For a developing baby, carbohydrates represent a primary source of energy, fueling their rapid growth. While both breast milk and infant formula are designed to meet this need, the specific types of sugars they contain are a nutritional difference. This exploration will detail the sugars found in breast milk and formula, shedding light on their composition and how they function within a baby’s body.
The Natural Sugars in Breast Milk
The principal carbohydrate in human breast milk is lactose, which accounts for approximately 40% of its energy. Lactose is a disaccharide, meaning it is a sugar composed of two simpler sugar molecules, glucose and galactose. An enzyme called lactase, which all infants are born with the ability to produce, breaks down lactose into these two components for easy absorption and use as a direct energy source.
Beyond providing simple energy, breast milk contains a complex class of carbohydrates called Human Milk Oligosaccharides (HMOs). These are the third most abundant solid component in human milk, after lactose and lipids. Unlike lactose, HMOs are indigestible by the infant, meaning they are not used for energy. Instead, they travel to the large intestine, where they perform several specialized functions that support a baby’s health.
There are over 200 different types of HMOs known to exist, and their composition varies between mothers and throughout the stages of lactation. These complex sugars act as prebiotics, selectively feeding beneficial bacteria in the infant’s gut, particularly species like Bifidobacterium. This helps establish a healthy gut microbiome from birth. HMOs also support the immune system by acting as decoys; they mimic the receptors on intestinal cells that pathogens would normally bind to, effectively trapping harmful bacteria and viruses and preventing them from causing infection.
Carbohydrate Sources in Infant Formula
The goal of infant formula is to model the nutritional profile of breast milk as closely as possible, and for this reason, lactose is the preferred and primary carbohydrate used in most standard, milk-based formulas. It provides the same energy source as the lactose found in breast milk and helps with the absorption of minerals like calcium.
Some formulas, however, utilize different carbohydrate sources for specific medical or dietary needs. These alternatives are most often found in formulas designed for babies with sensitivities, such as a cow’s milk protein allergy or the rare genetic disorder of congenital lactase deficiency. In these situations, a lactose-free formula is necessary.
The most common substitutes for lactose are corn syrup solids and maltodextrin, which are sugars derived from corn starch. Corn syrup solids are created by dehydrating corn syrup, which is composed almost entirely of glucose molecules. These carbohydrates are easier to digest for infants who cannot process lactose. Sucrose, or common table sugar, is another alternative, though it is less frequently used and typically found only in certain specialty formulas.
How These Sugars Affect a Baby’s Development
The sugars in breast milk have a dual function. While lactose offers fuel, the indigestible HMOs actively shape an infant’s developing systems. By establishing a protective gut microbiota, HMOs create a microbial balance that is foundational for long-term health, influencing digestion and immune function. Their ability to block pathogens strengthens the gut barrier and helps educate the immune system.
Carbohydrates in most infant formulas, particularly those using corn syrup solids or maltodextrin, primarily serve an energetic role. These sugars are effective at providing calories for growth, but they do not offer the same multifaceted benefits as HMOs. Corn syrup solids, being composed of glucose, are metabolized differently than lactose. This leads to a higher glycemic index, which can cause a more rapid increase in blood sugar and insulin levels after feeding compared to lactose. The long-term consequences of this different metabolic response are still being studied, but some research suggests a potential link between the consumption of corn syrup solid-based formulas and a higher risk of obesity later in childhood.
Recognizing the benefits of HMOs, some formula manufacturers have begun adding prebiotics like galacto-oligosaccharides (GOS) and fructo-oligosaccharides (FOS) to their products. These are simpler, non-human oligosaccharides intended to mimic the prebiotic effect of HMOs by stimulating the growth of beneficial gut bacteria. While studies show these additives can help foster a healthier gut microbiome compared to formulas with no prebiotics, they lack the structural complexity and diversity of the hundreds of HMOs found in breast milk. Therefore, they cannot replicate the full range of protective and immune-supporting functions, such as acting as pathogen decoys, that HMOs provide.