Allergic reactions to foods can be life-threatening. Mind Your Body talks to experts about different food allergies and intolerances

One man’s meat is another man’s poison, goes the adage.

When it comes to food allergies, what can be eaten and enjoyed by one person may cause unwanted – and sometimes life-threatening – symptoms in another.

However, food intolerances and food allergies are very different.

Food intolerance is an adverse reaction to certain foods or food components that typically occur each time they are eaten.

Typically, intestinal symptoms like abdominal pain and discomfort, diarrhoea and vomiting will occur.

Food allergy is more severe as it involves the immune system, said Dr Law Ngai Moh, a specialist in gastroenterology at Raffles Hospital.

It occurs when the immune system mistakes a harmless food for a dangerous invader. It then produces antibodies to fight the food.

In addition to intestinal symptoms, reactions to food allergies include rashes, swollen lips and eyes and breathing difficulties.

Food allergies can be fatal.

An acute allergic reaction, or anaphylaxis, can occur within seconds or minutes of exposure to the offending food. If not treated immediately, it may lead to unconsciousness and even death.

Common food allergens include eggs, peanuts and seafood like prawns, said Dr Law.

Food intolerance, though more common, is rarely life-threatening.

People with food intolerances can eat small amounts of the offending food without distress.

However, for those with food allergies, eating even a tiny amount of the food may trigger rapid and severe reactions, Dr Law said.

Lactose intolerance

Among Asians, the most common food intolerance is lactose intolerance. Thiscondition occurs because the body does not have enough lactase enzymes needed to digest lactose, a sugar found in milk.

The undigested lactose passes through the digestive system, causing nausea, abdominal cramps, bloating, gas and diarrhoea.

Compared to other races, Asians are more genetically predisposed to lactase deficiency, said Associate Professor Gwee Kok Ann, a consultant gastroenterologist at the Stomach, Liver and Bowel Clinic. “It is not abnormal though, as there are more people with lactase deficiency than those without,” he said.

He said lactase deficiency does not predispose a person to any disease. In fact, he said there is a hypothesis that the lactase deficiency gene may confer a survival advantage in certain diseases such as malaria.

About 90 per cent of Singaporeans are lactose intolerant to varying degrees, he said.

Professor Phua Kong Boo, the head and senior consultant of gastroenterology service at KK Women’s and Children’s Hospital, explained that some people cannot tolerate any form of milk or milk products like cheese and ice cream, while others can take small amounts of milk added to tea without any adverse reaction.

Apart from genetic causes, lactose intolerance can sometimes occur when an injury to the small intestine causes it to produce less lactase. It typically lasts from days to a few weeks and is reversible, said Prof Phua.

In rare cases, babies are born lactose intolerant because of a congenital defect.

Symptoms of lactose intolerance typically disappear when foods high in dietary lactose are removed from the diet.

People with lactose intolerance may want to experiment with consuming varying amounts of milk and its products to determine their threshold, said Prof Phua.

Gluten intolerance

Gluten intolerance is a condition that occurs when the body cannot tolerate gluten, a protein found in wheat, barley and rye. Common foods containing gluten include bread, wheat pasta and biscuits.

This condition is typically seen in people with coeliac disease, a digestive condition.

When someone with the disease eats food containing gluten, his immune system responds by damaging or destroying villi – the tiny, finger-like protrusions lining the small intestine.

The damage usually results in an insufficient production of digestive enzymes that break down food.

Left unabsorbed, large components of food remain in the digestive tract. They then ferment, causing cramps, gas, bloating, flatulence and diarrhoea, said Associate Professor Lynette Shek, a senior consultant at the University Children's Medical Institute at National University Hospital.

Absorption of certain nutrients like proteins, carbohydrates and lactose is often compromised too.

While coeliac disease involves an immune system response, it is considered a more complex food reaction than a food allergy.

It can occur at any age, but is more prevalent in adults.

Coeliac disease is more common in Caucasians: about one in 100 people in Britain is affected. It is thought to rarely affect people here. This may, however, change.

No local statistics are available, but Prof Gwee estimates that more Singaporeans will be afflicted with the condition, partly due to an increased consumption of wheat-based products.

The disease’s exact cause is unknown but it is often inherited, he said. It can also develop after an infection, say an episode of food poisoning.

Coeliac disease has no cure, but can be effectively managed by following a gluten-free diet.

“Symptoms usually go away once patients remove gluten from their diet,” said Prof Gwee.