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For the record

Diet and determining your baby's sex

On the 23rd April 2008, a story ran about how a mother’s diet could affect the sex of her baby. One article in The Daily Telegraph said:

“In other words, women who want a son should eat a generous bowl of cereal for breakfast, munch bananas, use more salt and boost their overall daily calories by 400 calories - the equivalent of a meal.”  Read the article here.

Professor Richard Sharpe from the MRC Human Reproductive Sciences Unit at the University of Edinburgh, here replies:

A baby’s sex is determined by whether the sperm that fertilises the mother’s egg carries a Y or an X chromosome to join with the single X chromosome that is carried by the egg itself. So a baby’s sex is determined by the sperm not the egg.

A recent study1 suggested that a mother’s energy intake around conception can exert an influence on the sex of the baby. How such an effect is exerted is unknown, but the chances are that diet influences which sperm fertilises the egg rather than affecting survival/implantation of the fertilised egg.

It must be remembered that for every pregnancy there is around a 50% chance of conceiving a boy, and all of the claims for factors that increase or decrease this chance involve relatively minor changes to this ‘baseline’ value. Second, a woman’s diet and energy intake in pregnancy, especially in early pregnancy, can have effects on her baby’s growth and development. Therefore, for a woman planning a pregnancy, having a nutritionally well-balanced diet with not too many or too few calories is the best investment she can make in her baby’s future. Making major changes to her diet is not a good idea, unless it is in the direction of becoming better balanced, as the study authors say.

1 Mathews, F et al. 2008 You are what your mother eats: evidence for maternal preconception diet influencing foetal sex in humans. Proc. Roy. Soc. B: Biological Sciences   You can read the paper here  

Author: Sense About Science

Document type: For The Record

Published: 19 May 2008

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