A new study has shown a statistical leap in the rates of male children born to Mothers on a high calorie diet. University of Exeter biologist Fiona Matthews, who headed up this research, noticed specifically that mothers who have breakfast cereal daily and who eat high potassium foods (like bananas) are more likely to have sons. Ms. Matthews answered some of my questions recently, and I present her responses here unedited…
-What made you decide to study this? I noticed that most of your research is usually centered around wildlife. Is there a connection that you noticed between what you’ve seen in animals and your results on studying humans?
I’M INTERESTED BROADLY IN ENVIRONMENTAL EFFECTS ON REPRODUCTION AND DISEASE. THIS STUDY WAS SET UP AS A LARGE-SCALE RESEARCH PROJECT LOOKING AT THE EFFECT OF MATERNAL DIET BEFORE AND DURING PREGNANCY ON THE HEALTH OF THE MOTHER AND BABY (I’VE UPDATED MY WEBSITE SO THAT YOU CAN NOW GET PDFS OF MANY OF THE PAPERS). I HAD THOUGHT I HAD FINISHED ALL OF THE IMPORTANT ANALYSES AND TURNED MY ATTENTION TO OTHER MAMMAL SPECIES. I THEN BECAME AWARE OF A LARGE AMOUNT OF LITERATURE ON THE MANIPULATION OF SEX RATIOS IN WILD ANIMALS ACCORDING TO ‘MATERNAL CONDITION’ (A RANGE OF VARIABLES HAVE BEEN USED INCLUDING FAT RESERVES; HABITAT QUALITY ETC). I THEREFORE DECIDED TO GO BACK AND SEE WHETHER THESE RELATIONSHIPS EXISTED IN THE HUMAN DATABASE I HAD ALREADY COLLECTED.
-Have you read the study from a few years ago that showed a statistical increase in boys the longer a couple tries to conceive? Do you think there is a potential correlation between those results and your own?
YES, I HAVE READ THAT. THERE ARE ALSO PAPERS SUGGESTING LINKS BETWEEN THE TIMING OF CONCEPTION AND THE LIKELIHOOD OF A BOY, AND BETWEEN THE FREQUENCY OF INTERCOURSE AND THE LIKELIHOOD OF A BOY. AT THE MOMENT WE DON’T KNOW WHAT THE MECHANISM IS FOR SEX SELECTION IN HUMANS (AND WRETCHEDLY DIFFICULT TO EXTRAPOLATE FROM LABORATORY RESEARCH SINCE THIS GENERALLY DEALS WITH ANIMALS THAT HAVE MULTIPLE OFFSPRING AT A TIME, AND SO DIFFERENT MECHANISMS MIGHT OPERATE). IT IS THEREFORE POSSIBLE THAT THE EFFECT OF DIET MIGHT BE CONFOUNDED WITH ANOTHER VARIABLE. FOR EXAMPLE, IT MIGHT BE THAT WOMEN WHO HAVE SEX MORE OFTEN ALSO HAVE A HIGHER CALORIE INTAKE ON AVERAGE. AT THE MOMENT, WE SIMPLY DON’T KNOW WHICH OF THESE (IF INDEED THEY ARE CONFOUNDED) IS THE IMPORTANT FACTOR IN DETERMINING WHETHER THE BABY IS MALE OR FEMALE. THIS IS ACKNOWLEDGED IN THE PUBLISHED PAPER, BUT OF COURSE, LESS REPORTED BY THE MEDIA.
-Do you think lack of nutrition is affecting the thickness of cervical fluids in women and thus making it harder for Y chromosome sperm to reach the egg? What are the possible reasons for the results?
SEVERAL FACTORS, NOT JUST CALORIE INTAKE WERE ASSOCIATED WITH HAVING A BOY. SO, FOR EXAMPLE, HIGHER INTAKES OF SODIUM AND POTASSIUM WERE ALSO LINKED WITH MALE BABIES. THERE HAVE BEEN PAPERS SUGGESTING THAT ALTERATIONS IN THE INTAKE OF THESE NUTRIENTS CAN AFFECT THE pH OF THE UTERUS AND VAGINA, MAKING IT MORE ALKALINE AND HENCE MORE FAVOURABLE TO THE SURVIVAL OF Y BEARING SPERM. UNFORTUNATELY, WHETHER THIS IS ACTUALLY TRUE IS UNCLEAR. RECENT WORK (ALBEIT IN MICE – SO AGAIN WE MUST BE CAUTIOUS IN OUR INTERPRETATION) SUGGESTS THAT ALTERING THE pH OF THE UTERUS DOES NOT AFFECT THE PROBABILITY OF MALE OR FEMALE OFFSPRING.
-Is there a possibility that this is just a statistical anomaly or are
you confident in the results?
THE RESULTS ARE HIGHLY UNLIKELY TO HAVE OCCURRED BY CHANCE. THIS WAS SOMETHING FORMALLY TESTED IN THE ANALYSES (FOR ENERGY, WE WOULD EXPECT A CHANCE RESULT AS BIG OF THIS LESS THAN ONE TIME IN 200 IF WE WERE TO REPEAT THE STUDY OVER AND OVER AGAIN; FOR BREAKFAST CEREAL LESS THAN 4 TIMES IN 1000).
-Did it matter what the mothers actually ate for breakfast and their meals or were only calories measured?
I FOUND THAT EATING BREAKFAST CEREAL WAS AN IMPORTANT FACTOR. I DIDN’T ASK MOTHERS SPECIFICALLY ABOUT ‘BREAKFAST’ AS OPPOSED TO FOOD EATEN AT OTHER TIMES OF THE DAY, SO WAS UNABLE TO DISTINGUISH THE EFFECT OF EATING CEREAL (AT ANY TIME OF DAY) AS OPPOSED TO EATING SOMETHING RATHER THAN NOTHIGN FOR BREAKFAST. AGAIN, THIS WAS DESCRIBED IN THE PAPER, BUT WAS NOT OFTEN PICKED UP BY THE MEDIA.
-Could other factors possibly be interfering with the data?
I THINK IT UNLIKELY. PARTICULARLY SINCE THE WOMEN WERE A REPRESENTATIVE GROUP OF ALL THOSE LIVING IN THE TARGET AREA (PORTSMOUTH) AT THE TIME – THEY WEREN’T SOME STRANGE SUBGROUP. ALSO NONE KNEW THE SEX OF THEIR BABY AT THE TIME THEY GAVE THE INFORMATION, SO THERE COULDN’T HAVE BEEN DIFFERENTIAL OVER-REPORTING BY MOTHERS OF BOYS.
-Did you split the women into three equal groups or were there significantly less mothers who had a low energy diet?
ENERGY HAD A LINEAR RELATIONSHIP WITH THE PROBABILITY OF HAVING A BOY (IE THE MORE ENERGY, THE MORE LIKELY TO HAVE A BOY). FOR THE PURPOSES OF ILLUSTRATION THE WOMEN WERE SPLIT INTO THREE EQUALLY SIZED GROUPS. THIS MEANT THAT I COULD THEN SIMPLY REPORT THE PROPORTION OF BOYS BORN IN EACH GROUP, RATHER THAN RESORT TO USING ODDS RATIOS (EG 1.5 TIMES THE CHANCE) WHICH MOST PEOPLE DON’T UNDERSTAND.
-Why did you focus on diet in early pregnancy? Isn’t the gender decided upon fertilization? Wouldn’t “morning sickness” change the eating habits of many of the women?
I MEASURED DIET BEFORE PREGNANCY, IN EARLY PREGNANCY AND IN LATER PREGNANCY. IT WAS THE PRE-PREGNANCY DIET THAT WAS IMPORTANT.
What will you be working on after this?
I WOULD LIKE TO LOOK AT THE EFFECTS OF PATERNAL DIET ON THE SEX RATIO OF SPERM; AND ALSO TO TRY TO RESOLVE THE MECHANISM FOR THE EFFECTS I’VE SEEN.
Thanks to Fiona for taking the time to answer my questions. Her study was quite popular with the media, so I’m fortunate to receive a response so quickly. Keep up the great work scientists!
*UPDATES* A new study indicates that pregnant mothers who eat a high fat diet may have children with an early onset of puberty. Another study on sheep indicates that pregnant ewes who eat a diet high in polyunsaturated omega 6 fatty acids are far more likely to have males.