What's in our food: Drink up, it's good and bad for you

* In this third part of a week-long series on food, Herald science and health reporters research the truth about the food groups we rely on.

From fruit, vegetables and meat, to today's special focus on dairy products, a look at grains and cereals tomorrow and followed by takeaways, we ask what is good for you these days.

Don't say it too loudly, but most people cannot tolerate New Zealand's biggest export, cow's milk.

Outside the European race, most do not have enough of a substance called lactase, needed to break down milk's major sugar, lactose, so the body can draw energy from it.

So if they do drink cow's milk, they get bloating, stomach pains and diarrhoea.

Some natural therapists believe longer-term consequences include colds, asthma, glue ear and even cancer.

Full milk, butter, margarine and cheese are also - with meat - the biggest sources in the New Zealand diet of hard "saturated fats" which are a major cause of our high death rate from heart disease.

In Staying Healthy with Nutrition, Dr Elson Haas says flatly: "In general, I do not recommend the drinking of milk for adults."

But milk and milk products also give us more than half the calcium we need to maintain the strength of bones and teeth and helps with transmitting nerve impulses and with blood clotting.

So can milk be good and bad for us?

Nutritional guidelines in North America, northern Europe and Australasia treat dairy products as one of the four food groups in a healthy diet.

New Zealand guidelines published by the Ministry of Health last year, recommend at least two servings of low-fat milk and dairy products a day, with at least five servings of fruit and vegetables, six servings of wholegrain bread and cereals and one serving of meat, fish, eggs, nuts or beans.

A "serving" is a large glass of milk (250ml), a 150g pottle of yoghurt, two slices of cheese (40g) or two scoops of ice cream (140g).

As well as providing just over half our calcium, dairy products provide a sixth of our intake of protein, which builds muscles and bones.

Dairy products also give us 29 per cent of our fat, which supplies and stores energy.

Nutritionists are worried that our consumption of milk has dropped by a third, from 139 litres a head in 1974 to about 90 litres today.

The 1997 national nutrition survey found that 15 per cent of men and 25 per cent of women, including 37 per cent of teenage girls, were getting less calcium than they needed to grow strong bones.

A study of 250 Dunedin children two years ago found that children who did not drink milk were on average 0.7cm shorter than normal and had 3 1/2 times the normal rate of broken bones.

They were also twice as likely as other children to be overweight, possibly because they drank sugary soft drinks and fruit juice instead of milk.

If you miss out on calcium as a child, you can never make it up. Our bone weight peaks at the age of 18 to 20, generally holds until menopause in women and the late fifties in men, and then drops by a quarter or more in old age.

This means teenagers who miss out on calcium today are more likely to suffer broken bones and osteoporosis when they reach old age around the middle of this century.

This does not necessarily mean that they should drink more milk. Despite the recent decline, New Zealanders drink about the same amount of milk as Americans and Russians, a quarter more than the average European and 15 times as much as the average Chinese.

Tofu has only about 10 per cent less calcium than standard milk, and other soy products, nuts, seeds, canned fish and leafy green vegetables such as parsley and spring onions all have high calcium levels.

Even calcium intakes themselves vary widely, without apparent ill effects.

Finns get almost twice as much calcium as New Zealanders, and Japanese get less than half as much - yet elderly Finnish women die in falls at six times the rate of their Japanese contemporaries.

Ironically, Japanese bones may be stronger partly because they drink less milk and eat less meat.

A 1997 Food and Agriculture Organisation report cited several studies showing that people who eat more animal protein also excrete more calcium in their urine, so they need to take in more calcium than people in more vegetarian countries.

We all need some fat in our diet to give us energy, to store energy for lean times, to insulate our bodies and to protect our internal organs.

But the 35 per cent of energy we get from fat in New Zealand is far higher than in Africa and Asia, where it is often as low as 10 per cent.

Moreover, we get 15 per cent of our total energy from saturated fat, more than even America and Australia.

This is the "bad fat" blamed for deaths from heart disease.

By far the biggest source of it in our diet is dairy products.

A Mars bar is 11 per cent saturated fat. Standard milk is only 2 per cent saturated fat, but cheddar cheese is 22 per cent and butter 53 to 55 per cent - "yellow poison", says dietitian Christine Cook.

Although New Zealanders have been turning away from butter, we still eat more of it than people in any other country.

The Ministry of Health estimated last year that high cholesterol linked to saturated fats killed almost 5000 New Zealanders through heart attacks each year.

It recommended a campaign to halve our butter consumption - and even then we would still be using more than Australians.

A Consumers Institute survey found plenty of monounsaturated and polyunsaturated spreads on the market with much lower levels of saturated fats than butter.

Margarine is a high-fat product too. By law, anything calling itself "margarine" or "butter" must be at least 80 per cent fat. But margarine's fat is mostly unsaturated and less damaging to the arteries.

The lowest-fat spread on the list, Flora Pro-activ Light, has only 38 per cent fat and contains plant sterols, a kind of plant version of fats, which are poorly absorbed by the body and interfere with the absorption of their animal equivalent, cholesterol.

All newborn mammals start life drinking their mothers' milk.

They are born with enough lactase to break down the lactose in the milk so it can be absorbed by the baby's growing body.

In all other mammals, and in almost all human races, the youngster stops producing lactase by the age of 2 or 3, soon after it stops breastfeeding - a clear sign that we were not made originally to keep drinking milk past infancy.

But most northern European people, about half the people of southern Europe and a few pastoral tribes

in Africa have evolved a genetic variant, allowing them to keep producing lactase - and therefore drinking milk - throughout their lives.

In New Zealand, 91 per cent of Pakeha - but only 46 per cent of Samoans, 36 per cent of Maori, 35 per cent of Indians and 20 per cent of Chinese - keep producing lactase into adulthood.

Everyone else is "lactose intolerant", and can drink only small amounts of milk without side-effects.

Cows are milked in countries where most people are lactose-intolerant. But the milk is usually fermented to break down the lactose and is eaten as cheeses, curds and yoghurts.

Scientists believe the northern European genetic variant evolved when humans migrated from the tropics, where calcium was abundant from plant sources, into colder regions, where calcium was much harder to find.

Natural therapist Walter Last, in his book Healing Foods (1992), recommended that even lactose-tolerant people should keep milk to a minimum because it often produced a buildup of mucus, sometimes worsening diseases such as asthma, cystic fibrosis and cancer.

But an American study the next year gave people a glass of cow's milk and a glass of soy milk and found that people reported the same mucus problems with both and could not tell the difference between them.

A popular recent theory is that we could avoid heart disease and diabetes by adopting the "Palaeolithic" diet of our pre-agricultural ancestors, who ate a low-fat, high-carbohydrate menu of fruits, nuts, leafy vegetables, meat, fish and insects - but not dairy products or cereals.

National Heart Foundation dietitian David Roberts thinks that would be going too far.

In effect, Europeans have evolved to tolerate milk.

He says: "There is a role for low-fat milk and milk products in a healthy dietary pattern."