Obesity 'programmed before birth'
Diet in pregnancy may have a lasting impact
Eating a high-fat diet in pregnancy may cause changes in the foetal brain that lead to over-eating and obesity early in life, research suggests.
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.
The study appears in the Journal of Neuroscience.
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.
We are programming our children to be fat
Dr Sarah Leibowitz
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.
They also had higher levels of triglycerides in the blood at birth, and as adults, and a greater production of orexigenic peptides in their brains.
More detailed analysis showed that, even before the birth, the high-fat pups had a much larger number of brain cells that produce orexigenic peptides - and they kept them throughout their lives.
The time to start feeding your child a healthy diet is right at the beginning of pregnancy
Dr Ian Campbell
Their mothers' high-fat diet appeared to stimulate production of the cells, and their subsequent migration to parts of the brain linked to obesity.
In contrast, rats whose mothers had a balanced diet had far fewer of these specialised cells, and they appeared much later after birth.
Lead researcher Dr Sarah Leibowitz said: "We believe the high levels of triglycerides that the foetuses are exposed to during pregnancy cause the growth of the neurons earlier and much more than is normal.
"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."
Dr Ian Campbell, medical director of the charity Weight Concern, said it had already been known that a high-fat diet in pregnancy made a child prone to a preference for fatty foods - but it had not been clear why.
He said: "The message is clear. We are not just 'what we eat'; we are also to some extent 'what our mothers eat'.
"The time to start feeding your child a healthy diet is right at the beginning of pregnancy."
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.