The gut wall provides the ultimate border between self and non-self. The gut wall comprises several cell types with various functions. A mucus layer is placed above the gut wall. The mucus layer forms a highly regulated and complex barrier that is expected to allow access of water and nutrients, while protecting the infant’s body from absorbing potential pathogens.
Bacterial colonization of the gut is initiated immediately after birth. The naïve gut learns to establish a balance between commensal bacterial tolerance and well-controlled inflammatory responses to potential pathogens, during the period until around two years of age. This is called tolerance.
Tolerance can be delayed or undeveloped. Allergic responses to diet are examples, where tolerance is not fully developed and are induced by ingestion of lactose and milk protein, also called lactose intolerance and milk protein allergy, respectively.
Lactose intolerance can have different origins, and, despite intolerance, varying levels of lactose are often tolerated. Lactose intolerance is not that common in Denmark and northern European countries and actual lactose allergy is rare. Lactose intolerance, however, is extremely common in Asian countries. Focus on this issue is increasing, in general. Milk protein allergy is the most common allergy in infants and young children that affects 2-3% of this population.
Lactose is a natural part of whole milk products, including human breastmilk and cow’s milk. Lactose intolerance is present when the infant produces little or no lactase in the small intestine. Lactase is the enzyme needed for digestion of lactose. Undigested lactose will enter the colon and serve as substrate for fermentation by bacteria. Fermentation products include gases to cause clinical symptoms.
Clinical symptoms include one or more of for instance stomach-ache, abdominal bloating, diarrhoea and nausea. Clinical symptoms can cause impaired growth and failure to thrive if persistent without treatment. Feeding the infant, a lactose free diet or leaving out lactose from the diet of the lactating mother, is the treatment of choice. The aim of the treatment is to provide enough nutrition to infants suffering from lactose intolerance and ensure their ability to grow and thrive. Avoiding lactose will prevent malabsorption and fermentation of undigested lactose with appearance of related clinical symptoms.
Normal break down of proteins, into smaller peptides and amino acids, is needed for their absorption in the intestine. An infant may present with milk protein allergy, if the capacity to break down proteins is not fully developed, or not present due to other underlying circumstances. Clinical symptoms include for instance stomach-ache, constipation, dermatitis and failure to thrive.
Infants that are truly allergic to milk protein, will benefit from infant formula with fully hydrolysed proteins. Infant formula with extensively hydrolysed proteins provides an alternative to standard cow’s milk infant formula. The recommendation for infants with cow’s milk allergy, or in risk of developing this type of allergy, is to be breastfed. Milk protein allergy is extremely rare in breastfed infants. Partially hydrolysed infant formulas are meant for infants that are in risk of developing milk protein allergy. Partially hydrolysed formulas are not intended for infants with cow’s milk allergy.
At risk refers to parents or siblings being allergic and may also relate to risk of autoimmune diseases. The benefit of feeding infants, at risk of developing milk protein allergy, with partly hydrolysed protein is to avoid development of illness and needs for specialised medical nutrition.