”Eat breakfast if you want your baby to be a boy”, the headline in the Daily Mail read today. Women are “more likely to have boys if they eat plenty and, crucially, have breakfast every day. And if it is cereal, the odds are even more in a boy's favour”, the newspaper explains. This new scientific study investigating whether calorie intake around the time of conception can influence the sex of your baby has received widespread press coverage. The Mail reports that “this is the first scientifically proven way of influencing the gender of a baby without the need for expensive medical treatment” while The Independent says that “the trend to skip breakfast could be altering the male/female balance in the population”.
The findings will undoubtedly spark keen interest among the population at large. However, although this study has been carefully designed and conducted to see whether it is possible to form a theory on how natural conditions may influence the sex of a baby, it has many limitations and the results cannot be considered conclusive. The biological processes of reproduction and fertility may, to some extent, be influenced by our general mental and physiological health, which may include eating a healthy diet. However, the sex of a baby is ultimately determined by the fertilisation of the egg by a sperm carrying either an X or Y chromosome, not by the mother eating a particular food.
The most important message for couples hoping for a baby is that women cannot be guaranteed a boy, or probably even increase their chances of having one, if they eat breakfast and increase their calorie intake, or guaranteed a girl if they do the opposite.
Fiona Mathews of the School of Biosciences, University of Exeter, and colleagues of University of Oxford, carried out this research. The study was funded by the Sir Jules Thorn Charitable Trust. The lead researcher is a Royal Society Dorothy Hodgkin Research Fellow. It was published in the Proceedings of the Royal Society of Biology, a peer-reviewed scientific journal.
This was cross-sectional study of expectant mothers, designed to investigate the theory of whether parents can have any influence over the sex of their offspring. The researchers say that little is known about the natural mechanisms of sex allocation in humans, although one of the best known theories on how the sex ratio between males and females evolved historically, is that improved parental conditions “enhances the reproductive success of sons”. As sons are potentially able to produce a larger number of offspring than daughters, and therefore promote the human species, then “parents in good condition should favour male offspring”.
It is uncertain whether these patterns would be true in today’s society, where resources are more plentiful so that more parents should be in a ‘good condition’. Social and relationship structures are also different, and males are less likely to ‘mate’ with a large number of females than they may have done hundreds or thousands of years ago. This is what the researchers aimed to investigate.
Healthy women, who were about 14 weeks pregnant with their first baby, without any medical conditions and of a healthy weight, were recruited from a hospital in the south of England at their first antenatal visit. Recruitment was stratified to include a proportion of smokers representative of the numbers in the general population. A total of 740 women were recruited and they kept diaries of their seven-day food intake during early pregnancy. Of the total 97% also reported on their diet in the year prior to conception in a food frequency questionnaire and 89% completed another seven-day food diary later in the pregnancy, at 28 weeks. None of the women were aware of the sex of their babies.
The researchers summarised nutritional patterns from the three time points: preconception food intake, early pregnancy intake at 16 weeks and later pregnancy intake at 28 weeks. They used statistical tests to see whether nutritional contents remained the same over time, and how the sex of the baby related to the nutritional intake of the mother.
The researchers found that there seemed to be consistencies over time in the nutritional content of the food that the women ate. When they looked at whether this correlated with the sex of the baby, they found that intake of protein, fat, folate, vitamin C and a range of other trace minerals (they called these factor 1 nutrients) across the three time periods were only just significantly related, while vitamin A components and vitamin B12 (factor 2 nutrients) were not.
Looking at the three time periods separately, they found that only the diet in the year prior to conception significantly related to the sex of the baby. The women who had higher intakes of factor 1 nutrients in the preconception period were more likely to have a boy. The researchers say these scores are highly correlated to energy intake and energy intake in itself was significantly related to whether the woman had a boy baby.
When the researchers divided the women up into three categories of energy intake during the preconception period, they found there was in increase in the percentage of male babies with an increase in energy intake, i.e. those in the highest third were 50% more likely to have a male than those in the lowest third of energy intake.
Of the 133 food items tested, they found that there was only a significant relationship between baby’s sex and cereals. They then looked at whether a similar relationship existed to that of total energy when they divided the women up into thirds of cereal intake, and found that those eating one or more bowls per day were more likely to have a boy than those having less than one bowl per week.
The researchers found no other relationships between baby’s sex and mother’s smoking history, folic acid use, age, weight, height, BMI or mother’s educational level.
The researchers conclude that their results “support hypotheses predicting investment in costly male offspring when resources are plentiful”. They say mothers had a higher chance of having a boy if their nutrient intake was higher prior to pregnancy and that eating cereals seemed to be linked to having a male baby.
This research has been carefully conducted. However, these results can only show a link between the recalled dietary patterns of a group of women before they became pregnant and the eventual sex of their baby. They do not prove that it was the nutritional intake or that eating one particular type of food actually determined the sex of the baby.
At the current time it would seem ill advised to suggest to any couple that they could be guaranteed a boy, or even increase their chances of having one, if the woman eats breakfast and increases her calorie intake, or guaranteed a girl if she does the opposite.
This type of study is full of pitfalls; so much information is collected that two factors can have a statistical association, occurring together more likely than would occur by chance, without one being the cause of the other; don’t change your cereal intake on the basis of this alone.