Even a small amount of fructose in breast milk is associated with increases in a baby’s body weight.
Add breast milk to the list of foods and beverages that contain fructose, a sweetener linked to health issues ranging from obesity to diabetes.

A new study by researchers at the Keck School of Medicine of USC indicates that a sugar called fructose is passed from mother to infant through breast milk. The proof–of–concept study involving 25 mothers and infants provides preliminary evidence that even fructose equivalent to the weight of a grain of rice in a full day’s serving of breast milk is associated with increased body weight, muscle and bone mineral content.

Found in fruit, processed food and soda, fructose is not a natural component of breast milk, which is still considered the gold standard diet for babies. The “secondhand sugar” is derived from a mom’s diet, said Michael Goran, lead author of the new study published in February in the journal Nutrients.

Exposing infants and children to higher amounts of sugar during growth and development can produce problems with cognitive development and learning as well as create lifelong risk for obesity, diabetes, fatty liver disease and heart disease, said Goran, founding director of the Childhood Obesity Research Center at the Keck School of Medicine.

Frappuccinos, energy drinks, cranberry juice cocktails and fructose are examples of sources of secondhand sugars. Healthy, naturally occurring sugars in breast milk include lactose, which is beneficial to infant growth and development.

“Lactose is the main source of carbohydrate energy and breast milk is very beneficial, but it’s possible that you can lose some of that beneficial effect depending on maternal diet and how that may affect the composition of breast milk,” Goran said. “Other studies have shown that fructose and artificial sweeteners are particularly damaging during critical periods of growth and development in children. We are beginning to see that any amount of fructose in breast milk is risky.”

Goran and his colleagues did not collect mothers’ dietary data for this study, so they were unable to determine if the trace amounts of fructose found in breast milk is positively associated with habitual consumption of fructose–rich foods and drinks.

“We know very little about why some children eventually become overweight or obese,” Goran said. “It’s important that we study what may be taking place in the earliest times of their development to determine whether anything could be done just after birth to lower their risks.”

The first year of life is a critical period for building brain networks and for cementing the foundation for the metabolic system. Minute amounts of fructose may have detrimental effects on infant metabolism, said Tanya Alderete, co–author of the study and a postdoctoral research scholar at the Keck School of Medicine. Ingestion of fructose could coach pre–fat storage cells to become fat cells, raising the baby’s risk of one day becoming overweight or obese.