What's in our food: You are what you eat - tracking your diet

"Is it safe to eat?"

That's the question Canterbury University's Professor Ian Shaw asks in a forthcoming book, which is being made into a TV1 series by Auckland's Top Shelf Productions.

We all know the story. Despite all the warnings, many people can't resist fatty and sugary foods and don't exercise enough.

The cup of coffee that wakes us up in the mornings has been linked to bladder cancer.

Most breakfast cereals are so sugary they may give children attention deficit disorder in the short term and diabetes eventually.

Pesticide residue is found on 94 per cent of all the bread we eat and 69 per cent of apples, says the Safe Food Campaign.

Beef risks mad cow disease, chicken is liable to be chock-full with antibiotics if not campylobacter, and fish might contain mercury or worse.

NZ King Salmon acknowledged this year that it uses small amounts of formalin in a bath treatment for its salmon, a parasite treatment which is banned in Europe.

Salad vegetables such as lettuce and cucumber also figure in the Safe Food Campaign's "dirty dozen" of most spray-drenched foods.

Dietitians Christine Cook, Pip Duncan and Kate Sladden all steer clear of butter - "yellow poison" which has a higher proportion of saturated fat (55 per cent) than any other food in the food tables, and is possibly contributing to New Zealand's high rate of heart disease.

But the convener of the National Consumers' Food Safety Network, Dr Meriel Watts, says butter is "more natural" than the alternative of margarine and has fewer trans-fats and additives.

Yet somehow we have to steer our way through this minefield, because we all have to eat.

In fact our bodies are robust enough to draw energy from almost any other animal or plant, and even to absorb minerals directly from water, soil and the air around us.

We need a surprisingly small number of things in any bulk. Just four elements - hydrogen, oxygen, carbon and nitrogen - make up 96.3 per cent of our bodies.

These are organised in the form of water (hydrogen and oxygen), carbohydrates, fats and oils (all made of hydrogen, oxygen and carbon), and proteins (hydrogen, oxygen, carbon and nitrogen).

We also need small amounts of many other things, such as calcium for our bones, phosphorous to help build the nucleic acids that carry our genetic instructions, and "vitamins" - a group of compounds that are essential to various bodily functions.

Nutritionists say we can get these essentials from a balanced diet of four food groups:

* Fruit and vegetables: at least five servings a day, where a serving is one piece of fruit or vegetable or half a cup of salad or fruit salad.

* Milk products: two servings a day, where a serving is a glass of milk, a pot of yoghurt or two slices of cheese.

* Bread and cereals: six servings a day, where a serving is a slice of bread or a cup of cornflakes, rice or pasta.

* Meat, eggs and beans: one serving a day, where a serving is two slices of meat, one steak, one chicken leg, one fish fillet, one egg or three-quarters of a cup of beans.

During the next five days, the Herald will examine these four food groups - and takeaways, which many of us now depend on to cover all four.

We need to eat from all four groups. But what, in each group, is still safe to eat?