To assess the impact of a food-based intervention on blood pressure (BP) in free-living South African men and women aged 50–75 years, with drug-treated mild-to-moderate hypertension.

A double-blind controlled trial was undertaken in eighty drug-treated mild-to-moderate hypertensive subjects randomised to an intervention (n 40) or control (n 40) arm. The intervention was 8-week provision of six food items with a modified cation content (salt replacement (SOLO™), bread, margarine, stock cubes, soup mix and a flavour enhancer) and 500 ml of maas (fermented milk)/d. The control diet provided the same quantities of the targeted foods but of standard commercial composition and 500 ml/d of artificially sweetened cooldrink.

The intervention effect estimated as the contrast of the within-diet group changes in BP from baseline to post-intervention was a significant reduction of 6·2 mmHg (95 % CI 0·9, 11·4) for systolic BP. The largest intervention effect in 24 h BP was for wake systolic BP with a reduction of 5·1 mmHg (95 % CI 0·4, 9·9). For wake diastolic BP the reduction was 2·7 mmHg (95 % CI −0·2, 5·6).

Modification of the cation content of a limited number of commonly consumed foods lowers BP by a clinically significant magnitude in treated South African hypertensive patients of low socio-economic status. The magnitude of BP reduction provides motivation for a public health strategy that could be adopted through lobbying of the food industry by consumer and health agencies.