Bumpy ride: the truth behind pregnancy mythsby Listener Archive
Faced with so much conflicting advice about her baby-to-be, science journalist Linda Geddes investigated the truth behind the headlines, guidelines and old wives’ tales.
As a newly pregnant woman, I was bursting with questions about my developing child. I remember having my 12-week scan and spending the following weeks obsessing over what this prawn-shaped blob (which already showed signs of extraordinary wit and intelligence) was doing in there. Could it tell when I was in an aeroplane, taste the chicken jalfrezi I was eating at the local Indian restaurant or know that it was night-time?
I was also bemused by conflicting advice on eating, drinking and exercise, much of which seemed to fly in the face of common sense. I made it my job to indulge my curiosity and investigate the truth behind the old wives’ tales, alarming newspaper headlines and government guidelines. So my book Bumpology was born. What started as a 14-part blog for the New Scientist during the latter weeks of my first pregnancy developed into a two-and-a-half-year obsession with the science of bumps, birth and newborn babies.
Shortly after starting to write this book, I became pregnant with my second child. This time it was a very different experience. The more I researched, the more I realised that much of what I had been told during my first pregnancy was not backed up by evidence and in some cases – such as being told that if I requested epidural pain relief, I was more likely to need a C-section – was plain wrong.
I became increasingly angry. Every week, expectant parents are given new things to worry about. Bumpology is my attempt to make sense of all the conflicting advice that’s out there about pregnancy, birth and raising babies.
WHY DO PREGNANT WOMEN CRAVE UNHEALTHY FOOD?
Angelina Jolie craved chocolate with cinnamon and chilli, Cate Blanchett wanted pickles and icecream, while Britney Spears is said to have wanted to eat soil. A recent study on the pregnancy website www.babycenter.com found that about 85% of American women experienced at least one food craving during pregnancy. Around 40% craved sweet foods, and 33% lusted after salty snacks. Spicy foods came in third, at 17%, followed by fresh fruit, at 10%.
Surprisingly few scientific studies have been carried out on food cravings during pregnancy. Those that have been find that pregnant women often have a desire for salty foods and become less sensitive to the taste, as well as becoming more sensitive to bitter tastes.
The salt craving may come about because, as their blood volume expands, pregnant women need slightly more salt to maintain the balance of fluids in their bodies. An aversion to bitter flavours is less easy to explain, but some have proposed that it steers women away from poisonous plants, which are often bitter. As to why pregnant women crave sweet foods, studies of how taste preferences vary over the menstrual cycle may provide some clues. Women tend to want foods that are high in carbohydrate and fat during the second half of the menstrual cycle, when levels of the hormone progesterone are high. They are more sensitive to sweet tastes during the first half of the cycle, when levels of oestrogen are higher.
Although both hormones increase during pregnancy, there is relatively more progesterone than oestrogen, which may explain why women long for sweet, energy-rich foods like chocolate or cake (or preferably both at the same time).
A lot of people assume that you crave the foods your body needs. Although no one has specifically studied this in pregnant women, there is some evidence that it may be true. Leigh Gibson and his colleagues at the University of Roehampton, London, gave their test group two flavours of soup to try, one that was high in protein and one that was low. A few days later, the volunteers were either starved of protein or given a protein-rich drink before being offered a choice of the two soups for lunch. Those that were protein-starved said they preferred the protein-rich flavour, and they also ate far more of it. In other words, if you are starved of protein, you subconsciously begin to prefer the taste of foods that contain large amounts of it. “It seems we can rapidly learn to want to eat foods that supply needed nutrients like protein,” says Gibson.
Likewise, cravings for sweet, fatty foods may reflect a need for energy, although Gibson cautions that they could also reflect a need for emotional comfort, as we often get a lot of pleasure from eating them.
DO PREGNANT WOMEN REALLY EAT COAL?
“Have you been eating coal?” was the first thing my dad asked me upon learning I was pregnant. Strange as it sounds, some women develop a taste for minerals, metallic objects and even soil during pregnancy, a phenomenon known as “pica”. Some have proposed that it’s a sign of iron deficiency – though how much iron you’d get from a mouthful of coal is questionable.
A survey of 2231 British women found that 31% claimed to have experienced unusual cravings during pregnancy. Top of the list was ice, followed by coal, toothpaste, sponges, mud, chalk, laundry soap, matches and rubber. One of my neighbours even reported a penchant for cigarette ash during her pregnancy.
Many of these phenomena have their own names. Pagophagia, or ice-eating, is also common among American women: a separate survey found that 18% of women in the state of Georgia did it, the amount they ate ranging from a couple of glasses of ice cubes to several kilograms a day.
Earth-eating, or geophagia, is particularly common in African countries such as Tanzania, where up to 60% of pregnant women indulge. Clay-rich soil seems particularly desirable, although pottery is sometimes eaten, instead.
Scientists have proposed various explanations for pica, including cultural trends, stress relief (like biting one’s fingernails) and hunger. Some women who have been interviewed about their pica say that it helps to relieve heartburn and nausea, and often the items they choose have an alkaline pH, which may help to neutralise stomach acid. Most women, though, have no idea why they crave such oddities.
A common scientific explanation is that these women are deficient in certain nutrients, such as iron, zinc or calcium. Although there have been hundreds of reports of iron-deficient
women craving soil and other pica, when researchers have analysed how much iron is released from the digestion of soil or clay, the answer is: very little. Neither does giving women iron supplements to cure their anaemia stop their cravings. What’s more, eating clay and soil can actually inhibit the uptake of iron and other minerals by the gut. But just because soil doesn’t cure anaemia, it doesn’t mean anaemia doesn’t trigger the craving. “It may be that being deficient in essential minerals induces a craving for anything mineral-tasting,” says Gibson.
CAN UNBORN BABIES TASTE WHAT MUM IS EATING?
Unborn babies are floating in a veritable cocktail of taste sensations, which may be teaching them what’s good to eat in preparation for when they pop out into the big wide world.
Taste buds on the tongue begin to develop just 13 to 15 weeks into pregnancy, enabling babies to detect simple tastes such as sweet, sour and salty, but many of the more complex flavours we experience are the result of volatile molecules from foods like garlic passing over smell receptors in the nose.
All these things can find their way into the amniotic fluid that surrounds the baby, in much the same way that flavours also get into breast milk. “If it gets into the blood supply, it will get into the amniotic fluid and the breast milk,” says Julie Mennella at the Monell Chemical Senses Center in Philadelphia, Pennsylvania, who spends her days trying to understand how preferences for certain flavours develop.
During the third trimester of pregnancy, fetuses breathe and swallow around a litre of amniotic fluid a day – probably as practice for when they’re born, rather than for any nutrients – and much of this fluid will pass smell and taste receptors in the nose and mouth.
Some smelly molecules, such as the sulphurous compounds that give garlic its characteristic smell and taste, are so potent that if you take a sample of amniotic fluid from a woman who has eaten a garlicky meal, you can smell the garlic wafting from it.
So unborn babies do get a taste of what their mums are eating during pregnancy, and they also seem to remember it. Several studies have shown that babies whose mothers ate a lot of garlic or aniseed during pregnancy are attracted to those smells in the first days after birth, making sucking motions when they catch their scent.
CAN MUM'S FOOD FADS INFLUENCE HER BABY'S PALATE?
Not only are babies treated to a banquet of flavours before birth, but it also seems the memory of these tastes may influence the kinds of foods they like in later life.
Studies have shown that if Mum drinks a glass of carrot juice four times a week during the last trimester of pregnancy or the first two months of breastfeeding, her baby will find cereal prepared with carrot juice particularly appealing once it has been weaned. Babies whose mums eat a lot of fruit during pregnancy are also more likely to enjoy fruit during weaning. “The baby is learning what foods Mum likes,” says Mennella. “I think it’s the first way they learn what foods are safe and also what foods are available.”
Trying to eat as many different flavours as possible during pregnancy and breastfeeding should therefore expose your baby to a smorgasbord of different tastes, and in theory this may make it less prone to fussy eating. However, it could also set a bad example if you choose to indulge in less wholesome options. Babies whose mothers drank two small glasses of wine a week during pregnancy showed more smiling, suckling and licking expressions in response to the smell of alcohol than those whose mums drank very little or nothing at all – although it’s not clear whether this penchant for alcohol lasted into adulthood.
Weirdly, several studies have found that children’s appetite for salt can be influenced by the degree of morning sickness their mothers experienced. Sixteen-week- old babies whose mothers endured moderate to severe vomiting during the first 14 weeks of pregnancy were more tolerant of salty drinks than those whose mothers experienced no morning sickness. One possible explanation is that throwing up can make women dehydrated, making their amniotic fluid more concentrated and salty.
Edited extract from BUMPOLOGY: THE MYTH-BUSTING PREGNANCY BOOK FOR CURIOUS PARENTS-TO-BE, by Linda Geddes (Bantam Press, $39.99).
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