Patricia Thompson - NUTRITION TALKMANY PEOPLE accept the premise that if a little is good, then more is better. This is not always the case with nutrition, as too much can actually be harmful. Hippocrates said, 'Let food be your medicine and let medicine be your food'. This recognises that food carries medicinal properties and, as with all medicines, you can overdose, resulting in negative symptoms. While most persons accept that excessive intake of fat, meat and other foods from animals can have negative effects, it is the general feeling that we should eat plenty of foods of plant origin.
PLANT TOXINS
Plant foods are especially useful because unlike foods from animals, they can be eaten raw and unprocessed. This means that the enzymes, phytochemicals and nutrients are obtained in a pure form and have potent effects in boosting the immune system and performing other regulatory functions that keep chronic disease conditions in check. Some plant foods, however, have toxic substances and when these accumulate in the body, they can be harmful.
Raw cabbage and other cruciferous vegetables, for example, are protective against cancer because of the glucosinolates, but excess of some of these same substances called goitrogens can affect how the body uses iodine resulting in goitrous effects. Average intakes of glucosinolates from vegetables in Great Britain was found to be 76mg/day and clinical effects were found to appear at intakes of 100-400mg/day.
The dark-green leafy vegetables are rich in calcium and iron but they also contain high levels of the inhibitor, oxalate. At normal eating levels, this is not a problem and we can also benefit from the phytoestrogens, but excessive intakes of spinach or beetroot can lead to oxalate complexes aggravating kidney stones in those who are prone to this. Another example is soybean and other legumes which contain an inhibitor against the amino acid of protein called trypsin. Fortunately, these are destroyed by cooking.
NUTRIENTS AS DRUGS
In the same vein, many nutrients have more than nutritional effects when taken in larger quantities than the recommended dietary allowance (RDA). For example, the B vitamin niacin at a level of 3000mg daily has been used to treat high cholesterol levels and has been shown to reduce the incidence of heart disease. The RDA is only 15-20mg daily. At such medicinal levels, however, it may cause flushing of the skin, headache, nausea, heartburn and diarrhoea. It is also capable of damaging the liver, activating peptic ulcers, impairing glucose tolerance and enhancing the build-up of uric acid leading to gout attack.
Vitamin C is a useful antioxidant vitamin that helps reduce the risk of a number of conditions, including heart disease and some cancers. It has been popularised for reducing the symptoms of an oncoming cold or flu. However, at pharmacologic doses greater than 2000mg daily, there may be negative effects such as stomach cramps, nausea and diarrhoea. Taken routinely for months or years, it can lead to the formation of kidney stones, reduced anti-bacterial ability of the body and removal of the calcium from bones.
The above are just a few examples where abuse is common, but fortunately, tolerance levels vary from person to person. The philosopher Paracelsus, said 'Poison is in everything and nothing is without poison; it is the dosage that makes it either poison or remedy'. It is therefore best to use a mixture of foods in moderate quantities to supply us with the needed nutritional benefits for optimum health rather than restricting our intake to too much of a few nutritious foods.
Patricia Thompson M.Sc., Registered Nutritionist, Nutrition and Diet Services; email: yourhealth@gleanerjm.com.
