Tests on rats showed those born to mothers fed a high-fat diet had many more brain cells specialised to produce appetite-stimulating proteins.
The Rockefeller University team say the finding may help explain why obesity rates have soared in recent years.
Previous research on adult animals had shown that when fats known as triglycerides circulate in the blood they stimulate the production of proteins in the brain known as orexigenic peptides, which in turn stimulate the appetite.
The latest study suggests exposure to triglycerides from the mother’s diet has the same effect on the developing foetal brain – and that the effect then lasts throughout the offspring’s life.
The researchers compared the offspring of rats fed a high-fat diet for two weeks with those whose mothers ate a moderate amount of fat. They found that the pups born to the high-fat diet mothers ate more, weighed more throughout life, and began puberty earlier than those born to mothers who ate a normal diet.
Lead researcher Dr Sarah Leibowitz said: “This work provides the first evidence for a foetal program that links high levels of fats circulating in the mother’s blood during pregnancy to the overeating and increased weight gain of offspring after weaning.”
The researchers suggest that the foetal brain is programmed so that the offspring can survive on the same diet as their mother – and they believe a similar mechanism may be operating in humans.
Dr Leibowitz said: “We are programming our children to be fat.”
Professor Ian MacDonald, an expert in the biology of obesity at the University of Nottingham, said there was clear evidence that nutrition before and soon after birth had an on-going impact on the genes.
But he warned against extrapolating too readily from animal studies, particularly as the rats in the latest study were fed a very unnatural diet.