Women who diet during pregnancy are 30 per cent more likely to have babies who develop schizophrenia later in life, say researchers.
The study of more than half a million expectant mothers found that those who did not gain the medically recommended amount of weight - between 1.5and 2stone - had a significantly greater risk of having a child who developed the severe mental illness in adolescence.
The Swedish team behind the study claimed that celebrity-led pressure on women to 'snap back' after giving birth was partly to blame.
Supermodel Gisele Bundchen caused controversy in 2013 when she flaunted her washboard abs on the cover of Vogue Brazil in shots taken just two months after giving birth to her youngest daughter, Vivian.
A number of other high-profile women, including the Duchess of Cambridge and Hollywood actress Jessica Alba, have also faced criticism for dramatically slimming down within weeks of giving birth.
The new findings come after warnings last week that obese pregnant women had a higher risk of having a child with cerebral palsy.
The average weight gain for a non-overweight woman during pregnancy is between 22 lb and 27 lb, according to NHS guidelines. However, anything up to 35 lb is said to be within the healthy range.
The latest research, carried out at Karolinska Institutet in Stockholm, was based on 526,042 Swedes born between 1982 and 1989.
Thanks to the country's extensive nationwide health and population registers, researchers were able to follow them into adulthood and found that nearly 3000 had gone on to develop non-affective psychoses, or schizophrenia.
They found a correlation between gestational weight gain below the medical guidelines and serious mental illness in the offspring - regardless of the mother's initial body type.
"Extremely low weight gain during pregnancy - less than 18 lb for normal-weight women - was associated with a 30 per cent increased risk of offspring with non-affective psychoses, compared to women who gained the recommended amount of weight for their body type," said lead author Euan Mackay.
"The results were similar regardless of whether women had started pregnancy with larger or smaller body types."
And Assistant Professor Renee Gardner, of Karolinska's Department of Public Health Sciences, said: "This inadequate weight gain can also reflect societal pressures for women to maintain an idealised body type, even when they are pregnant."
Sir Robin Murray, Professor of Psychiatric Research at the Institute of Psychiatry, Psychology and Neuroscience, King's College London, said: "This does not mean pregnant women should overeat, and the advice remains the same: eat a balanced diet and keep healthy during pregnancy, take folic acid, and don't smoke tobacco or use illicit drugs.
"Genetic predisposition, child abuse and adverse life events all contribute to schizophrenia-like psychosis."