Dr Geoffrey Savage
21 January 2005
Now and then you hear people say that there are chemicals in our food and that the amounts are increasing. For these people the news is not good: it turns out that food is made up entirely of chemicals, and without chemicals there would be no food.
It is possible that when people refer to chemicals they are trying to make the distinction between good chemicals we need every day to keep our bodies healthy - proteins, fats, carbohydrates (sugars and fibre), minerals and vitamins - and other chemicals we could perhaps do without. It is also possible that chemicals in our food means a number of compounds that are added to processed foods as preservatives. In a curious way consumers have demanded that these compounds are included. People get very annoyed when food goes off quickly and has to be thrown away. If various preservatives were not added, many foods would spoil rapidly. The typical Kiwi family camping holiday would be almost impossible.
Are chemical food additives dangerous to human health? Generally no. It is much more dangerous to eat mouldy food or food that may contain microbial toxins or food that is rancid. Nowadays food manufacturers are very concerned about their image and they only add preservatives where necessary. And they certainly do not add excess amounts. This is partly to meet the current food regulations and partly to control costs. Why add an unnecessarily high level of preservatives that cost money and do not add to the value of the product? Food manufacturers are extremely image conscious and are determined to be around for a long time.
An example of a common additive is salt. Salt is essential for life but if it is consumed in larger amounts it can predispose to the development of hypertension. Consumed in much larger amounts it can kill. When added to foods in the correct amounts it is a very effective preservative and of course it adds flavour.
It might be a surprise for people to learn that toxic chemicals are abundant in nature, and that includes the vegetable garden. Every gardener knows that there is a permanent state of war going on in their vege patch between the things we want to eat and insects that want to devour them first. The plants respond to these attacks by manufacturing toxic compounds that will kill the insects. There are many different plants that do this, including legume plants such as beans, lentils, mung beans and chickpeas. These plants make compounds that bind to an insect's digestive enzymes. If, for example, a caterpillar continues to eat the legume its digestive system is disabled and it will die. The same thing will happen to humans too. These toxic compounds will bind to our own digestive enzymes and if we continue to eat raw legume seeds in large amounts it is possible to become very sick and even die. In many Asian countries these foods make up a big part of the normal diet, and humans suffer no ill effect. There are three main reasons for this. First, many compounds have to be eaten in large amounts to have an adverse effect and, second, the body has effective enzyme systems for processing chemicals the body doesn t want or need. Most of these enzyme systems reside in the liver. A properly functioning liver makes no distinction between natural and synthetic (man-made) compounds. It simply gets on with the job of breaking them down into simpler units so that they can be excreted. With the exception of some persistent compounds, such as the organochlorines, most are readily processed through various types of bio-transformation.
The third reason is that humans have the advantage of being able to cook their food. Cooking beans, lentils and chickpeas not only makes them much more palatable and tasty to eat, it also breaks down the inhibitors in the food. These inhibitors are quite resistant to boiling, and so these foods have to be cooked for a relatively long time, but it explains why there are millions of healthy Asians consuming a diet high in natural insecticides.
The number of insecticides that can be safely used on food plants has been reduced considerably in recent years and the use of the permitted ones is very carefully controlled. The levels that are commonly found in New Zealand foods have been shown to have no adverse effects even when fed to animals at much, much higher levels. We have a peculiar relationship with the use of insecticides on food plants. We like our foods to be clean and unblemished and we would be incensed if we found bugs in a commercially grown lettuce. That being the case we have to tolerate low levels of insecticides in our food. The only alternative is only consume food produced organically, which generally uses cultivars with higher levels of natural protection, ie, more of their own toxins.
The level of added chemicals in food we produce in New Zealand is well within accepted international standards. We are fortunate to have a Food Safety Authority that monitors our food closely. We are educated and economically secure enough to make informed choices about the quality of the food we eat. As far as our overall health is concerned, the amount of chemicals in our food should be the least of our worries.
Dr Geoffrey Savage is Senior Lecturer in Food Biochemistry at Lincoln University .