High protein, low carbohydrate diets should be avoided during pregnancy as they can lead to more stressed offspring, research suggests.
Maternal diet can affect a baby's long term health
A UK team followed a group of 86 children born in 1967-8 to mothers who were told to eat a pound of red meat a day to avoid pregnancy complications.
The study found the more meat the mother ate, the higher the levels of stress hormone cortisol in the child.
The research is being presented at a medical conference in Glasgow.
The subjects, now in their 30s, were asked by the teams from the Universities of Edinburgh and Southampton to perform a series of stressful tasks including public speaking and mental arithmetic.
Their blood pressure levels were recorded and cortisol levels were measured before and after each task.
Dr Rebecca Reynolds, who led the study, said it was designed to see how events in pregnancy could affect the health of offspring in later life.
"We are very interested in foetal programming which says how we are born as a baby sets us up for future health."
The women from Motherwell, Lanarkshire, included in the study were advised by an obstetrician to eat very high levels of meat and low levels of carbohydrate to avoid a condition called pre-eclampsia associated with high blood pressure in pregnancy, she said.
"This study adds to the increasing evidence of the importance of the maternal diet and suggests that one of the ways in which it can have these long term effects is by permanently altering stress hormone levels.
"We don't know why this occurs - it may be that the baby is put under stress during pregnancy which causes irreversibly high levels of cortisol."
But she added: "Given the recent popularity of low-carbohydrate/high protein diets, such as the Atkins diet, this data also suggests that these diets should be avoided during pregnancy."
Dr Doris Campbell, reader in obstetrics and gynaecology at Aberdeen University, said it was probably not a good idea to mess around with diet during pregnancy.
She said that energy restriction was not good during pregnancy and that most pregnant women simply ate to appetite - which tended to grow to compensate for increased tiredness.
"These sorts of high protein, low carbohydrate diets are not particularly healthy in general, but I certainly would not advocate them in pregnancy," she added.
The research is being presented at the European Congress of Endocrinology in Glasgow on Tuesday.