Fibre

causative relationship is suggested by the findings of Efrain Reisin and his colleagues who showed that even if salt intake is kept constant, overweight hypertensive subjects who diet successfully have significant reductions in blood pressure.5 More specifically, Pirjo Pietinen and fellow workers undertook a comprehensive review of studies relating animal fat intake to blood pressure elevation. It was found that in populations as disparate as those of Finland and the United States there was a positive relationship between a diet high in saturated and low in polyunsaturated fat on the one hand and blood pressure levels on the other.6 Conversely, other studies reviewed by these authors showed that increasing the P/S ratio was followed by a fall in blood pressure even if the total fat intake remained the same. The decline in systolic blood pressure ranged from 1 to 13 mmHg and up to 8 mmHg in the case of the diastolic. Switchback observations with reduction in P/S ratio were made in nine studies. In seven they resulted in an increase in systolic and diastolic pressures when the ratio was low.7 The findings of J M Iacono and co-workers were confirmatory. They found that a six-week reduction in dietary fat content from 42 to 25 per cent with an increase in the polyunsaturated-saturated ratio resulted in a reduction in both the systolic and the diastolic pressures of normotensive healthy adult volunteers. The total energy intake was unchanged during the observation period.8 Quantitatively, linoleic acid was the commonest polyunsaturated fatty acid in these diets. In experimental rats its administration has been found to have a diuretic effect, increasing sodium excretion, a precursor of blood pressure fall.9 In contrast, Pietinen and colleagues have reported animal studies indicating that diets deficient in linoleic acid are associated with blood pressure elevation.'0 In combination these observations indicate a linkage of hypertension with diets conducive to obesity and either high in saturated or low in unsaturated fats.