Researchers have known that a pregnant mother’s diet can have a lasting impact on her child’s susceptibility to cancer, diabetes, obesity, and depression. Randy Jirtle, an oncologist at Duke University, is the first to decode the reason why. He and his colleagues studied dietary effects on two groups of genetically identical mice. The researchers fed one group of pregnant mice a normal diet. The second group ate the same food but also received a cocktail of B12, folic acid, choline, and betaine. The mice that got the extra nutrients had reduced expression of a gene that causes obesity, diabetes, and cancer. Jirtle says the nutrients probably help by providing a ready supply of methyl molecules, which act as stop signals at key places in the genome. “Roughly half of our DNA is junk—leftover bits of unnecessary genes and DNA fragments introduced by viruses. If we expressed all these genes, we’d be a mess, so we evolved an effective off switch. But the switch doesn’t work if it doesn’t have just the right amount of raw materials it needs,” he says.
The methyl molecules have the greatest impact during periods of rapid cell division, such as when an embryo is only a few cells old. If the mother is nutritionally deprived or oversupplemented at those times, the expression of some genes in the child will be permanently altered. Methyl markings are then passed on along with the rest of the DNA, so the effects of malnutrition could be passed along for generations. “This is the first example of how early environment can alter gene expression without mutating the gene itself,” Jirtle says.