If you are among those who have trouble digesting milk or milk products, you may be suffering from lactose intolerance. Dr Wynnie Chan explains what it is and what your alternatives are

Have you ever felt bloated after having a glass of milk or got crampy after eating a pot of yoghurt? If so, you may be suffering from lactose intolerance, an affliction that occurs when the body is unable to digest lactose, a sugar found in milk. In order for lactose to be absorbed, it must be broken down by an enzyme called lactase, which is produced in the lining of the stomach. Lactase is usually secreted along with the other digestive enzymes, but people who suffer from lactose intolerance don't produce lactase in sufficient quantities for the milk sugar to be broken down. The result is that lactose passes through the body undigested, causing stomach pain, bloating and diarrhoea.

An inability to digest lactose is usually hereditary. It tends to be more common in adolescents and adults from South East Asia, India, the Middle East and parts of Africa where milk is normally not consumed after infancy and therefore the natural production of the enzyme lactase decreases at a young age. Many people (particularly infants whose systems are prone to infections) experience temporary lactose intolerance if they have suffered from a gastrointestinal infection. This lasts only a few days and occurs because such infections can damage the stomach lining causing a sensitivity, or intolerance, to lactose.

Because milk and milk products form a large food group that provide an important source of calcium, protein, vitamins B12, and vitamins A and D, omitting these foods from your diet without appropriate substitutions can pose a serious risk of malnutrition. Women and children who eliminate milk and milk products from their diets are at the greatest risk. Children need adequate amounts of calcium to grow and build strong, healthy bones and teeth, while women need calcium throughout their lives to prevent the development of osteoporosis.

Fortunately for most people with lactose intolerance, small quantities of ordinary milk and dairy products such as yoghurt, hard cheeses and lactose-reduced milk can usually be consumed without significant symptoms. This is because hard cheeses and lactose-reduced milk have lower levels of lactose and the bacteria present in yoghurt is believed to actually produce lactase, which leads to partial digestion of lactose in the gut.

If you suspect that you or your child is intolerant to a particular food, it's important to seek professional advice before eliminating this food from his or her diet. If either you or your child are about to start a lactose-free diet, bear in mind the following points:

• Human milk, cow's milk, sheep and goat's milk, yoghurt, cream and cheese contain lactose. Yoghurts, reduced-lactose milk and hard cheeses are usually easier to digest.

• Butter and most margarines contain lactose. Tomor (a type of margarine), lard, vegetable oils and some low-fat spreads are lactose-free.

• Cakes, biscuits, bread and pastry containing milk, milk puddings and ice cream all contain lactose.

• Lactose is contained in many medicinal preparations (both over the counter and on prescription).

• Soya products, such as calcium fortified soya milk and tofu, are good calcium substitutes.

• Some breakfast cereals contain milk. Be sure to check the label for the presence of lactose or skimmed milk powder.

• Some breads - e.g. milk loaf or toasting loaf - contain milk, while standard white, brown and wholemeal breads do not.

Soya milk:
Soymilk, or soyamilk, looks like cow's milk but is actually the milk extract from soya beans. Although the taste is different to cow's milk, it is not unpleasant. For a tastier option, try the vanilla or chocolate flavoured versions, or the naturally sweetened variant. If used in place of cow's milk, calcium-fortified soymilks are recommended. A wide range of brands can be found in all health food shops while supermarkets such as Tesco make their own brand.

Soya yoghurt:
Soya yoghurt is made from soya milk and has the same consistency as dairy yoghurt, although the taste may take some getting used to. Provamel comes in a variety of flavours and is a well-known brand. Although some supermarkets do sell it, you may have go to a health food shop to find it.

Tofu:
Tofu is made by separating soymilk into curds and whey, in the same way that cheese is made by separating animal's milk. Tofu comes in two consistencies - soft and firm - and can be used in place of meat in stir-fries or stews. It can be found in most supermarkets, although for a wider variety - including barbecue and curry flavoured tofu - visit your local health food shop.

Soya cheese:
Soya cheese is made from tofu and has a similar consistency to animal cheese, although it can be slightly rubbery. The taste may also take some getting used to but it does function well as a cheese substitute in dishes like lasagna or on pizza. Galaxy - one of the more popular brands - makes rice and veggie slices which come in mozzarella and cheddar flavours; Redwood and Soyco make rice and vegetarian parmesan cheeses.

Non-dairy ice cream:
There is a wide range of non-dairy ice cream alternatives which are quite tasty and come in a range of traditional ice cream flavours like chocolate and vanilla. Of all the tofu products available, this is the one that tastes most like the real thing. Winner's Swedish Glace is a popular brand and is available in some health food shops. Another good alternative to dairy ice cream is sorbet, which can be found in most supermarkets.

Other:
Tropicana make an orange juice which is calcium fortified and Danone manufacture calcium fortified 'Activ Water', both of which are good dairy-free sources of calcium and are available at most supermarkets.

If you need inspiration on how to convert to a dairy-free diet, take a cue from our one-day menu:

Breakfast
1 small bowl of Cornflakes, topped with a large serving (or large handful) of strawberries served with 125ml calcium-fortified soya milk
2 pieces of wholemeal toast served with two tsp strawberry jam and 2 tsp weight watcher's low-fat spread

Lunch
1 medium bowl of vegetable soup
1 large wholemeal pitta bread stuffed with humous and grated carrots
1 pot soya yoghurt

Dinner
1 grilled chicken breast. Marinate it with 1 clove garlic, crushed, 1 tbsp
teriyaki sauce and 1 tsp sesame oil for 10 minutes. Then, grill for 10 minutes under a moderate heat.
1 large bowl of young spinach leaves and swiss chard salad. Dress with 1 tbsp tofu dressing, available from your local health food shop.
1 large baked sweet potato
1 bowl of fruit salad topped with 1 pot soya yoghurt

Snacks
1 glass fruit juice
2 pieces of fruit
1 glass of calcium-fortified soya milk