A new study by the Universities of Exeter and Oxford shows a clear link between a woman's higher energy intake around the time of conception and the birth of male infants. Writing in the journal Proceedings of the Royal Society B: Biological Sciences, the researchers speculate that the findings may help explain the falling birth-rate of boys in industrialized countries, such as the US.
The study involved recording the eating habits of first-time pregnant mothers in the UK. Analysis showed that 56 percent of the women in the group with the highest energy intake at conception had sons, compared with 45 percent in the lowest group. As well as consuming more calories, women who had sons were more likely to have eaten a higher quantity and wider range of nutrients, including potassium, calcium and vitamins C, E and B12. Interestingly, there was also a strong association between women eating breakfast cereals and producing sons.
Over the last 40 years there has been a small but consistent decline in the proportion of boys being born in industrialized countries. Study author Fiona Mathews thinks that this be related to a reduction in the average energy intake in developed nations and the fact that skipping breakfast is now common in the developed world.
"This research may help to explain why in developed countries, where many young women choose to have low calorie diets, the proportion of boys born is falling. Our findings are particularly interesting given the recent debate about whether to regulate 'gender' clinics that allow parents to select offspring sex, by manipulating sperm, for non-medical reasons. Here we have evidence of a 'natural' mechanism that means that women appear to be already controlling the sex of their offspring by their diet," said Mathews.
Other research has shown that animals have more sons when a mother has plentiful resources. The phenomenon has been most extensively studied in invertebrates, but is also seen in horses, cows and some species of deer. The explanation is thought to lie with the evolutionary drive to produce descendants.
"Potentially, males of most species can father more offspring than females, but this can be strongly influenced by the size or social status of the male, with poor quality males failing to breed at all. Females, on the other hand, reproduce more consistently. If a mother has plentiful resources then it can make sense to invest in producing a son because he is likely to produce more grandchildren than would a daughter. However, in leaner times having a daughter is a safer bet," Mathews explained.
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Source: University of Exeter