Lesson 3: Carbohydrates
3.2 Other carbohydrates
Lactose is the main carbohydrate in human milk. Lactase is the enzyme responsible for lactose break down (into glucose and galactose) in the intestine. Lactase activity at 26 to 34 weeks of GA has been shown to be 70% lower compared to full term infants (Antonowicz & Lebenthal 1977). This decreased lactase activity in preterm infants, may contribute to feeding intolerance (Shulman et al. 2005). Therefore, most preterm infant formulas have been developed to contain decreased lactose content. Preterm formula with low levels of lactose are less likely to cause feeding difficulties, such as gastric residuals, leading to total enteral feeding in a shorter period of time (Griffin & Hansen 1999).
Galactose is a monosaccharide released by the hydrolysis of lactose. Galactose metabolism through the Leloir pathway in the liver converts galactose to glucose, either for storage as glycogen or for energy expenditure (Hay et al. 2014).
Inositol is a carbohydrate that is found widely throughout human tissues either in its free form (phospholipid phosphatidylinositol) or in cell membranes, as phosphoinositide (Dawson & Freinkel 1961). Inositol seems to be an essential nutrient in fetal and early neonatal life. In the neonate, inositol is particularly important for neurodevelopment and for pulmonary surfactant phospholipid production and maturation. Inositol is readily available in human breast milk in relatively large concentrations (around 1,200µmol/l) (Hay et al. 2014) and it can also be endogenously produced from D-glucose. A recent Cochrane review from randomized control trials (RCT) assessed the effects of inositol supplementation in preterm infants. They found that inositol supplementation was linked to an important reduction in the rates of neonatal and infant deaths; intraventricular haemorrhage (IVH) grades 3 or 4, and retinopathy of prematurity (ROP) stage 3 or higher. An ongoing large RCT to test the benefits of routinely inositol supplementation for the preterm infant is currently on the way (Howlett et al. 2015).
Mannose is another carbohydrate present in the human milk. Although its free concentration is lower than inositol (around 40µmol/l), the total mannose concentration may be higher, as it is also present in the form of oligosaccharides. Mannose is also important in fetal neurodevelopment and it is crucial for protein glycosylation (Hay et al. 2014).
References:
Koletzko et al. 2014b
Adams & Fernandes 2014