Using the thinking map for skilful causal explanation (see the start of this section) to guide you, briefl y evaluate the following reasoning: Studies on individuals have attempted to determine...

Using the thinking map for skilful causal explanation (see the start of this section) to guide you, briefl y evaluate the following reasoning: Studies on individuals have attempted to determine whether raising the consumption of cholesterol affects the level of blood cholesterol. For example, volunteers drank four pints of milk a day for a period: their blood cholesterol levels were unaffected. Even more damaging to the hypothesis that ingested cholesterol can damage the heart are the results of two recent and independent studies funded by the British Medical Research Council. One found that men who drink no milk have ten times as many heart attacks as men who drink more than a pint a day. The other discovered that men who eat margarine have twice as many heart attacks as those who eat butter. There are in fact good reasons why one would not expect blood cholesterol to vary with diet. First, the liver manufactures three or four times as much cholesterol as is normally ingested. Secondly, the body itself regulates the amount of cholesterol in the blood: its level is normally kept constant regardless of what is eaten, though some unfortunate people have too high a setting and are likely to die young through heart attacks. The true causes of high blood cholesterol are not known. What is known is that although reducing blood cholesterol levels by drugs reduces heart disease, it does not increase longevity: people die of cancer instead. There is no solid evidence that cholesterol intake affects blood cholesterol levels, yet jumping to conclusions on the basis of insuffi cient evidence has caused a considerable scare. (Sutherland, 1992, p. 184)