Greater calorie intake increases chances of conceiving sons

I came across this article from ScienceNOW about a new study on whether the mom’s calorie intake at the time of conception affects the gender of the baby. The idea that it might is based on the Trivers-Willard hypothesis:

In 1973, biologist Robert Trivers and mathematician Dan Willard predicted that to maximize the number of her descendents, a mother should have some control over the sex of her offspring. If she’s healthy and has plenty of food, male offspring are her best investment because they can produce more progeny than can females. But a mediocre male cannot, so mothers with limited resources are better off having girls.

The study, You are what your mother eats: evidence for maternal preconception diet influencing foetal sex in humans, was done in the UK by Fiona Mathews, Paul J. Johnson, and Andrew Neil. Unfortunately, I couldn’t get access to the full text, so all I had to go by was the abstract and the article from ScienceNOW, but it sounds interesting. Mathews and her colleagues proposed that if the Trivers-Willard hypothesis is true for human mothers, a mother with greater total calorie intake might have more male babies.

The researchers looked at what the first-time mothers were eating at the time of conception. They found that of the mothers who consumed a total amount of calories in the top 1/3 of the subject pool, 56% had sons. In the lowest calorie group, 45% had sons. Male births are in a “small but detectable decline” in some industrialized countries- since 1970 the proportion of male births in the US has gone down by .1% – and now researchers have evidence that maternal diet may be one of the factors involved. There are likely other factors as well, such as environmental contaminants.

One of the interesting parts of the study is that it found a slightly stronger correlation between how much cereal the mother eats at the time of conception and the gender of the baby. Only 43% of mothers who ate less than one bowl of cereal per week had sons, while 59% of mothers who ate at least one bowl of cereal each day bore sons. From the ScienceNOW article:

With fewer women eating breakfast, Mathews says that the Trivers-Willard effect could be at least part of the explanation for dropping sex ratios. Breakfast may be particularly important for maintaining blood sugar levels, which have been linked to increased production of males in other mammals, although the precise mechanism is unknown (ScienceNOW, 30 November 2007).

I really wish I could read the actual article, because I’m particularly curious about this part. I eat lots of cereal – but rarely for breakfast. Rather, I munch on staples like cheerios for snack food at any time of day. The ScienceNOW article continually makes the jump from cereal to breakfast, and I want to know the details from the actual article. Did they ask whether they ate the cereal at breakfast time? If the effect is really about blood sugar levels, then the question of whether they ate breakfast may be more important than how much cereal they eat. And what about women who eat breakfast, keep steady blood sugar levels, but also keep a low overall calorie intake? Where did they fall?

Finally, I also take issue with the title of the ScienceNOW article, “Want a Boy? Eat your Wheaties.” While I understand that it is easier to stick to either X% have boys or X% have girls, I had a bit of a visceral reaction to the “Want a boy?” part of the title, because while I know I’ll be ecstatic and loving with my children no matter their gender, I’ve always daydreamed most often about a baby girl.

While an article title must provide a hook to get the potential reader to go read it, this title seems to me to really simplify the findings. Maybe something like “Want to choose your baby’s sex? Modify your diet.” would have gone down smoother but still hooked people. It seems like it would be easy for an average person to read the actual title and either think “That must be crap science” (this admittedly crossed my mind) or “I’m going to go eat Wheaties every day now.” In reality, from what I can gather with just the abstract and the ScienceNOW article, eating breakfast and/or cereal every day may increase your chance of conceiving a son to 59%. That is a significant increase, but the 41% of mothers who follow that and have girls is no small number of moms. And if I want to have a girl, should I start skipping breakfast and avoiding cheerios? That sure would seem foolish going into a pregnancy.


6 thoughts on “Greater calorie intake increases chances of conceiving sons

  1. I think that title is offensive too. They’re playing off of the historical prejudice for male offspring, and perpetuating it, albeit most likely unintentionally. As a reviewer I would have made them change the title to something like what you suggested above. This is scientists trying to be cute, and failing.

    You could email your comments about the methodology to the study authors. They might not have considered eating cereal at different times of the day. I think authors like fan mail. 🙂

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