Fourteen percent of U.S. preschoolers are overweight. This fact alone points to perhaps the strongest evidence for the effects of fetal programming.
Multiple studies have shown that either underfeeding or overfeeding the fetus during pregnancy can affect how a child's body will respond to food over a lifetime, increasing the risk for diabetes, heart disease and hypertension.
Pioneering research in the late 1980s by British physician David Barker showed that babies weighing 6 pounds or less are more likely to have an increased risk for heart disease, Type 2 diabetes and hypertension. It is the disparity between the prenatal environment and the nutritional environment after birth that appears to cause abnormalities in energy metabolism, endocrine functions and organ development.
Given the modern environment of preschoolers in Western countries -- marked by a lack of exercise, and diets high in calories, fat and sugar -- this disparity creates a problem, Barker and other researchers say.
"The fetus is reading the environment during development and is using that to predict what the environment will be once it's born," says Jerry Heindel, a fetal-programming expert at the National Institute of Environmental Health Sciences. "If the fetus gets poor nutrition, it will set itself up to be able to adjust to that. If it has poor nutrition during life, it will do quite well. But later in life, if nutrition changes and becomes like the food we're eating today, that is a mismatch, and that will increase the susceptibility to disease."
At a recent nutrition conference in Boston sponsored by Tufts University's Friedman School of Nutrition Science and Policy, the audience of nutritionists and nutrition researchers is rapt as Barker elaborates on this provocative message: Attempts to prevent such common chronic diseases as heart disease, stroke, high blood pressure and diabetes have largely failed because the origins of such diseases most likely begin in the womb.
"We were hoping and praying that we could fix chronic illness by fixing the diets of middle-age people," says Barker, an epidemiologist at the University of Southampton, United Kingdom, and Oregon Health & Science University. "But if we want to arrest the epidemic of chronic disease, we need to start early in life."
The idea has been slow to catch on.
"In other fields where people study butterflies, turtles and frogs, they have known for a long time that fetal development is very plastic and that any type of stress in the environment can cause a different phenotype in the animal," Heindel says. "In humans, people thought it was just genetics. But humans are just like these other animals." Today, U.S. doctors are primarily concerned about excessive weight gain during pregnancy. That too appears to program a fetus for metabolic problems later in life.
Exposure to a high level of blood sugar or fat before birth can change the development of fat cells and the pathways in the brain that regulate appetite, says Beverly Muhlhausler, a researcher at the University of South Australia's Early Origins of Adult Health Laboratory and an authority on fetal diet and adult disease.
"What research is now showing is that consuming an excessive amount of high-fat, high-sugar foods during pregnancy can alter the development of the baby in such a way that predisposes that individual to becoming obese later in life," she says.
Scientists from Kaiser Permanente's Center for Health Research recently found that children of pregnant women untreated for high levels of blood sugar were 89% more likely to be overweight and 82% more likely to be obese by the time they were ages 5 to 7 compared with children born to women who had normal blood sugar levels during pregnancy. The study was published last month in Diabetes Care.
One of Muhlhausler's studies in sheep found that fat cells in fetal sheep whose mothers had been fed a high number of calories during late pregnancy produced natural substances that promoted fat storage.
Further, a mother's diet may also cause changes in the fetal brain that later influence appetite and food preference.
"These individuals are less able to switch off their appetite and stop eating even when they've consumed enough calories. And this also makes them more prone to weight gain," she says. A similar study in August in the British Journal of Nutrition found that pregnant rats fed a diet of processed junk food subsequently gave birth to baby rats that also preferred junk food.
"There is so much emphasis put on a child's eating habits at school, but research is telling us more and more that the pathway to obesity can start long before the child gets to school age," Muhlhausler says. "One of my dreams as a researcher is to be able to get the message out that what you eat during pregnancy has a huge impact on your child's development and long-term health prospects."