A recently published study found a relationship between female diet prior to conception and the "sex ratio" in humans. Sex ratio is the relative number of females born to males. Specifically, women who consumed a greater amount of calories prior to conception had a higher percentage of boys. In trying to identify specific foods, the authors found that women who had breakfast cereal daily were more likely to have boys. No other foods showed a significant relationship.

Background

In mammals other than humans, parents seem to have the ability to alter the percentage of males born versus females. Studies have shown that when "resources" are plentiful, more males are produced. Scientists feel that this makes sense from an evolutionary perspective. It takes a greater amount of resources in both the short term and long term to produce males. It is agreed that since humans have relatively few offspring compared to other mammals, and since carrying a pregnancy to term requires a significant amount of time and effort from the mother, the ability to alter the ratio of males to females at different times would make sense. The mechanism for controlling the sex ratio in mammals is thought to be due the ability to alter the conception and viability of male and female embryos. The high availability of resources around the time of conception is consistently linked with an increased likelihood for males.
 
In a recent study, the authors set out to determine whether the same mechanisms that operate in other mammals, also operate in humans.
 

Study on the influence of diet on the gender of children

This study was conducted in the south of England. Women pregnant with a single baby with no previous deliveries and who were not obese, were recruited from prenatal clinics early in their pregnancies. 740 women kept a food diary in the early part of their pregnancy. Of these, 721 women also reported on their diets in the year prior to conception. 661 women also kept a food diary in later pregnancy. During the study, women were not given any information about the gender of their baby if it was determined by ultrasound or amniocentesis. After delivery, the researchers tabulated the number of male and female babies and then tried to determine whether there was any relationship to the diet the women reported.
 

Study results 

The only significant finding was that a woman’s diet before conception seemed to be associated with the gender of the baby born. Specifically, women who ate a greater amount of food were more likely to have a male baby. Food intake was measured by total number of calories consumed. Women who were in the highest third for calories consumed were 1.5 times more likely to have a boy compared to women who were in the lowest third. 
 
Researchers then sought to determine whether a specific food or nutrient was influential in determining the gender of the baby. The interesting result was that breakfast cereal was strongly associated with infant sex. Women producing male infants ate more breakfast cereal on average than women who produced female infants. Women who ate at least one bowl of breakfast cereal daily were 1.87 times more likely to have a boy compared to women who ate one or less bowls of cereal per week. 
 
These results could not be due to an overall skewing in the sex ratio since overall about 1/2 the babies were boys and 1/2 were girls. Furthermore, the age of the mother was not linked with the likelihood of having a boy or girl. The weight of the mother also did not predict the gender of the baby.
 

Discussion

There has always been much interest in methods to sway the odds of having a male or female child. Throughout history, methods have been employed that utilize the lunar calendar, timing intercourse relative to ovulation, and altering the acidity of the vagina prior to intercourse. None of these methods have any reasonable supporting data however.
 
More recently, emphasis has shifted toward attempting to use technology to achieve gender selection. Various methods have been proposed to select sperm containing "X" or "Y" chromosomes to fertilize eggs. In all but one instance, these methods have also failed to alter the sex ratio beyond what might occur from chance. The only successful method, which is expensive, has a success rate of 70-75%. PGD or preimplantation genetic diagnosis is a technique used during IVF to determine the gender of embryos by looking at the chromosomes. This technique is essentially 100% accurate but expensive and invasive for the female.
 
It seems that by altering the diet, women may be able to alter  their chances of conceiving a male or female by either eating breakfast cereal every day prior to conception (to help have a male) or skipping breakfast and perhaps decreasing the total amount of calories consumed (to increase the chances for a female). 
 
The chances for success however, do not approach that of IVF with PGD. Frequent cereal eaters ultimately saw 60% of their babies were boys compared to 40% boys from the non cereal eaters.