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Building a baby: maternal diet

The phrase ‘eating for two’ is often used when talking about the diet of pregnant women. But how can the mother’s diet determine her child’s future health? Jennifer Trent Staves investigates.

Dieticians and nutritionists have long espoused the connections between a mother's diet being full of fresh food and a long, healthy life for her baby. Indeed, as I neared the end of my second trimester, my midwife gave me a claim form for £190, the ‘Health in Pregnancy Grant’, which is given to all expectant mothers once they have reached 25 weeks of pregnancy.

The idea, as presented on the marketing around the scheme, is that it should be spent on fresh fruit and vegetables to give the baby the best start possible. But is this just common sense, or is there research evidence about what a pregnant mother should be eating to best provide for her baby, and how a mother's diet affects her child? I asked a range of researchers in the field for their views.

Nutritional building blocks

The first person I arranged to speak to was Professor Caroline Fall, a Wellcome Trust Principal Research Fellow in the field of maternal health. Based in Southampton, Professor Fall first began working on maternal health during her PhD with Professor David Barker, finding a link between low birth weight and type 2 diabetes. Since then, she's focused her work on maternal diet, and today her research is primarily based in India, where undernutrition is a critical problem as mothers are not getting enough of critical vitamins and nutrients for their baby's development.

Getting enough of specific nutrients during pregnancy is critical, she explains: "There are certain parts of us that develop while we are in the uterus and do not develop further - we have almost our full complement of cells in the brain, kidneys and pancreas once we are born. If you don't have the nutrition during pregnancy to construct those tissues to the top quality, there's no going back to that stage of development and certain parts are irretrievable."

Even so, the link between maternal and child health is an indirect one, she points out. "I think some people think the mother drops food into her mouth and it drops directly into the baby's mouth, but there are a lot of things that go in between." These factors include the mother's absorption of food as well as the quality of her cardiovascular system around the uterus.

Watch a video in which Professor Fall explains more to me about the link between my diet and my baby's health

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Running time: 4 min 50 s
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Time to eat

When, exactly, during pregnancy, is it most important to be eating well? Clues that it is the very earliest stages - and perhaps even before conception - that are the most important are emerging from cohort studies where the lifestyle health of thousands of people are being followed for many years.

One such study, the Southampton Women’s Survey (part of the Medical Research Council Epidemiology Resource Centre), recruited women even before they were pregnant. "We have found that low vitamin D levels during pregnancy are linked to later bone health in children," Professor Hazel Inskip, the study's coordinator, tells me. Lower bone and mineral density has been recorded at birth and four years of age, as well as at age nine in an earlier study conducted at the centre with a smaller cohort of pregnant women. "This may not be a risk for the child at the time, but there's a long-term risk of osteoporosis in later life."

Another study is the Avon Longitudinal Study of Parents and Children, a long-term research project that's been running in the Bristol area since 1991, when over 14 000 pregnant mothers were recruited. When researchers looked for links between maternal diet at 32 weeks and the child's height and blood pressure at 7.5 years, they found little correlation.

I asked Sam Leary, a statistician and the first author on the research, why she thought there were no connections. "We measured diet at 32 weeks gestation - it may be that it's too late. Earlier pregnancy, say first trimester, may have more of an impact on what happens later. Or it could be that the children are too young; it might be that as they get older, the effects of diet do emerge."

Empty calories

While many mothers try to eat well during pregnancy, they don't always succeed. So what does a diet of unhealthy food do to a growing fetus? To find out, Dr Stephanie Bayol and colleagues at the London Veterinary College have been looking at the effects of diet on rats who are pregnant or lactating. In their study, they fed pregnant rats a diet of standard lab feed, or a diet of 'junk food' - dense in energy, highly processed, containing high amounts of fat, sugar and/or salt and refined ingredients, and often lacking essential vitamins and nutrients. The offspring were then offered the junk food diet after weaning as well.

"By the end of adolescence, the pups born to junk-food-fed mothers were overweight, overeating and developed a greater taste for junk food," she tells me. These rats ate more calories, and had abnormal levels of fat and insulin and excess cholesterol. "This is striking because these factors are linked to type II diabetes and heart disease in later life; to see an increase in those parameters by the end of adolescence is quite scary."

Watch a video of Dr Bayol showing me the effects of the mother rat's diet on the baby

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Running time: 4 min 45 s
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Diet and DNA

In 2003, researchers made the startling discovery that they could change the coat colour of baby mice simply by feeding their mothers common nutritional supplements. The mechanism, they found, was 'epigenetic' - the nutrients altered the binding of molecules to DNA (a process known as DNA methylation) that controls whether genes are switched on or off. In this case, the activity of a coat colour gene was changed, but the finding suggested how the food that a mother eats influences a baby's gene activity in later life.

"We want to see whether what's been seen in mice is happening in humans as well," says Dr Branwen Hennig at the MRC International Nutrition Group based at the London School of Hygiene and Tropical Medicine. Her team is working with pregnant women in the Gambia (West Africa), looking at their diets and their offspring from the perspective of epigenetics. The types and amounts of food eaten there vary depending on the season, as does the amount of energy that people use up.

Previous studies in the Gambia have found that the seasons affect the patterns of pregnancy. "There are more conceptions in the dry season than there are in the wet season, because the women eat the freshly harvested food and work less in the fields," Hennig tells me.

As the study evolves, the team will be able to compare data on the women's diets and the vitamin levels in food and maternal blood, as well as DNA from the babies after they are born. Their expectation is that they will find that the methylation of the babies' DNA varies depending on the season when they were conceived and what the mother was eating.

The team hopes this work, if successful, will establish a developmental principle that, in humans, what we eat especially in the early stages of pregnancy can affect our offspring's genes.

Digesting the research

Research is beginning to explain how maternal diet explains a baby's biology and health, but there is much left to discover first. For the time being, the advice for pregnant mothers is 'common sense'.

But all of the researchers I spoke to agree that the £190 grant comes very late in the developmental process. Professor Fall stresses that it's never too late, however: "We know very clearly that the pre-conceptional nutrition of the mother is very important, but it's still useful." She recommends I spend it on "fruit and vegetables - no question, as they give you a lot of the vitamins and minerals that you can't find in other foods easily."

But filling up on fruit and vegetables early in the pregnancy isn't the only message - the advice is as much about 'how' we eat as 'what' we eat. "Our research shows that it's about getting the messages across before women get pregnant - the patterns she sets up for eating for herself are the patterns she sets up for feeding her children," says Professor Inskip. "It may not be what people think of as 'hard science', but it's where we might make a difference."

Other recommendations I received include dark chocolate, vitamins and investing the money - and all of the options sound palatable. But to be honest, food is the last thing on my mind at the moment, given that in addition to my growing baby, heartburn has been my constant companion for the last 25 weeks.

This article is part of the online content for ‘Big Picture: Food and Diet’.

Please note that this feature was originally written in June 2010. The Health in Pregnancy Grant scheme has now been discontinued.

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