Mother’s Milk, Formula Feeding Studied for Lasting Effects on Babies

Feeding a baby requires a fine balance. Some parents anxiously push formula or mother’s milk on a satisfied, well-fed baby. Others mistakenly assume that if skim milk is good for them, it is also good for their infant.

Mothers may one day choose a formula or opt to breast-feed in order to give their babies “just the right fats” to prevent heart disease in later life.

The idea of finding the right balance of fats makes sense, said pediatric nutritionist Cutberto Garza. Some children develop “fatty streaks” in their arteries, which he believes are the start of cholesterol deposits that eventually clog arteries in adults and cause heart attacks. Garza is associate director of the U.S. Department of Agriculture Children’s Nutrition Research Center in Houston and a pediatrician at Baylor College of Medicine.

Garza said infant nutrition research is aimed at finding the proper balance--a diet for life’s first years that permits children to develop normally without setting the stage for clogged arteries later on.

Fat, the bane of heart-healthy adulthood, actually is essential to babies’ early growth, according to experts.

“Young infants really do need the fat in breast milk or formula to grow properly. An ounce of fat contains more calories than an ounce of protein or carbohydrate. An infant needs that energy to grow,” said Dr. Joyce D. Gryboski, a pediatric gastroenterologist at Yale-New Haven Hospital, whose research has focused on digestive development. Babies need the long-chain fatty acids of breast milk for growth, energy and brain development, she said.

Pediatricians already have evidence that infants and young children who have low-fat diets early in life don’t grow properly, said Dr. William Weidman, a pediatrician at Mayo Clinic who serves on the American Heart Assn.’s nutrition committee. “It’s important that an infant or toddler not be fed low-fat or skim milk. There have been documented cases of ‘failure to thrive’ in children whose well-intentioned but misguided parents put them on the wrong kind of milk,” Weidman said.

Brain development is one important reason why babies need fat. An infant adds brain cells into the second year of life, says Sue Griffin, a developmental neurobiologist at the University of Arkansas Medical Center in Little Rock. Growing new cells requires fatty acids and cholesterol, as does the “wiring” that connects the cells for communication. Infants who drink skim milk don’t have the required fats. In fact, breast milk is the best food a baby can have for brain development, Griffin says.

Pediatricians, cardiovascular researchers and nutrition experts are now trying to pin down what kinds of fats a growing infant needs. Others are examining how many calories an infant needs to grow. This work will one day lead to dietary guidelines that may help prevent cardiovascular disease while promoting proper growth and development in children up to 2 years of age. Such guidelines don’t yet exist; the AHA currently places no restrictions on fat intake during the first two years of life.

San Antonio researchers are looking at infant diets and subsequent heart disease in baboons, primates studied for their similarity to humans. Douglas S. Lewis, associate scientist at the Southwest Foundation for Biomedical Research, has studied groups of baby baboons that were breast-fed and those raised on commercial formulas. Such formulas contain fat from coconut, soybean and safflower oils.

The researchers found that, as mature adults, the breast-fed baboons had more arterial plaque than those fed formulas. In baboons then, it is possible that breast milk might increase the susceptibility to an atherogenic diet, laying part of the foundation for adult heart disease, Lewis said, adding that extrapolation of his work to humans would be premature.

An infant’s diet may also make a big difference in his or her cholesterol levels. “Breast milk, considered a natural food, is high in cholesterol; the commercial infant formulas are 10 times lower in cholesterol. We don’t know yet what those differences may mean over the long haul,” said Dr. Ricardo Uauy, associate professor of pediatrics at the University of Texas Southwestern Medical Center, Dallas. He cares for children who have genetic diseases such as familial hypercholesterolemia, or high blood cholesterol. But even these children should be breast-fed up to six months of age. “In any case, we don’t start intervention (with the disease) before that age,” said Uauy.

“The question is: What are the lifelong effects of different fats an infant might be fed? What are the differences between cow milk’s butter fat (saturated), formula’s vegetable oil (polyunsaturated) and breast milk’s monounsaturated fats?” said Dr. L.J. Filer, a pediatric nutrition specialist at the University of Iowa Hospital. Research has shown that specific types of dietary fat do affect blood levels of cholesterol, lipids and the lipoproteins that carry both in the blood.

As early as 1981, Belgian biochemists showed that month-old infants fed a formula with polyunsaturated fats had lower levels of low-density lipoprotein (LDL) than breast-fed babies. LDL is the “bad” molecule linked with heart disease.

New Orleans researchers at Louisiana State University Medical Center, who conduct the ongoing Bogalusa Heart Study, found that average blood lipid levels increased rapidly during the first six months of life. Two-year-old infants had levels nearing those found in teen-agers and young adults.

“Our work shows that some children at increased risk for cardiovascular disease might be picked up while they are still babies,” said Sathanur R. Srinivasan, a co-author of the study and a professor of biochemistry and medicine at LSU.

Nobel Prize winners Michael S. Brown and Joseph L. Goldstein, researchers at Dallas’ Southwestern, have suggested that a high-fat diet increases cholesterol levels in the blood as a person ages.

“If we can understand why a baby’s body is able to adapt to high cholesterol intake, we may help both them and adults,” said Uauy.

Some evidence also exists that many American babies might be overfed because current caloric requirements are too high. Baylor’s Garza heads a USDA team that has spent six years studying how many calories a baby needs daily for each pound he weighs to keep growing.

“The feeding recommendations that a mother now gets from pediatricians are based, in part, on a goal of doubling the baby’s birth weight by the age of five months,” Garza said. “Current estimates are that the average baby needs 45 to 50 calories daily for each pound he weighs to reach that goal. We’ve developed some evidence that breast-fed infants need only 35 to 40 calories per pound to grow. There’s a chance bottle-fed infants are getting more calories than they need,” Garza said.

In any case, maximum growth may not be ideal, he said. Studies indicate that when animals are fed for maximal growth, they are likely to have earlier onset of chronic diseases such as heart and kidney disease and cancer.

“There isn’t any simple connection between cholesterol, serum lipids and advanced atherosclerosis. It isn’t as simple as adding two and two to get four,” said Garza. “A lot of work must be done before we have preventive recommendations for children under 2 years. Our knowledge at this point is incomplete; we have pieces of the puzzle, not the whole picture. Today, mothers should breast-feed infants whenever possible. Formula is an acceptable alternative when it is prepared properly without contamination.”

Recent work also suggests that a mother’s diet can affect the composition of her breast milk, said Uauy. Infants born to mothers whose milk has a lower fat content take longer to feed. But with time, the fat content increases and the baby gains weight more quickly and feeds faster. He said some researchers think modifying the mother’s diet may offer another way to modify infant diets--if researchers determine one day that modification is needed.