Lactose: A key nutrient in infant nutrition

In infant nutrition, the main objective is to get as close as possible to the composition of breast milk. Thus, the simple fact that lactose is the main component of breast milk makes it an essential element whose benefits do not necessarily need to be shown to be recommended. This is why there are few studies in the literature demonstrating the benefits of lactose in infant nutrition.

Essential for infants

Lactose is the main component of breast milk, whose concentration increases with the stage of lactation: from about 40 g/L for colostrum, 65 g/L for transitional milk and 75 g/L for mature milk (1). To be digested by the body, lactose is hydrolyzed in the small intestine into glucose and galactose by an intestinal enzyme called lactase. This enzyme, lactase, is detected from the 12th week of pregnancy (2) and the greatest increase in its activity occurs in the third trimester, when its activity is multiplied by 3 or even 4 (3). After the first breastfeeding, lactase activity increases rapidly in order to digest the lactose naturally present in breast milk (4,5). Five days after starting breastfeeding, lactose hydrolysis is 98% efficient (6).

Lactase splits the lactose in two, releasing galactose and glucose for absorption and use by the body. Galactose is a monosaccharide, which means that it is composed of several glucose molecules, attached together (7). Once galactose is absorbed, it will be able to release energy (7). In addition, galactose is essential in the creation of myelin, a membrane made up of lipids and proteins surrounding nerve fibers, which increases the speed of nerve impulse transmission along these nerve fibers (7). As for glucose, it provides energy to the cells in infants (8) and is essential for the development and functioning of the newborn’s brain.

Lactose is thought to help the establishment of microbiota in infants and may protect them against infections

It is now scientifically recognized that diet plays a major role in the colonization of the intestinal microbiota, which could then impact metabolism and long-term health. It is quite clear in studies conducted in vivo on animal models and in vitro that lactose consumption impacts the composition of the gut microbiota.

A study conducted on pigs after lactation shows an increase in the amount of Lactobacili, a beneficial gut bacterium, following dietary lactose supplementation for two weeks, compared to the control group without lactose (9). Similarly, an in vitro study shows that lactose impacts bacterial populations, especially by increasing the population of Bifidobacteria (10,11). For infants allergic to cow’s milk protein, the addition of lactose (38g/L) to a formula also leads to a significant increase in the number of beneficial bacteria such as Bifidobacteria and Lactobacillus, and a significant decrease in the number of more harmful bacteria such as Bacteroides and Clostridia compared with the same formula without lactose (12). This modulation of the microbiota is associated with a modification of its activity since we observe an increase in the production of short-chain fatty acids, these molecules known for their benefits on intestinal health (10-12). Thus, lactose is a key nutrient in the colonization of the infant’s gut microbiota by promoting the establishment of beneficial bacteria.

Bibliographie

1. Saint L, Smith M, Hartmann PE. The yield and nutrient content of colostrum and milk of women from giving birth to 1 month post-partum. Br J Nutr. juill 1984;52(1):87‑95.
2. Szilagyi A. Chapter 2 – Digestion, absorption, metabolism, and physiological effects of lactose. In: Paques M, Lindner C, éditeurs. Lactose [Internet]. Academic Press; 2019 [cité 11 mars 2022]. p. 49‑111. Disponible sur: https://www.sciencedirect.com/science/article/pii/B9780128117200000027
3. Shulman RJ, Wong WW, Smith EO. Influence of changes in lactase activity and small-intestinal mucosal growth on lactose digestion and absorption in preterm infants. The American Journal of Clinical Nutrition. 1 févr 2005;81(2):472‑9.
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9. Daly K, Darby AC, Hall N, Nau A, Bravo D, Shirazi-Beechey SP. Dietary supplementation with lactose or artificial sweetener enhances swine gut Lactobacillus population abundance. Br J Nutr. juin 2014;111 Suppl 1:S30-35.
10. Natividad JM, Marsaux B, Rodenas CLG, Rytz A, Vandevijver G, Marzorati M, et al. Human Milk Oligosaccharides and Lactose Differentially Affect Infant Gut Microbiota and Intestinal Barrier In Vitro. Nutrients. 19 juin 2022;14(12):2546.
11. Van den Abbeele P, Sprenger N, Ghyselinck J, Marsaux B, Marzorati M, Rochat F. A Comparison of the In Vitro Effects of 2’Fucosyllactose and Lactose on the Composition and Activity of Gut Microbiota from Infants and Toddlers. Nutrients. 25 févr 2021;13(3):726.
12. Francavilla R, Calasso M, Calace L, Siragusa S, Ndagijimana M, Vernocchi P, et al. Effect of lactose on gut microbiota and metabolome of infants with cow’s milk allergy. Pediatr Allergy Immunol. août 2012;23(5):420‑7.

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