The Science Behind the DASH Eating Plan

The DASH study included 459 adults, some with and some without confirmed high blood pressure. The study compared three diets, each containing 3,000 milligrams (mg) of sodium per day:

• Typical American diet
• Typical American diet plus more fruits and vegetables
• DASH diet

The study provided all foods and beverages to participants. None of the diets were vegetarian or used specialty foods. After 8 weeks, participants who consumed more fruits and vegetables plus a typical American diet or those on the DASH diet had lower blood pressure than those who followed a typical American diet alone. However, the participants on the DASH diet had the greatest effect of lowering their high blood pressure.

Follow-up reports from the DASH trial showed that in addition to improving blood pressure, the DASH diet also lowered LDL cholesterol levels. Both high blood pressure and high blood levels of LDL cholesterol are major risk factors for cardiovascular disease.

This study included 412 adults who followed either a typical American diet or the DASH diet. The study provided all foods and beverages to participants for 1 month. Their daily sodium intake levels were either high, at 3,300 mg (which is similar to the current average U.S. daily sodium intake of about 3,600 mg); medium at 2,300 mg; or low at 1,500 mg.
The DASH-Sodium study made several findings:

• Reducing daily sodium lowered blood pressure for participants on either diet. However, the DASH diet plus the low sodium (1,500 mg or about half a teaspoon of salt) lowered blood pressure more than the typical American diet at all three daily sodium levels.
• Blood pressure decreased with each reduction of sodium.
• Reducing sodium intake and following the DASH diet is more beneficial for lowering blood pressure than following the DASH diet alone or reducing sodium alone.
• The benefits of a reduced sodium and DASH diet were observed in those with and without hypertension, women and men, regardless of race or ethnicity.

A follow-up report found that combining the DASH diet with sodium reduction benefited people who had higher than normal blood pressure readings. The report also found that people who started out with the highest blood pressure readings experienced the greatest benefits.

The OmniHeart study included 164 adults who had systolic blood pressure readings ranging from 120 to 159 millimeters of mercury (mm Hg) and diastolic blood pressure readings ranging from 80 to 99 mm Hg. The study compared the following three diets, each containing 2,300 mg of sodium per day:

• DASH diet alone
• DASH diet substituting 10% of total daily calories of carbohydrates with protein, with about half from plant-based proteins
• DASH diet substituting 10% of total daily calories of carbohydrate diet with unsaturated fat, mostly monounsaturated fat

The study provided all foods and beverages to participants, who followed each diet for 6 weeks with a 2- to 4- week period between each diet during which they ate their own foods. During the study, body weight of the participants did not change.

OmniHeart found that either variation of the DASH diet — by partially substituting carbohydrate with either protein or unsaturated fat for 10% of daily calories — reduced blood pressure and improved lipid levels more than the original DASH diet. The risk of heart disease was also lower for participants on the protein and unsaturated fat diets compared to the original DASH diet.

The OmniCarb trial included 163 adults who had overweight or obesity and who had systolic blood pressure readings ranging from 120 to 159 mm Hg and diastolic blood pressure readings ranging from 80 to 99 mm Hg. The study compared the following four DASH-like diets, each containing 2,300 mg of sodium per day:

• DASH diet high in carbohydrates with a high glycemic index
• DASH diet high in carbohydrates with a low glycemic index
• DASH diet low in carbohydrates with a high glycemic index
• DASH diet low in carbohydrates with a low glycemic index

The study provided all foods and beverages to participants, who followed each diet for 5 weeks with a 2-week period between each diet during which they ate their own foods. During the study, participants maintained a constant body weight.

OmniCarb found that diets with a low glycemic index did not improve blood pressure, blood cholesterol, or insulin resistance compared to diets with a high glycemic index. The study found that in the context of an overall DASH-like diet, using glycemic index to select specific foods to consume may not improve cardiovascular risk or insulin resistance.

The PREMIER trial included 810 participants who had systolic blood pressure readings ranging from 120 to 159 mm Hg and diastolic blood pressure readings ranging from 80 to 95 mm Hg. They were each assigned to one of three groups. Each group participated in a different program to lower blood pressure, lose weight, and improve health for 6 months:

• An advice-only program that did not include counseling on behavior changes
• An established treatment program that included counseling on behavior changes
• And established treatment plan that included both counseling and use of the DASH diet

Unlike the other studies listed above, the PREMIER trial did not provide food and beverages to participants.

PREMIER found that after 6 months, blood pressure levels declined in all three groups. The two groups that received counseling and followed a treatment plan had more weight loss than the advice-only group. However, participants who received counseling and followed the DASH diet had the greatest reductions in their blood pressure. The study results showed that people can lose weight and lower their blood pressure by following the DASH diet and increasing their physical activity.

The NHLBI continues to fund research on DASH that explores barriers to and opportunities for dietary changes. Research also explores the potential benefits of the plan for other health conditions, in addition to high blood pressure.

• A small study published in 2014 explored the potential benefits of the DASH eating plan for 90 participants with uncontrolled asthma and poor dietary habits. The group who followed the DASH eating plan experienced improvement in their asthma control. A new study funded by the NHLBI — Addressing Quality of Life, Clinical Outcomes, and Mechanisms in Uncontrolled Asthma Following the DASH Dietary Pattern (ALOHA) – is also testing whether following the DASH eating plan can improve asthma. One group will receive asthma education. The other will receive education and dietary counseling and will follow the DASH eating plan.
• An NHLBI-funded study uses a smartphone app to track the foods participants eat each day as they follow the DASH eating plan. Researchers are exploring digital health as a new way to improve eating habits and lower blood pressure.
• Researchers in an NHLBI-funded study are examining short-term positive benefits of the DASH diet on ongoing heart damage caused by injury, stress, and inflammation.