When the body does not produce enough lactase enzymes to digest the amount of lactose consumed, undigested lactose remains in the gut. This lactose is fermented by natural bacteria, causing a build up of hydrogen and lactic acid in the gut, and increasing the passage of water through the gut wall. This process leads to the common symptoms of bloating, excess wind or flatulence, abdominal discomfort, and diarrhoea.
The severity of symptoms depends on the level of lactase enzymes produced in the body and the amount of lactose consumed. People with very low levels of lactase enzymes may react to trace amounts of lactose such as the coating on a pill, while others may be able to tolerate reasonable amounts of dairy before showing symptoms.
Symptoms usually develop about 20 minutes to 2 hours after consuming lactose, but may be delayed as the amount of undigested lactose in the gut accumulates.
It is extremely rare for lactase enzymes to be totally absent from the body – most people produce some enzymes so can tolerate small amounts of dairy. However, intake beyond this threshold causes symptoms.
Symptoms in Babies
Babies whose diets are based on breast milk or cow’s milk formula may suffer nearly continuous symptoms. Breast milk has a higher concentration of lactose then cow’s milk.
It is common for baby’s symptoms to appear worse in the late afternoon and evening as a result of the build up of gases and lactic acid during the day.
Lactose intolerance should be suspected in babies that show the following symptoms:
- Excess wind/flatulence
- Bloated abdomen
- Irritability and excessive crying
- Green, frothy stools or explosive diarrhoea
- Stomach pain, which may be indicated by a drawing up of the legs.