There are several things you can do to improve hypertension before needing medication. The most commonly mentioned are increased physical activity, weight loss, and a low sodium, low fat diet. The least mentioned is a high potassium diet. But there are a great many medical studies on high potassium foods and hypertension. The best known studies involve the Mediterranean diet and the DASH diet, both of which are high potassium diets.
A nice contemporary summary of the role of dietary therapy of hypertension can be found at N Engl J Med 2010; 362:2102-2112.
The studies on the DASH diet originally looked at hypertensives having one of three diets – a normal American diet, a diet with lots of fruits and vegetables, and one with fruits and vegetables as well as low fat dairy and low saturated and total fat. Sodium intake and body weight were kept unchanged. After 8 weeks, the fruit and vegetable rich diet showed lower systolic blood pressure by 7.2 mm Hg and diastolic by 2.8. The one with dairy and reduced fat showed a lowering of systolic pressure by 11.4 and diastolic by 5.5.
A second DASH study looked at lower salt intake. They were on a regular American diet or the DASH diet that included dairy and low fat. The groups were divided into diets that were also either high, medium or low in sodium (3.5, 2.3, or 1.2 gm per day) for a month. The lower the sodium intake was, the lower the blood pressure was. Systolic pressure was lowered by 1.6 mm Hg for the 2.3 gm per day, and an additional 5.1 mm Hg for the 1.2 gm per day. Overall the systolic blood pressure was lowered from 143 on the typical American diet to 128 on the lowest sodium DASH diet.
Having sodium intake below 1500mg per day is considered ideal for an adult. Reducing dietary salt reduces the amount of sodium the kidney has to get rid of to maintain normal blood volume, which is one factor helping to keep blood pressure normal.
To find the effect of protein and unsaturated fat on blood pressure, another DASH diet study was done with fewer carbohydrates than the usual DASH diet. The control group was on a DASH diet with slightly more carbohydrates. For the experimental groups, one group was put on a diet higher in protein and another group was put on a diet higher in unsaturated fat. Both groups showed lower blood pressure. The higher protein group reduced their systolic pressure by 3.5 mm Hg and diastolic by 2.4 mm Hg. The unsaturated fat group reduced these pressures by 2.9 and 1.9 compared to the normal DASH.
So at present, the best diet to improve or avoid hypertension appears to be a diet with high potassium foods, low amounts of sodium, low fat dairy, unsaturated fats, reduced amounts of carbohydrates and more protein. A list of tables showing high potassium foods and the amount of potassium they contain can be found here.