What is lactose intolerance?

Lactose intolerance refers to difficulty in digesting milk and milk products, causing symptoms such as abdominal discomfort, a bloated feeling, wind and watery diarrhoea. Lactose-intolerant people can often cope with small servings of lactose foods, but otherwise should aim for lactose free and low lactose products.

About lactose

Lactose is a complex carbohydrate (sugar) that is present in milk. During digestion, lactose is broken down into two simpler sugars, glucose and galactose. An enzyme called lactase that is made in the small bowel is necessary for this process. Some people do not have enough lactase (lactase deficiency) and have difficulty digesting milk and milk products - lactose intolerance.

Symptoms of lactose intolerance

The main symptoms of lactose intolerance are abdominal discomfort or pain, a bloated feeling, wind and watery diarrhoea. The symptoms usually develop 30 minutes to two hours after eating or drinking products containing lactose.

Lactose intolerance is different from a milk allergy. A genuine allergic reaction usually causes symptoms such as an itchy skin rash, swelling of the lips or difficulty breathing.

Tests for lactose intolerance

A lactose challenge test can help determine whether lactose intolerance is likely. This test involves drinking half a glass of milk and seeing if symptoms develop. If lactose intolerance is suspected, you doctor may suggest you avoid foods that contain lactose for a few weeks to see if your symptoms improve. If the symptoms return when you re-introduce lactose to your diet, you most likely have lactose intolerance.

Special tests, including a formal lactose tolerance test and measuring the lactase concentration in the small bowel are available.

Modify diet

Dietary modification is the main treatment for lactose intolerance. Most lactose-intolerant people do not have to avoid lactose entirely, they just need to be sensible and not overdo it.

Choose products that are low in lactose or lactose-free when possible. Milk and milk products should generally still be included in the diet because they are valuable sources of calcium, but do not eat or drink large quantities of lactose-containing products at one time - spread it out over the course of the day. Eating dairy products along with a meal can also help.  Small amounts of lactose (eg 10g a day) can usually be tolerated.

High-lactose foods

Foods with a high lactose content (more than 4g per serve) include:

• milk
• custard
• dairy desserts
• yoghurt (although yoghurt is often tolerated because the lactose is partially digested by bacterial cultures in the yoghurt).

There is a moderate amount of lactose (0.1 to 4g per serve) in ice cream, cream and soft cheeses (such as cream cheese, cottage cheese and ricotta cheese). Hard cheeses such as cheddar cheese have only very small amounts of lactose (less than 0.1g per serve) and generally cause no symptoms.

Lactose in medicines

Lactose is an ingredient in some medicines, including certain brands of the oral contraceptive pill. Usually, lactose in medicines only causes symptoms in people with severe lactose intolerance. It is generally not necessary to avoid taking medicines that contain small amounts of lactose. But you might want to check your medicines to find out if they contain lactose because there may be lactose-free alternatives available.

Lactase enzyme

Lactase enzyme is available over-the-counter in pharmacies, and can be used by people who still experience symptoms despite dietary changes. It can be taken as drops or tablets before drinking milk or eating dairy products.

Secondary lactase deficiency

Lactase deficiency can occur on a temporary basis after a bout of gastroenteritis, or in people with coeliac disease or Crohn’s disease (a type of inflammatory bowel disease).

Finding milk and lactose-free products

The New Zealand Manufactured Food Database produces commercial food lists (lists of "safe food") of New Zealand brand name foods, including milk and lactose-free products. The NZ MFD can be visited on www.mfd.co.nz.

Original material provided by myDr, July 2011. Edited by everybody, February 2012.