DASH Diet Explained Simply

1. What It Is About

The DASH diet is not a medicine and not a powder, but a pattern for nutrition. The name comes from English and stands for Dietary Approaches to Stop Hypertension, that is, ways to influence blood pressure through nutrition. This pattern is investigated in two ways. In controlled studies one group receives a prescribed diet, another group a comparison diet; afterwards it is compared what has changed. In observational studies, by contrast, the question is how close a person’s usual diet is to this pattern and whether people with great closeness develop certain diseases less often.

Because it is a pattern, no quantity of a single substance can be stated. Instead, adherence to the specification is measured. This is called adherence. It is usually done via questionnaires in which points are awarded. It is important to know: a high score does not automatically mean that nutrition alone makes the difference. People who adhere strongly to the pattern often live more healthily in other respects as well. There are also modified forms of the pattern that are summarised in separate reviews.

2. What Studies Show

Blood pressure is the best investigated aspect. A summary of several controlled studies examined how the pattern affects adults with and without high blood pressure. This work involved 5,545 people 1. In the summarised studies blood pressure fell. Because several controlled studies with the same result are available, this point is considered well established.

Reviews also exist on the risk of certain diseases. One work examined the association between closeness to the DASH diet and diabetes and summarised data from 557,475 people 3. Another work addressed breast cancer and evaluated data from 449,273 women 2. In both works greater closeness to the pattern was associated with less frequent occurrence of the disease. Caution is required here: such observations show an association, not that the diet prevents the disease.

A review on lipid metabolism in blood is available for 3,562 people with overweight 4. A separate review exists for adolescents 7. Another work examined the components of the so-called metabolic syndrome, that is, the co-occurrence of elevated blood pressure, unfavourable blood-lipid values, overweight and impaired blood glucose 5. A summary on oxidative stress, that is, a burden on cells from aggressive oxygen compounds, is also available, although in 317 participants 6.

Works are also available on sleep, pregnancy, mood and liver values 10, 11, 8, 9. They are smaller, yet they provide indications of where further research is warranted.

3. What Remains Unclear

Individual controlled studies exist on cognition, that is, thinking and memory, and on the gut. A frequently cited work on lifestyle and cognitive performance did not test the DASH pattern alone. The association with periodontal disease likewise comes from a study that only surveyed people at one point in time; no effect can be inferred from this.

A second open point is the measurement of adherence. Questionnaires capture nutrition, health behaviour and education together. Whether actual nutrition can be depicted more objectively via substances in blood is a testable question. One work has described such a substance pattern in blood 12; whether it agrees with the questionnaire values remains open.

4. What This Means in Everyday Life

For classification this means: statements on blood pressure rest on a broad basis, statements on cognitive performance, the gut or the immune system rest on individual works. Anyone seeking information on the DASH diet therefore finds a well-investigated core and a periphery that is still growing.

The diet is a pattern for food selection over a longer period, not a single measure. In controlled studies the diet is prescribed; in everyday life it cannot be followed so strictly. Observational studies therefore show an association, not a tested effect. What would next need to be clarified: which measure depicts actual nutrition so that both types of studies become comparable? And which study tests the pattern alone, over a sufficiently long period, with a clear measure for cognitive performance?

All details with study numbers and sources: detailed page on the DASH diet. For children: DASH diet for children.