By Peta Bee
When I was pregnant, I tried not to eat too much or too little and was careful to avoid foods that were potentially risky, but beyond that I made few changes to my regular diet. Instinct told me that obsessing about food would have negative consequences for my unborn baby, and that sticking to what my body knew was the surest way for us both to stay healthy. But should I have done more? If I had been more selective about the foods I ate when I was expecting, could I have prevented my son’s sweet tooth, for instance? Well, possibly. Some experts now believe food imprinting begins in the womb, and that mothers who eat only nutritious foods are programming their children to do the same.
In a book called Feeding Baby Green, Alan Greene, a clinical professor of pediatrics at Stanford University, says an unborn baby can acquire what he terms “nutritional intelligence” from the flavors experienced from gestation onward. Even by the second and third trimester, says Prof. Greene, the fetus develops highly sensitive tastebuds through “practice meals” of amniotic fluid that enable it to remember the taste of whatever their mother has eaten. His theory—shared by a growing number of pediatric nutritionists—is that a fetus remembers and stores this information, using it to seek out the same types of food after birth. “How a child eats is a learned behavior,” says Greene. “By starting before birth, not only can you teach them to love appropriate amounts of foods, but you can help set the trajectories of their health, intelligence, weight and metabolism.
For expectant mothers already overburdened with recommendations to avoid everything from alcohol and medications to contact with pets, and keep exercising but not too much, is Greene’s advice just another means of fueling prenatal paranoia? Pressures to feed preschool-aged children the right diet already instills panic among many mothers, and the prevailing wisdom is for pregnant women to stick with a “normal” balanced and healthy diet.
However, a nutrient-rich diet has been shown to promote a healthy birth weight in babies. A study published in the European Journal of Clinical Nutrition proved this point when a group of pregnant women who took dietary supplements gave birth to heavier babies than those in the study who didn’t.
Evidence that the diet of expectant mothers is indeed influential has mounted in recent years. It is known that strong flavors, such as vanilla, anise, garlic and onions, are transmitted through amniotic fluid in the womb and breast milk. When nutritionists at the Monell Chemical Senses Institute in Philadelphia gave expectant mothers either carrot juice or water for four days a week for three consecutive weeks during their last trimester of pregnancy, and again during the first two months of breastfeeding, they found that food preferences were greatly affected. At about six months the babies were given two bowls of cereal, one made with carrot juice, the other with water. Children who had been exposed to carrot juice, either in the womb or through breast milk, appeared to enjoy the veggie-flavored meal much more than those whose mothers had had only water.
Researchers in New Zealand showed how sedentary expectant mothers were more likely to give birth to children who became inactive themselves, and in another study, the daughters of women who ate a high-fat diet during pregnancy and nursing were likely to reach puberty much earlier than those with mothers who consumed only moderate fats. And last year a study published in the Journal of Physiology provided perhaps the strongest evidence yet that food imprinting can have a long-term effect. Pregnant and nursing rats were given either a balanced diet with healthful foods, or a diet containing large amounts of processed foods high in fat, sugar and salt. What they found was that the offspring of the animals fed only a healthy diet tended to select healthful foods in adulthood, meaning they stayed relatively slim and avoided disease. “We have always been told that ‘you are what you eat,’” says Dr. Stephanie Bayol, one of the authors of the study. “In fact, it may also be true that “you are what your mother ate.”
So is it too late to make amends after the child is born? Encouragingly, Greene says the benefits of food imprinting can continue until a child is about two and a half. If a woman eats a variety of healthy and varied foods when she is breastfeeding, for instance, her baby will be exposed to subtle changes in properties that are not present in formula milk. “Breast milk is dynamic and tailored to a specific situation,” he says. “The nutrient content changes, the flavors change, and the immune properties change to fit your baby’s changing needs.” He cites studies that show mothers of premature babies produce milk with a higher protein content than those who deliver at term.
Food-imprinting becomes critical at the weaning stage, Greene says. Giving babies processed white rice for their first solid is partly why refined carbohydrates become the centerpiece of diets in older children. Likewise, jarred baby food could leave children familiar enough with the texture and taste of processed food to develop a preference for it. During what he calls “the baby-food months,” experiencing a flavor six to ten times can provide children with a predilection for it, and “children get imprinted with processed or incredibly sweet flavors this young,” Greene says.
One exacerbating factor is that too many parents lack patience when it comes to encouraging under-twos to try new foods. “About one quarter of parents give up on a food after one or two tries if their baby seems not to like it,” Greene explains, “yet there is evidence that if a baby tries something previously spurned, after seven or eight attempts they eventually accept and like it.” But this is easier said than done when faced with a stubborn toddler who clamps up at the appearance of anything green or orange. Should we really persist when 
tantrums, tears and general household chaos are likely to erupt at every meal? In Greene’s view, it’s okay to switch as long as it’s not to a jar. “Giving children a cooked, processed jar of peaches does not translate into their opting for the fresh, raw fruit later on,” he says. “If they won’t eat a fresh peach, leave it awhile and try something else.”
Bayol and her team believe the results of their animal-based studies hold true for humans and could have huge implications for health. In their most recent investigations, the offspring of pregnant rats fed healthful foods were more likely as adults to be normal weight and have acceptable blood pressure, triglyceride and cholesterol levels than the offspring of fast-food eating mothers. A junk-food diet during pregnancy and breastfeeding was more likely to result in offspring who would overeat and develop obesity.
“None of this means that poor health is inevitable if your mother didn’t eat well, as it is still important to exercise and adopt a healthy diet yourself,” says Bayol. “But it does mean that mothers should try to eat responsibly while pregnant.”
Peta Bee is an award winning British journalist with a degree in sports science and a Masters in nutrition. An earlier version of this story appeared in The Times of London.
Photo lower right courtesy Kristen Pratt Machado
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