DASH Diet - What is the DASH Diet?

The DASH diet (Dietary Approaches to Stop Hypertension) is a diet promoted by the National Heart (part of the NIH, a United States government organization) to control hypertension.

A major feature of the plan is limiting intake of sodium, and it also generally encourages the consumption of nuts, whole grains, fish, poultry, fruits and vegetables while lowering the consumption of red meats, sweets, and sugar. It is also "rich in potassium, magnesium, and calcium, as well as protein and fiber."

According to the National Heart (NHLBI), citing data from 2002 , “The relationship between BP and risk of cardiovascular disease (CVD) events is continuous, consistent, and independent of other risk factors.

The higher the BP, the greater is the chance of heart attack, heart failure, stroke, and kidney disease.

For individuals 40–70 years of age, each increment of 20 mm Hg in systolic BP (SBP) or 10 mm Hg in diastolic BP (DBP) doubles the risk of CVD across the entire BP range from 115/75 to 185/115 mm Hg.”.

The prevalence of hypertension led the U.S. Institute of Health (NIH) to propose funding to further research the role of key nutrients in the diet.

In 1992 the NHLBI directed five of the most well-respected medical research centers in different cities across the U.S. to conduct the largest and most detailed research study to date.

The DASH study involved teams of physicians, nurses, nutritionists, statisticians and research coordinators working in a cooperative venture in which participants were selected and studied in each of the these five research facilities.

The chosen facilities and locales for this multi-center study were (1) Johns Hopkins University in Baltimore, Maryland, (2) Duke University Medical Center in Durham, North Carolina, (3) Kaiser Permanente Center for Health Research in Portland, Oregon, (4) Harvard School of Public Health in Boston, Massachusetts and (5) Pennington Biomedical Research Center in Baton Rouge, Louisiana.

The DASH trials were designed and carried out as a multi-center, randomized, outpatient feeding study with the purpose of testing the effects of dietary patterns on blood pressure.

The standardized multi-center protocol was one of the unique features of the DASH diet.

Another unique feature of the DASH diet and design was the foods and menu were chosen based on conventionally consumed food items which would be easily adopted by the general public if results were positive.

The initial DASH study was begun in August 1993 and ended in July 1997.

Contemporary epidemiological research had concluded that dietary patterns with high intakes of certain minerals and fiber were associated with low blood pressures. The nutritional conceptualization of the DASH meal plans was based in part on this research.

Two experimental diets were selected for the DASH study and compared with each other, and with a third: the control diet. The control diet was characteristically low in potassium, calcium, magnesium and fiber.

Moreover, the control diet also featured a fat and protein profile consistent with current or contemporary dietary regimens (a “typical American diet”).

The first experimental diet was an idealized ‘good’ diet consisting of fruits and vegetables but otherwise similar to the control diet (a “fruits and vegetables diet”), with the exception of fewer snacks and sweets.

Magnesium and Potassium levels were close to the 75th percentile of U.S. consumption in the fruits-and-vegetables diet, which also featured a high fiber profile.

The second experimental diet combined elements of the previous two (control and fruits-and-vegetables)—this diet has been called "the DASH Diet”.

The Dash diet (or combination diet) was rich in potassium, magnesium and calcium—a nutrient profile roughly equivalent with the 75th percentile of U.S. consumption.

The DASH diet was also high in fruits, vegetables & low fat dairy foods, and also rich in fiber and protein (18%).

The combination or ‘DASH’ diet was also high in whole grains, poultry, fish and nuts while being low in fat and red meat content, sweets and sugar-containing beverages.

The DASH diet was also focused on providing liberal amounts of key nutrients thought to play a part in lowering blood pressure, based on past medical studies.

The DASH diet was designed to be a whole-food diet, low in processed or refined sugars and high in complex carbohydrates.

One of the unique features of the DASH diet design is that dietary patterns rather than single nutrients were being tested. However, it was thought that the richness of complex-carbohydrates would help to minimize the often abrupt increases in blood sugar and insulin levels associated with hardening of the arteries, mood swings and weight gain.

Equally important, the DASH diet features a high quotient of anti-oxidant rich foods thought to retard or prevent chronic health problems including cancer, heart disease and stroke.

People were screened for the study, out of which were ultimately chosen 459 participants whose demographic characteristics most closely resembled the target population and study requirements.

The sample population consisted of healthy men and women with an average age of 46, with systolic blood pressures of less than 160 mm Hg and diastolic blood pressures within 80 to 95 mm Hg.

African-American and other minority groups were planned to comprise 67% of the study sample, with 49% of the sample being female.

Indeed, due to the exceptional burden of high blood pressure in minority populations, especially among African-Americans, a major goal of the trial was to recruit enough ethnic minorities to constitute two thirds of the target sample.

Participants ate one of the three aforementioned dietary patterns in 3 separate phases of the trial, including (1) Screening, (2), Run-in and (3) Intervention.

In the screening phase, participants were screened for eligibility based on the combined results of blood pressure readings and a Stanford 7-Day Physical Activity Recall questionnaire.

In the 3 week run-in phase, each subject was given the control diet for 3 weeks, had their blood pressure measurements taken on each of five separate days, gave one 24-hour urine sample and completed a questionnaire on symptoms.

At this point the subjects were each randomly assigned to one of the three diets outlined above, to begin at the start of the 4th week.

The intervention phase followed next; this was an 8-week period in which the subjects followed the diet they had each been randomly assigned to.

Blood pressures and urine samples were collected again during this time together with symptom & physical activity recall questionnaires.

The first group of study subjects began the run-in phase of the trial in September 1994 while the fifth and final group began in January 1996.

Each of the three diets contained the same 3 grams (3,000 mg) of sodium. Participants were also given two packets of salt, each containing 2,000 mg of sodium, for discretionary use.

Alcohol was limited to no more than two beverages per day, and caffeine intake was limited to no more than three caffeinated beverages.

The DASH study showed that dietary patterns can and do affect blood pressure in the normal to moderately hypertensive adult population (systolic < 180 mm Hg & diastolic of 80 to 95 mm Hg).

Respectively, the DASH or “combination” diet lowered blood pressures by an average of 5.5 and 3.0 mm Hg for systolic and diastolic, compared to the control diet.

The minority portion of the study sample and the hypertensive portion, from baseline, both showed the largest reductions in blood pressure from the combination diet against the control diet.

The hypertensive subjects experienced a drop of 11.4 mm Hg in their systolic and 2.1 mm Hg in their diastolic phases.

The fruits-and-vegetables diet was also successful, although it produced more modest reductions over the control diet (2.8 mm Hg systolic and 1.1 mm Hg diastolic).

In the subjects with and without hypertension, the combination diet effectively reduced blood pressure more than the fruits-and-vegetables diet or the control diet did.

The data indicated that reductions in blood pressure occurred within two weeks of subjects’ starting their designated diets, which were favorable results[6, and that the results were generalizable to the target sample of the U.S. population.

Side effects were negligible, but the NEJM study reports that constipation was evidently a problem for some of the subjects.

At the end of the intervention phase, 10.1, 5.4 & 4.0 percent of the subjects reported this problem for the control, fruits-and-vegetables and combination diets, respectively. Apart from only one subject (on the control diet) who was suffering from cholecystitis, other gastrointestinal symptoms had a low rate of incidence.

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The DASH-Sodium study

The DASH-Sodium study was conducted following the end of the original DASH study to determine whether the DASH diet could produce even better results if it were low in salt.

Primarily the researchers were interested in gaining more insight into the effect of sodium reduction when combined with the DASH diet.

Design of the trials for the DASH-Sodium study were conducted and the trials took place from September 1997 through November 1999.

Like the previous study, it was based on a large sample (412 participants) and was a multi-center, randomized, outpatient feeding study.

The participants were adults with pre-hypertension or stage 1 hypertension (average systolic of 120 to 159 mm Hg & average diastolic of 80 to 95 mm Hg) and were randomly assigned to one of two diet groups.

The two randomized diet groups were the DASH diet and a control diet that mirrored an “average American diet”, and which was somewhat low in key nutrients such as potassium, magnesium and calcium.

After being assigned to one of these two diets, and within their assignment the participants ate foods differentiated by 3 distinct levels of sodium content, corresponding to 3,000 mg, 2,400 mg or 1,500 mg/day (hi, intermediate or low), in random order, for 30 consecutive days.

During the two week run-in phase, all participants ate the high sodium control diet.

The 30 day intervention phase followed, in which subjects ate their assigned diets at each of the aforementioned sodium levels (high, intermediate and low) in random order, in a crossover design.

During the 30 day dietary intervention phase, each participant therefore consumed his or her assigned diet (either DASH or control) at all three sodium levels.

The primary outcome of the DASH-Sodium study was systolic blood pressure at the end of the 30 day dietary intervention periods. The secondary outcome was diastolic blood pressure.

The DASH-Sodium study confirmed that reductions in sodium intake correlated with significantly lower systolic and diastolic blood pressures in both control and DASH diets.

Study results indicate that the quantity of dietary sodium in the control diet was twice as powerful in its effect on blood pressure as it was in the DASH diet.

Importantly, the control diet sodium reductions from intermediate to low correlated with greater changes in systolic blood pressure than those same changes from high to intermediate (change equal to roughly 40 mmol per day, or 1 gram of sodium).

As stated by Sacks, F. et al., reductions in sodium intake by this amount per day correlated with greater decreases in blood pressure when the starting sodium intake level was already at the U.S. recommended dietary allowance, than when the starting level was higher (higher levels are the actual average in the U.S.).

These results led researchers to postulate that the adoption of a national lower daily allowance for sodium than the currently held 2,400 mg could be based on the sound scientific results provided by this study.

The DASH diet and the control diet at low salt levels were both successful in lowering blood pressure, but the largest reductions in blood pressure were obtained by eating a combination of these two (i.e., a low-salt version of the DASH diet).

The effect of this combination at a sodium level of 1,500 mg/day was an average blood pressure reduction of 8.9/4.5 mm Hg (systolic/diastolic).

The hypertensive subjects experienced an average reduction of 11.5/5.7 mm Hg.

The DASH-sodium results indicate that low sodium levels correlated with the largest reductions in blood pressure for participants at both normative and hypertensive levels with the hypertensive participants showing the greatest reductions in blood pressure overall.

Moreover, the African-American study participants showed particularly significant reductions in blood pressure.

This article is licensed under the Creative Commons Attribution-ShareAlike License. It uses material from the Wikipedia article on "DASH diet" All material adapted used from Wikipedia is available under the terms of the Creative Commons Attribution-ShareAlike License. Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.