LOGICAL ERRORS

Errors in logic are sometimes the basis of myths about food and nutrition.
For example:


1. A simple association is mistaken for a cause-and-effect relationship.

"I was eating cucumber when I developed central chest pain which turned out to be a heart attack."

Analysis: It may have been pure chance that the heart attack occurred during consumption of the food in question. Many factors, including food intake, over an extended period of time contribute to heart attack. There may have been precipitating factors other than food consumption operating at the time of the heart attack, although these may not have been obvious to the person suffering the attack.


2. The primary cause of a disease is mistaken for the only factor involved in becoming ill.

'Measles is caused by a virus, so the way children eat is not going to help them avoid measles'.

Analysis: In fact, protein-energy malnutrition is one of the factors which most predisposes people, especially children, towards fatal measles infections. This is because a person's nutritional status determines, in part, their resistance to infection. 'Nutrition status' is the biological consequence of the way in which we eat (or, if we cannot eat, take in food through a vein or tube); it is reflected in how much muscle and fat we have, what our blood protein levels are, how well our body's defence system works, whether we can make blood cells and much more. Genetic and other factors are also involved in resistance to disease. Whether someone catches a particular disease almost always depends on the interaction of several factors, only one of which is their exposure to a particular disease-causing agent such as a virus. This partly explains why a particular agent or food or way of eating does not necessarily carry the same risk for all individuals.


3. The amount of nutrient in a food is mistakenly thought to be the main factor determining the value of that food.

'Wholegrain cereals do not contain as much iron as meat, therefore vegetarians are at risk of iron deficiency.

Analysis: The availability to the body of a particular nutrient (iron in this case) is affected by more than just the amount of that nutrient in the food or even the whole meal. For example, phytate found with dietary fibre, phytase (an enzyme from yeast), or tannin from tea affects the bioavailability of iron from our diet (the extent to which the iron in food can be used by the body). The food components that have no nutritive value must also be considered because they may react chemically with some of the nutrients, or have physiological effects. For example, phyto-oestrogens in some plants (substances with female sex hormone-like properties) could modify the menstrual cycle and menstrual blood and iron loss in some women who eat these plants in sufficient quantity. It must be re: umbered that foods are chemically complex mixture and not simply sources of particular combinations nutrients.