The team at Yale School of Medicine, in the US, showed diet could change the structure of mice brains.
They argue this could explain why the children of obese parents are more likely to become grossly overweight.
Experts said the study had merit, but brain changes in humans were unproven.
Obesity can run in families and shared eating habits are a major factor.
However, there is evidence that diet during pregnancy can also influence a child’s future waistline, such as through changes to DNA.
‘Signal to the pup’ The latest foray into the field, published in the journal Cell, shows the structure of the brain itself may be changed.
The experiments on mice showed that mothers on a high-fat diet had pups with an altered hypothalamus, a part of the brain important for regulating metabolism.
These mouse pups were more likely to become overweight and develop type 2 diabetes than the pups of mothers given a normal diet.
One of the researchers, Prof Tamas Horvath, from Yale, told the BBC: “It could be a signal to the pup that it can grow bigger as the environment is plentiful in food.
“We definitely believe these are fundamental biological processes also affecting humans and influencing how children may eventually become obese.
“It seems, at least, that this could have a major impact and we need to explore it further in both animal and human studies.”
He says a healthy diet during pregnancy may help to break the cycle of obese parents having obese children.
‘Neurological circuits’ Commenting on the findings, Dr Graham Burdge, from the University of Southampton, told the BBC: “Twenty years of research shows nutrition in early life has lasting effects on cardiovascular disease, obesity, osteoporosis and some cancers. It’s extremely well established.
“This is an intriguing technical advance showing neurological circuits are being changed, which hasn’t been shown before.” He said the “concept fits in well with the data” but pointed out there were key differences in the way mice and people process fat, so the same might not be happening in pregnant women.
He added: “Much of what we know about the process comes from animals. The next big thing is to establish the same mechanisms operate in humans and if we can modify that.”
For now he advises parents to “have a healthy balanced diet and ensure the diet of your child is balanced as well”.