KUALA LUMPUR: Lactose intolerance is a common gastrointestinal condition caused by the inability to digest and absorb dietary lactose, says Sunway Medical Centre (SMC) Paediatric Gastroenterology and Hepatology consultant Dr Ong Sik Yong.

Lactose is the main carbohydrate in human breast milk as well as cow's milk and it is also present in many other dairy products such as cheese and yogurt.

In a statement, he said the lactose that is ingested by humans needs to be broken down through hydrolysis by the lactase that is bound to the small intestine membrane before it is absorbed.

He said if a baby starts experiencing diarrhoea, constant crying and restlessness, as well as a loss of appetite after milk feeding, parents will need to be wary as the child may be suffering from lactose intolerance.

"For young infants, they actually do not absorb all of the ingested lactose from breast milk (physiological lactose malabsorption). This malabsorbed lactose is then fermented in the colon into short-chain fatty acids, hydrogen, carbon dioxide and methane. It is also converted into lactic acid by enteric bacteria (Streptococcus lactis and others) and becomes prebiotic in our gut," he said.

The increased counts of Bigidobacteria (good gut bacteria) and increased concentration of short-chain fatty acids provide considerable protective effects on colonic mucosal integrity and are beneficial for early immune development.

"Newborn infants naturally express sufficient lactase to digest about one litre of breast milk daily, and in many populations, lactase levels will decline after the weaning period (also known as lactase non-persistence). Approximately 70 per cent of the world population is affected by lactase non-persistence, which causes the condition of primary lactose intolerance," Dr Ong said, adding that in general, primary lactose intolerance did not manifest in children before five years of age.

Furthermore, lactose intolerance in young children is said to be typically caused by underlying gut conditions such as gut infection, cow's milk allergy, celiac disease or inflammatory bowel disease.

It is also mostly transient and improves with resolution of the underlying gut pathology.

According to a study, the estimated prevalence figures for primary lactose intolerance due to lactase non-persistence are two to five per cent in Northern Europe (Scandinavia, Germany and Great Britain), 17 per cent in Finland and Northern France, about 50 per cent in South America and Africa, while Southeast Asia charts between 90 and 100 per cent.

He said children with lactose intolerance have one or more intestinal or extraintestinal symptoms upon consumption of food containing lactose, including developing abdominal discomfort, bloating, farting, and/or diarrhoea. Usually, symptoms begin about 30 minutes to two hours after consumption.

Their stools would also have low faecal pH (less than 5.5) and may cause perianal skin irritation and excoriation (raw irritated lesions on skin surrounding the anus).

Such incidences usually happen after an episode of acute gastroenteritis, when a child transiently loses the ability to digest lactose. However, in most circumstances, a baby can continue breastfeeding.

"Only when there are symptoms that are progressive or troublesome such as perianal excoriation, the child may need to temporarily stop breastfeeding, but the mother can continue to express breastmilk to maintain lactation.

"Babies with transient lactose intolerance can be given lactose-free formula or soy formula for one to two weeks until the child recovers," Dr Ong added.

As for primary lactose intolerance in children, this condition usually only happens after the child turns five years old, but it can also be present as early as two years old.

When this happens, the symptoms can only be managed by limiting lactose in their diet. Thus, parents are advised to keep a vigilant eye on their child's dietary needs.

Children showing signs of lactose intolerance should only be fed dairy products with naturally lower lactose content and after a period of limiting food with lactose, the child can consume small amounts of food and drinks containing lactose.

"Children with lactose intolerance may have a little dairy product in their diet as milk and other various dairy products are a major source of calcium and vitamin D.

"Hence, it is important to make sure children who have limited dairy product intake have other non-dairy foods which are rich in these nutrients, like fish with soft edible bones (i.e. salmon and sardines) as well as green leafy vegetables. They may also require calcium or vitamin D supplements for their growing bones," Dr Ong said.

-- BERNAMA