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DASH stands for Dietary Approaches to Stop Hypertension. Hypertension or high blood pressure has been on the rise in the US for the past 50 years.

The continued increase of hypertension led the National Institutes of Health to propose funding for research that would study the impact of dietary patterns on blood pressure.

In 1992, the National Heart, Lung and Blood Institute worked closely with five prestigious medical research centers in the US to design and carry out the largest and most detailed study ever conducted called “The DASH study.”

The DASH study was uniquely based on foods that the average person could buy at a local grocery store thus making it easy for anyone to implement.

The DASH study

The first DASH study began in 1993 and ended in July 1997. The study compared two experimental diets with one control diet. Each of the 459 screened participants were randomly selected to participate in one of three groups. They were instructed to follow the dietary pattern of that group for eight weeks in which time their blood pressure would be regularly checked.

The two experimental groups included:

Experimental diet group 1 – Fruits and vegetables diet

Other than a high consumption of fruits and vegetables this group was to eat the typical American diet with fewer sweets and snacks. Their fiber content was high and their magnesium and potassium levels were similar to 75% of people in the US.

Experimental diet group 2 – The DASH diet

This group was to consume a high intake of fruits, vegetables and low-fat dairy. Fat content was low and protein and fiber levels were high. This diet was rich in magnesium, potassium, calcium, fish, poultry, whole grains and nuts. The consumption of red meats, sweets and sweetened drinks was low. (This diet intentionally included foods that would reduce blood pressure. It also contained a lot of antioxidant rich foods).

Control group – The Control diet

This group was to consume food that was typical of the American diet - low in potassium, calcium, fiber and magnesium and high in protein and fat.

The results of the DASH study

The results of the DASH study proved that dietary patterns do affect people with moderate to severe hypertension.

The “fruits and vegetables” group experienced lower blood pressure but their decrease was not as significant as the DASH group. The participants in the DASH group that did not have hypertension experienced a decrease in blood pressure as well.

The study also showed that people with hypertension in the DASH diet group experienced a decrease in their blood pressure within only two weeks of starting the DASH diet.

The DASH sodium study

The second DASH study called “The DASH sodium study” was undertaken following “The DASH study” to see whether the DASH diet could lower blood pressure even more effectively if it were low in salt. The two main objectives of the “The DASH sodium study” were:

1. To study the effects of reduced sodium levels on the DASH diet

2. To study the effects of the DASH diet at three different sodium levels

The DASH sodium study was a large scale study that ran from 1997 to 1999. It involved 412 adult participants with stage 1 hypertension or prehypertension. There were two groups involved, the DASH diet group and the typical American diet group (the control diet group).

Each group was given a 30 day diet that included three different sodium levels: 3000 mg, 2400 mg and 1500 mg a day. Each diet was preceded by two weeks of high sodium control diet eating followed by 30 days of eating an assigned diet that randomized the sodium levels.

The results of the DASH sodium study

Both the DASH diet and the control diet were successful at lowering blood pressure at the lower salt levels but the biggest decrease in blood pressure was seen when the DASH diet was combined with low salt consumption of 1500 mg a day.

The results of this study also led researchers to propose that the national daily allowance of sodium be lowered. The U.S. Dietary Guidelines for Americans recommend 2300 mg of sodium per day or lower. 1500 mg of sodium a day is recommended for people who have high blood pressure.