A mother's diet around the time of conception can permanently influence her baby's DNA, research suggests.
Animal experiments show diet in pregnancy can switch genes on or off, but this is the first human evidence.
The research followed women in rural Gambia, where seasonal climate leads to big differences in diet between rainy and dry periods.
It emphasises the need for a well-balanced diet before conception and in pregnancy, says a UK/US team.
Scientists followed 84 pregnant women who conceived at the peak of the rainy season, and about the same number who conceived at the peak of the dry season.
Nutrient levels were measured in blood samples taken from the women; while the DNA of their babies was analysed two to eight months after birth.
Lead scientist Dr Branwen Hennig, from the London School of Hygiene & Tropical Medicine, said it was the first demonstration in humans that a mother's nutrition at the time of conception can change how her child's genes will be interpreted for life.