Burgers for boys and chocolate for girls

Behind the Headlines

Thursday November 29 2007

Picture of a pregnant woman holding chocolate

Eating for a girl?

The food you eat can influence the sex of your baby, the Daily Mail claimed. “Eating a burger and chips can make your baby a boy", the newspaper said.

The story is based on research in mice that suggests that low blood sugar levels create conditions in the womb favouring the female X chromosome rather than the male Y chromosome. However, the authors of the paper do not suggest that the sex of children can be consciously influenced by changing the diet. It is always risky to extend the results from animal studies and presume they apply to humans; this research may have been misinterpreted. 


Where did the story come from?

Dr Elissa Cameron and colleagues from the Department of Zoology and Entomology at the University of Pretoria in South Africa carried out this research. The study was funded by the university and was published in the scientific journal: Proceedings of the Royal Society.



What kind of scientific study was this?

This was an experimental animal study. The researchers took 40 female mice and divided them into two groups of 20, a treatment group and a control group. Both groups had blood tests when they were 56 days old and were left with male mice for three days and nights. The treatment group had the steroid hormone dexamethasone added to their water for the three days when the male mouse was around. Dexamethasone lowered the blood sugar (glucose) levels of the mice at the time of conception.



What were the results of the study?

The authors found that the average blood sugar level in the mice differed between the hormone-treated group and the control group. The sex ratio of male to female offspring also differed significantly between the groups. The hormone-treated group gave birth to fewer male mice (41.9%) than the control group (53.5%).


“The results demonstrate a mechanism to explain how sex ratio can be influenced inside the uterus of mice as a result of changing glucose concentration”.

Elissa Cameron, lead author

The authors looked at the association between the sex ratio of the offspring and the change in blood sugar levels in the mice, the treatment with dexamethasone itself and the blood sugar levels before and after treatment. They found that the strongest association was between the sex ratio of the mice and the change in blood sugar levels caused by the hormone treatment.


What interpretations did the researchers draw from these results?

The researchers claim that these results “demonstrate a mechanism to explain how sex ratio can be influenced inside the uterus of mice as a result of changing glucose concentration”. They note that although the change in blood sugar level showed the strongest link with sex ratio, other factors are probably also involved. Once they had discussed their findings in light of other theories about the hormonal control of fertility, the researchers concluded that “in tandem with other mechanisms” the variation in blood sugar levels may influence the sex of an offspring.



What does the NHS Knowledge Service make of this study?

This study contributes to a  better understanding of sex selection in mice, but it is an over-interpretation of the data to suggest that there is now a way that humans can determine the sex of their children. 


This was a small study which showed about 8% fewer male mice born than expected in litters of several mice. Pregnancy in mice is influenced by different factors than other species where only one or two offspring are produced per pregnancy. Those communicating the results of animal studies need to be careful about drawing too many conclusions for humans, especially when making the leap from the reproductive process in mice and men.


Sir Muir Gray adds...

Don’t rely on this study to help you choose the colour of the nursery.


Analysis by Bazian

Edited by NHS Choices

Links to the headlines

How eating a burger and chips can make your baby a boy (and chocolate will produce a girl). Daily Mail, November 29 2007

Links to the science

Cameron EZ, Lemons PR, Bateman PW, Bennett NC. Experimental alteration of litter sex ratios in a mammal. Proc R Soc Lond B Biol Sci 2007; Nov 27 [Epub ahead of print]


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