact.
If this is right, it raises the alarming possibility that the obesity epidemic has a built-in snowball effect. If children born to obese mothers are, owing to the environment in the womb, predisposed to obesity, they may find staying thin especially hard. Reversing the epidemic may thus rest on helping women to lose weight before they conceive and helping them to eat a balanced, non-junk-food diet while they are pregnant. The well-being of the next generation may depend on it.