What's in our food: Hazard that's hard to swallow

Everyone agrees that fresh fruit and vegetables are good for us.

"It's not possible to eat too much fruit and vegetables," Auckland Regional Public Health Service dietitian Christine Cook says.

Despite concerns about pesticide residues, Dr Meriel Watts of the Food Safety Network agrees.

"I never say to anyone don't eat any fruit and vegetables because it's got residues," she says. "Our residues are not so bad that you should stop eating them."

In fact, our residues are bad by international standards. Australian and New Zealand foods have much higher residues than American food from both fungicides, sprayed mainly on fruit and vegetables, and organophosphorous pesticides, sprayed mainly on grains.

On the other hand, in absolute terms, all pesticide residues are tiny. All contaminants in the most heavily polluted crop of the six examples in our table, lettuce, add up to about one six-millionth of a lettuce.

At the other extreme, contaminants amount to only one 160-millionth of a kiwifruit, and cannot be detected in oranges at all.

So should we be worried? We need to consider both sides of the ledger.

NUTRIENTS

On average, New Zealand men eat more than they need for the amount of physical activity they do. They eat twice as much protein, about a third more sugar and a fifth more fat, than they need.

Women eat about two-thirds more protein, a third more sugar and slightly more fat than they need.

The only kind of food that men eat about the right amount of, and that women don't eat enough of, is non-sugar carbohydrates.

Dietitians therefore recommend that we should all eat more foods that are high in non-sugar carbohydrates and low in protein, sugar and fat.

Bread and cereals have the most non-sugar carbohydrates and are generally low-fat and with moderate protein. Fewer than one in five of us eats the recommended six servings a day of breads and cereals.

But dietitians are cautious about advising us to eat more bread and cereals, because we tend to eat them with lashings of things that are bad for us such as butter and sugar.

So all the emphasis is on the other kind of "good" food: fruit and vegetables. Although fruits have lots of natural sugars, they have virtually no fat and very little protein, so filling up on them means we are less likely to eat fatty, protein-rich foods.

Fruit and vegetables are also our major source of vitamin C and other trace nutrients that are vital for various bodily functions.

"We encourage people to eat a wide variety of fruit and vegetables to get everything," says dietitian Pip Duncan.

It's not just your greens that count - the experts recommend at least three colours of vegetables a day.

"Have a rainbow every day," says Christine Cook.

Her colleague, Kate Sladden, says canned and frozen produce is just as good as the fresh stuff, which may actually have taken a day or two to get to your shopping trolley.

Humans are natural omnivores. We have evolved carnivorous features such as eyes at the front to catch prey with binocular vision, but our ancestors were vegetarian apes and our bodies are still made to survive mainly on plants.

"It is just in the last century that the meat foods have been so heavily consumed in the Westernised cultures," writes American nutritionist Elson Haas in Staying Healthy with Nutrition.

More meat and other fatty foods have brought epidemics of heart disease, cancer and diabetes, although better health care and perhaps better eating have begun to lower the first two of those in the past 20 years.

"In the long run," writes Dr Haas, "a diet centred around whole grains and vegetables would best serve us individually as well as contribute to greater planetary harmony."

CONTAMINANTS

Pesticides are toxic. They are sprayed on plants to kill weeds, bugs and fungus.

They carry warning labels such as "Harmful if swallowed, inhaled or absorbed through skin".

In very small amounts, they are everywhere - found in at least one sample of 91 out of 121 foods in the Food Safety Authority's 2003-04 total diet survey so far.

Among fresh fruit and vegetables, only oranges are totally "clean".

Full results of the latest survey are still being analysed, but in the last one in 1997-98, pesticide residues showed up in 59 per cent of all food samples. The chances are that they are in most things we eat.

In all but one case, the residues averaged less than 3 per cent of the "acceptable daily intake" for the most vulnerable group, toddlers. But for one group of fungicides, dithiocarbamates, the average toddler consumed 23 per cent of the acceptable intake, suggesting that some toddlers may have taken in more than the limit.

In any case, Alison White of the Pesticide Action Network says the acceptable limits are "little more than a calculated guess".

They are based on the levels at which pesticides affected health in animal experiments, adjusted upwards for the relative body weight of humans, and then down again, usually to 1 per cent of that figure, for extra safety.

They ignore the "cocktail effect" of taking in many pesticides over a lifetime, and the fact that even the tiniest amounts of some chemicals may be enough to "programme" a developing foetus in a pregnant woman.

A World Health Organisation report in 2002 noted that vinclozolin, a fungicide found in New Zealand kiwifruit in the latest survey, blocks male sex hormones from binding to the male sex hormone receptor in mammals and may cause deformed male offspring.

Experiments on pregnant rats showed that even the lowest dose of 3mg of vinclozolin a day for every kilogram of the rat's body weight produced male baby rats with nipples and short penises.

It is extremely unlikely that eating kiwifruit would produce the same effects in humans. A pregnant woman would have to eat about 400,000 medium-sized kiwifruit a day to get the equivalent dose of 3mg of vinclozolin a day for every kilogram of her body weight.

But no one has ever actually done the experiment with lower doses, or observed the results generations later, or checked whether there is a particular time in the growth of an unborn baby when even a few specks of vinclozolin just might screw things up.

"The risks are largely unknown," says Dr Watts. "We don't have sufficient science to say the residues are safe."

Most experts are still prepared to risk eating sprayed fruit and vegetables - after washing them first.

Dr Diane Bourn, an Otago food scientist who did what a Canadian paper described as "by far the most thorough review of the literature" comparing sprayed and organic food, says there is no evidence that microscopic pesticide residues do anyone any harm.

"We don't know for sure whether residues below the maximum residue levels are okay healthwise or not," she says.

"But we know they are toxic to farm workers. They are toxic to the environment. Whether they are toxic for our health is debateable, and surely the better way is to look at ways of reducing them."