The Importance of Lactose in Breastmilk
by Anne Eglash MD, IBCLC, FABM
The article for this week’s CQW arose from a meeting of several health professionals in Mexico where they summarized the evidence on the importance of lactose in the human diet. Yes, it was supported by the dairy company FrieslandCampina, but there are interesting points about lactose in this summary that may have clinical application.
Lactose is the main sugar in mammalian milks. Human milk is higher in carbs that some other mammals, with 40% of the calories provided by lactose. Lactose is broken down in the gut into the molecules glucose and galactose by the enzyme lactase. Lactase is made by cells lining the gut, with the highest concentration in the jejunum (first part of the small intestine), and is detectable by 8 weeks of gestation.
Although preterm infants have low lactase activity, after 5 days of exposure to breastmilk, the lactase enzyme quickly rises, reaching 98% efficiency in digestion of lactose. If an infant is exposed to excessive lactose (e.g. high foremilk), the authors state that bacteria residing in the tail end of the small intestine or in the colon will ferment the lactose, creating gas, lactate and short chain fatty acids, and sometimes diarrhea.
Infants with a genetic disease called galactosemia type 1 should not ingest lactose because they cannot metabolize galactose. This is quite rare, only occurring in 1 per 16,000-60,000 infants. Lactose intolerance in infants might occur after a GI illness such as severe diarrhea, but infants typically will regain the ability to digest lactose.
The authors discuss the effect of lactose on infant metabolism and health, as well as possible consequences of using other sugars besides lactose in infant formulas. Test yourself with the question first, then read the comment to learn more.
- Lactose provides 6 calories (kcal) per gram whereas glucose provides 4 calories (kcal) per gram.
- Lactose has a higher glycemic index than glucose, which means that it raises the blood sugar higher after ingestion as compared to glucose.
- Consumption of infant formula with corn sugar has been shown to raise the insulin level higher as compared to lactose-containing formula.
- Lactose does not stimulate the reward center of the brain like glucose or fructose.
- High lactose exposure reduces the growth of Bifidobacterium, a health-promoting bacteria in the breastfed gut.
- Lactose helps aid the absorption of calcium from milk.
- Lactose is as likely to cause caries in teeth compared to sucrose (table sugar).
See the Answer
Lactose is a unique component of breast milk, many infant formulas and dairy products, and is widely used in pharmaceutical products. In spite of that, its role in human nutrition or lactose intolerance is generally not well-understood. For that reason, a 2-day-long lactose consensus meeting with health care professionals was organized in Mexico to come to a set of statements for which consensus could be gathered. Topics ranging from lactase expression to potential health benefits of lactose were introduced by experts, and that was followed by a discussion on concept statements. Interestingly, lactose does not seem to induce a neurological reward response when consumed. Although lactose digestion is optimal, it supplies galactose for liver glycogen synthesis. In infants, it cannot be ignored that lactose-derived galactose is needed for the synthesis of glycosylated macromolecules. At least beyond infancy, the low glycemic index of lactose might be metabolically beneficial. When lactase expression decreases, lactose maldigestion may lead to lactose intolerance symptoms. In infancy, the temporary replacing of lactose by other carbohydrates is only justified in case of severe intolerance symptoms. In those who show an (epi)genetic decrease or absence of lactase expression, a certain amount (for adults mostly up to 12 g per portion) of lactose can still be consumed. In these cases, lactose shows beneficial intestinal-microbiota-shaping effects. Avoiding lactose-containing products may imply a lower intake of other important nutrients, such as calcium and vitamin B12 from dairy products, as well as an increased intake of less beneficial carbohydrates.
Lactose, like all other carbs, provides 4 kcal of energy per gram. Lactose does not raise the blood sugar as high as glucose, and the galactose component does not stimulate insulin release, so that the insulin level is lower when ingesting lactose as compared to glucose.
Lactose does not stimulate the reward center of the brain, and rat studies have shown that lactose does not suppress pain as well as glucose, sucrose, or fructose.
Lactose is important in promoting the growth of bifidobacterium, which is a health-promoting bacteria in the breastfed gut. Lactose also induces the level of gastrointestinal anti-microbial peptides, helping to decrease the risk of infection. Lactose promotes more acid formation in the gut due to lactic acid, which helps absorb calcium.
Lactose is less likely to cause cavities as compared to sucrose.
The effect of using other sugars in infant formula instead of lactose is still being investigated, but there are concerns that other sugars (corn sugar, maltodextrin) may promote E Coli growth, stimulate the reward center, raise the insulin level higher, and increase the risk of cavities. The use of nonlactose sugars in the infant’s diet may therefore have long lasting effects on health.