Nobody disputes that what a woman eats in pregnancy can affect her baby. But
research shows that mothers who want to give their offspring the best chance
in life need to start preparing long before the bump appears. There is
growing evidence that how young women eat and behave can affect the health
of any children they go on to have – and possibly the health of future
generations, too.
It is widely agreed that the nutritional status of a woman when she conceives
is as important as her diet in pregnancy. So it is worrying to learn that
many adolescent girls are deficient in essential nutrients including
potassium, magnesium, calcium, zinc and iron. A junk-food diet low in dairy
and fresh produce could be detrimental not just to this generation but to
their children and grand-children, too.
“A baby’s health is determined by the ability of the mother to support her
pregnancy nutritionally, which in turn is determined by her nutritional
status at the time she conceives and in the period leading up to
conception,” says Professor Alan Jackson, of the Institute of Human
Nutrition at the University of Southampton.
“The diet and nutritional status of young women of childbearing age is among
the worst in the population, and the impact of this has been seriously
underestimated. We need to focus more on diet throughout childhood and
adolescence so that a woman can take on the considerable challenges imposed
by pregnancy. By the time the pregnancy is established, the effect of making
dietary changes is much smaller than if they had been introduced beforehand.
In general, the earlier you start the better.”
The National Diet and Nutrition Survey of young people, published in 2000,
paints a gloomy picture of the female adolescent diet, revealing that girls
drink 60 per cent more fizzy drinks than milk and eat more than four times
(by weight) more sweets and chocolates than leafy vegetables. A significant
proportion of young people have very low levels of some minerals, with half
of all girls aged 15 to 18 deficient in iron and 19 per cent deficient in
calcium. One youngster in five aged 11 to 18 has poor riboflavin (vitamin
B2) status and one in eight low vitamin D status.
“Because we lead more sedentary lives and don’t need as many calories, we are
at risk of not getting the micronutrients that we need from our diet –
especially when we eat fast foods,” says Professor Sue Fairweather-Tait,
head of the micronutrients programme at the Institute of Food Research. “The
nutritional status of young women is extremely worrying. We need animal and
plant foods that have a higher concentration of micronutrients.”
Mothers-to-be who are anaemic risk having a low birth weight baby with
inadequate iron stores of its own. “Women should go into pregnancy with full
stores of iron so that they can maintain the pregnancy without taking iron
tablets, which are not always well tolerated,” says Professor
Fairweather-Tait.
Pregnant women who are deficient in calcium and vitamin D may compromise the
bone development of their babies. “A recent study found that poor maternal
vitamin D status was associated with reduced bone mass in their offspring at
age 9 and may also increase those children’s risk of osteoporosis in later
life,” says Claire Williamson of the British Nutrition Foundation, who has
also written a paper on nutrition in pregnancy. “If calcium intakes were low
during childhood and early adolescence, stores may be insufficient to meet
both maternal and foetal needs.”
Medical wisdom has long held that taking folic acid supplements in pregnancy
reduces the risk of neural tube defects, including spina bifida. But the
message emerging from research is that women who wait until pregnancy to
improve their diet may be leaving it too late. “A recent study emphasises
the importance of folic acid supplementation before the time of conception,
as once pregnancy is established it is probably too late for folic acid to
have a protective effect,” says Williamson.
“It is now well established that maternal nutritional status at the time of
conception is an important determinant of embryonic and foetal growth. The
embryo is most vulnerable to the effects of poor maternal diet during the
first few weeks of development, often before pregnancy has been confirmed.
Cell differentiation is most rapid at this time and any abnormalities in
cell division cannot be corrected at a later stage.”
It is 15 years since Professor David Barker developed the now widely accepted
Barker Hypothesis that low birth-weight babies have an increased propensity
to heart disease in later life, the greatest risk being to those who are
born small for dates, gain weight quickly and become heavy adults. Since
then it has been shown that both low and high birth-weight babies are at
increased risk not only of cardiovascular disease but of diabetes, high
blood pressure and breast cancer.
“We don’t fully understand what influences birth weight, but studies with
identical twins have shown that it is not exclusively dependent on genetic
factors, and rodent models suggest that maternal diet plays a role,” says Dr
Susan Ozanne, a lecturer in clinical biochemistry at Cambridge University.
“For example, the offspring of women who are deficient in certain specific
proteins during pregnancy are more likely to have small babies who are
consequently at increased risk of diabetes in later life.”
The weight of the mother is also crucial. Mothers who are underweight before
and during pregnancy are at increased risk of having a low birth-weight
baby, while being overweight or obese brings a higher risk of pregnancy
complications, congenital defects and other problems. Because rapid weight
gain and weight loss are both inadvisable in pregnancy, women should aim to
achieve a body mass index of 20 to 25 well before they conceive.
“Children born to obese mothers are more likely to be obese,” says Dr Penny
Gibson, adviser on obesity to the Royal College of Paediatrics and Child
Health. “So the cycle continues unless it is broken.” Similarly, mothers who
were born small are more likely to have underweight babies.
New work with animals is shedding fresh light on the trans-generational nature
of disease. While it was once thought that our health depended only on a
combination of genetic inheritance and environment, scientists are realising
that there is a third sphere of influence: the way our ancestors behaved.
This fast-growing field, known as epigenetics, focuses on the ways in which
environmental effects can change the expression of a specific gene without
altering the gene itself.
“We used to think that DNA was immutable but now we realise that it can be
modified,” says Andrew Prentice, professor of international nutrition at the
School of Hygiene and Tropical Medicine. “There seem to be various critical
windows. One of these is in the very early stages of pregnancy, but others
occur later and even after birth. And although the main emphasis has been on
mothers, the health of the sperm should not be overlooked.”
An American rat study published last year in The Journal of Physiology showed
that the “grandchildren” of animals fed an inadequate diet during pregnancy
or lactation were more likely to become obese or resistant to insulin than
those of animals fed an adequate diet. Curiously, malnourishment during
pregnancy affected “granddaughters” more severely, while malnourishment
during lactation appeared to have a greater effect on “grandsons”.
Dr Ozanne, who is doing similar work in Cambridge, says: “We know that the
female offspring of rats whose mothers had a low-pro-tein diet in pregnancy
are at increased risk of diabetes, even if the offspring have been fed a
normal diet.
“It is too early to say whether the epigenetic effect is the same in human
beings. But early studies of the offspring of parents who starved in Holland
at the end of the Second World War show that not only are they at increased
risk of obesity, diabetes and cancer, but their own children may have
inherited the risk.”
Dr Nigel Belshaw, a molecular biologist at the Institute of Food Research,
says: “It was thought that you could inherit only genes, but there also
seems to be some kind of cellular memory of what our grandmothers ate. We
don’t yet know what the implications of this are, but we need to understand
it for our futures.”
A further intriguing and unexpected twist in this tale of how one generation’s
“sins” can haunt the next came in a paper presented to the American Society
for Reproductive Medicine conference last year which suggested that women
undergoing IVF who had been born to older mothers were less likely to become
pregnant than those with younger mothers.
The implications of this research are that it is not only diet but other
aspects of behaviour that can have repercussions for future generations. It
is thought that the deterioration in the quality of a woman’s eggs caused by
ageing could be somehow transmitted to the cells that eventually become her
daughter’s eggs.
“This study involved women having fertility treatment,” says the report’s
author, Dr Zsolt Peter Nagy, of the Reproductive Biology Associates clinic
in Atlanta.
“The really big question is whether this finding can be extrapolated to the
general population. Will fertile women delaying childbirth lead to increased
problems in getting pregnant for their daughters?”
What to eat
Calcium: Soya milk and orange juice fortified with calcium; canned
anchovies; sesame seeds; tofu.
Vitamin D: Eggs and oily fish (two servings weekly). Teenage girls up
to 18 need 800mg of calcium daily and from 19 need 700mg daily. 50mg of
sesame seeds provides 330mg and a yoghurt provides 150mg.
Iron: Lean red meat, iron-fortified breakfast cereals, dried apricots
and dark green vegetables. Teenage girls and women need 15mg daily. A
typical 150g steak has 3mg; a bowl of bran flakes has 10mg, 50g of apricots
has 1.6mg.
Zinc: Wheatgerm, pumpkin seeds, canned crab and sardines are good for
zinc. Teenagers and women need 7mg daily. Wheatgerm gives half of this in a
heaped tablespoon.
Omega3 oils: Aim for 1g of omega3 oils daily. It is best to get these
from omega-3-fortified foods including breads, eggs and orange juice.
Walnuts and almonds, hemp and pumpkin seeds are also rich in omega3.
Folic acid: In addition to taking a 400 microgram supplement each day
preconceptually, eat folic acid-rich foods such as fortified breakfast
cereals (125mcg per 50g serving); black-eyed beans; Brussels sprouts; and
dark green vegetables.
What to avoid
Fatty cuts of meat: Dioxins and their related compounds are
contaminants released into our environment from industrial waste that
accumulate in our food chain in fat-rich foods; they are capable of
disrupting hormones and potentially causing birth defects.
The Food Standards Agency (FSA) advises women of childbearing age to eat no
more than two servings of oily fish a week. Salmon, sardines, pilchards,
anchovies and mackerel also contain dioxin residues. Swordfish, blue marlin,
albacore tuna and shark all contain high levels of mercury and should be
avoided.
Liver and liver pâtés: These are high in vitamin A, too much
of which can cause birth defects.
Amanda Ursell www.amandaursell.com
