Dietary complaints - as well as food preferences - tend to run in families and in racial groups.
Lactose intolerance, the inability to digest the natural sugar of milk lactose, is a trait shared by most of the world's adult population.
Around 90 per cent of Asian people, Australian Aborigines, Maori and islanders, Middle Eastern and Africans share this metabolism.
After childhood, they are unable to break down the lactose they eat. If they drink it in large enough quantity, it can cause bloating, tummy pain, flatulence and even diarrhoea.
Their traditional diets reflect this. Any dairy products they consume are ``cultured'' (such as yoghurt, buttermilks and soft cheeses) as the live bacteria convert much of the lactose into a safer lactic acid.
Lactose intolerance is much less common in anyone of northern European descent, whose ancestors herded dairy cows for years, continued to drink milk and consequently retain the enzyme needed to split the lactose molecule.
Geneticists now believe the gene for lactose intolerance has been around for a long time and was in fact the "original" form of the gene. In other words, all humans were once lactose intolerant.
If you fit this racial inheritance, it seems wise not to drink large quantities of milk on a regular basis, but to enjoy cheeses and yoghurt for your calcium. Note that small amounts of lactose (say milk in tea or coffee or on cereal) can usually be fine. And the more you are exposed to lactose, the more your digestive system is be able to cope with it, as successive generations of Asian kids adapt to a more Western diet and drink milk.
Catherine Saxelby is a nutritionist and author of Nutrition for Life. Get more healthy eating tips at www.foodwatch.com.au