1. Diets used to reduce sodium intake often involve changes in fats and fibre which might themselves affect blood pressure and/or lipid metabolism. To evaluate the relative importance of these dietary changes for the management of hypertension we have studied the independent and additive effects of sodium restriction (60 mmol/day) and a low fat (30% energy), high P/S ratio (1.0), high fibre (30–50 g/day) ‘cholesterol lowering’ diet.
2. Ninety-five hypertensives entered a four group parallel study with a factorial design. Following 5 weeks familiarization subjects [BP range 109/66–168/105 mmHg] were randomly assigned to either a ‘low sodium, cholesterol lowering’ diet or a ‘low sodium, cholesterol maintaining’ diet. Half the subjects in each group were then assigned to 100 mmol/day NaCl supplement and the remainder to placebo. These diets were continued for 8 weeks. Seventy-nine of the 91 hypertensives who completed the study were on antihypertensive therapy throughout.
3. Mean urinary sodium excretion decreased from 137 (54 mmol/day (n= 43) at baseline (B) to 52 (32) mmol/day (n= 45, P= 0.0001) during intervention (I) in the low sodium groups and remained unchanged in the groups which received slow sodium (B = 129 , n= 43; I = 134 , n= 42). Diet record and plasma fatty acid analysis confirmed that the dietary aims of the study were achieved.
4. Sodium restriction reduced supine and standing systolic BP by a mean (± s.e.m.) of 6±2 and 6±4 mmHg, respectively (P<0.005). The low fat/high fibre diet had no independent or additive effect on blood pressure reduction but reduced total and LDL cholesterol by an average of 0.74 and 0.59 mmol/L, respectively (P<0.0001).
5. In terms of reducing overall risk of cardiovascular disease, diets which combine sodium restriction with measures to reduce LDL cholesterol would appear optimal.