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DASH stands for the Dietary Approaches to Stop Hypertension. The DASH diet is based on DASH Study results published in 1997. The study showed that a diet rich in fruits, vegetables and low fat dairy foods, with reduced saturated and total fat could substantially lower blood pressure. It is the diet recommended by the National Heart, Lung and Blood Institute (part of the National Institute of Health) for lowering blood pressure.
High blood pressure affects about one in four in the United States and United Kingdom and is defined as blood pressure consistently above 140/90 mmHg. The top number, 140, is the systolic pressure exerted by the blood against the arteries while the heart is contracting. The bottom number, 90, is the diastolic pressure in the arteries while the heart is relaxing or between beats. The concern is the higher the blood pressure, the greater the risk for developing heart and kidney disease and stroke. High blood pressure is known as the silent killer as it has no symptoms or warning signs.
The DASH study by the National Lung, Blood and Heart Institute (NHLBI), published in the New England Journal of Medicine in 1977, was the first study to look at the effect a whole diet rich in potassium, magnesium and calcium foods, not supplements, had on blood pressure.
The study involved 459 adults with and without high blood pressure. Systolic blood pressures had to be less than 160 mm Hg and diastolic pressures 80 to 95 mm Hg. Approximately half the participants were women and 60% were African Americans. Three eating plans were compared. The first was similar to a typical American diet—high in fat (37% of calories) and low in fruit and vegetables. The second was the American Diet, but with more fruits and vegetables. The third was a plan rich in fruits, vegetables, and low fat dairy foods and low fat (less than 30% of calories). It also provided 4,700 mg potassium, 500 mg magnesium and 1,240 mg calcium per 2,000 calories. This has become known as the DASH diet. All three plans contained equal amounts of sodium, about 3,000 mg of sodium daily, equivalent to 7 g of salt. This was approximately 20% below the average intake for adults in the United States and close to the current salt recommendations of 5–6 g. Calorie intake was adjusted to maintain each person”s weight. These two factors were included to eliminate salt reduction and weight loss as potential reasons for any changes in blood pressure. All meals were prepared for the participants in a central kitchen to increase compliance on the diets.
Results showed that the increased fruit and vegetable and DASH plans lowered blood pressure, but the DASH plan was the most effective. It reduced blood pressure by 6 mmHg for systolic and 3 mmHg for diastolic, those without high blood pressure. The results were better for those with high blood pres-sure–the drop in systolic and diastolic was almost double at 11 mmHg and 6 mmHg respectively. These results showed that the DASH diet appeared to lower blood pressure as well as a 3 g salt restricted diet, but more importantly, had a similar reduction as seen with the use of a single blood pressure medication. The effect was seen within two weeks of starting the DASH plan, which is also comparable to treatment by medication, and continued throughout the trial. This trial provided the first experimental evidence that potassium, calcium, and magnesium are important.
(Illustration by GGS Information Services/Thomson Gale.)
dietary factors in determinants of blood pressure than sodium alone.
The original DASH plan did not restrict sodium. As a result, a second DASH-Sodium trial from 1997-1999 (published 2001) looked at the effect the DASH diet with different sodium levels (3,300, 2,300 or 1,500mg) had on blood pressure. This is known as the DASH-sodium diet. The highest amount recommended by the 2005 U.S. dietary guidelines is 2,300 mg. The amount recommended by the Institute of Medicine, as a minimum to replace the amount lost through urine and to achieve a diet that provides sufficient amounts of essential nutrients, is 1,500 mg. The results showed that the combined effect of a lower sodium intake with the DASH diet was greater than just the DASH diet or a low salt diet. Like earlier studies, the greatest effect was with the lower sodium intake of 1,500mg (4 g or 2–3 tsp of salt), particularly for those without hypertension. For this group, the systolic dropped about 7.1 mmHg and the diastolic about 3.7 mmHg. However, the reduction in blood pressure for hypertensives was 11.5 mmHg for systolic and 5.7 mmHg for diastolic, quite similar to the reductions seen with the DASH diet.
The diet is based on 2,000 calories with the following nutritional profile:
These percentages translate into more practical guidelines using food group servings.
sunflower). Saturated and trans fat consumption should be decreased.
An example breakfast menu is: cornflakes (1 cup) with 1 tsp sugar, skimmed milk (1 cup), orange juice (1/2 cup), a banana and a slice of whole wheat bread with 1-tablespoon jam. Suggested snacks during the day include dried apricots (1/4 cup), low fat yogurt (1 cup) and mixed nuts (1.5 oz, 40g).
These guidelines are available in the National Institutes of Health (NIH) updated booklet “Your Guide to Lowering Your Blood Pressure with DASH”, which also provides background information, weekly menus, and recipes.
Although the DASH diet provides two to three times the amount of some nutrients currently consumed in the average American diet, the recommendations are not dissimilar to the 2005 U.S. dietary guidelines (United States Department of Agriculture (USDA) and U.S. Department of Health and Human Services). It also resembles the USDA Food Guide Pyramid, which advocates low-fat dairy products and lean meats. The main difference is the emphasis on more fruit and vegetables servings, 8 to 10 as opposed to the 5 to 13 as in the U.S. dietary recommendations. In addition, it separates nuts, seeds, and beans from the meat, fish, and poultry food groups and recommends four to five weekly servings of nuts, seeds, and dry beans.
The Dash diet was not designed for weight loss but it can be adapted for lower calorie intakes. The NIH booklet provides guidelines for a 1,600-calorie diet. Vegetarians can also use the diet, as it is high in fruits, vegetables, beans, seeds, and low-fat dairy, which are the main sources of protein in a vegetarian diet.
The DASH meal plan is a healthy diet recommended for those with and without high blood pressure.
The DASH diet may lower blood pressure as much as taking medication, but without the risk of unwanted side effects. The dietary changes can also have immediate effects comparable with drug therapy. A blood pressure reduction of the degree seen in the DASH study is estimated to reduce the incidence of coronary artery disease by 15% and stroke by 27%.
Adding high fiber foods to the diet should be done gradually to avoid side effects such as gas, bloating, and diarrhea. It is important to increase fluid at the same time, as fiber draws water into the bowel. High fiber with inadequate fluid can cause hard stools and constipation.
Increasing fruits and vegetables increases the potassium content of the diet. For healthy people with normal kidney function, a higher potassium intake from foods does not pose a risk as excess potassium is excreted in the urine. However, individuals whose urinary potassium excretion is impaired, such as those with end-stage renal disease, severe heart failure, and adrenal insufficiency may be at risk of hyperkalaemia (high levels of potassium in the blood). Hyperkalaemia may cause cardiac arrthymias (irregular heart beat), which could be serious. Some common drugs can also decrease potassium excretion. Individuals at risk should consult a doctor before staring the DASH diet, as higher potassium intakes in the form of fruit and vegetables may not be suitable. Care should also be taken with potassium containing salt substitutes.
Currently, there are no known risks associated with the DASH diet. However, the long-term effects of the diet on morbidity and mortality are still unknown.
Studies over the years have suggested high intakes of salt play a role in the development of high blood pressure so dietary advice for the prevention and lowering of blood pressure has focused primarily on reducing sodium or salt intake. A 1989 study looked at the response an intake of 3-12 g of salt per day had on blood pressure. The study found that modest reductions in salt, 5-6 g salt per day caused blood pressures to fall in hypertensives. The best effect was seen with only 3 g of salt per day with blood pressure falls of 11 mmHg systolic and 6 mmHg diastolic. More recently, the use of low salt diets for the prevention or treatment of high blood pressure has come into question. The Trials of Hypertension Prevention Phase II in 1997 indicated that energy intake and weight loss were more important than the restriction of dietary salt in the prevention of hypertension. A 2006 Cochrane review, which looked at the effect of longer-term modest salt reduction on blood pressure, found that modest reductions in salt intake could have a significant effect on blood pressure in those with high blood pressure, but a lesser effect on those without. It agreed that the 2007 public health recommendations of reducing salt intake from levels of 9-12 g/day to a moderate 5-6 g/day would have a beneficial effect on blood pressure and cardiovascular disease.
The effectiveness of the DASH diet for lowering blood pressure is well recognized. The 2005 Dietary Guidelines for Americans recommends the DASH Eating Plan as an example of a balanced eating plan consistent with the existing guidelines and it forms the basis for the USDA MyPyramid. DASH is also recommended in other guidelines such as those advocated by the British Nutrition Foundation, American Heart Association, and American Society for Hypertension.
Although results of the study indicated that reducing sodium and increasing potassium, calcium, and magnesium intakes play a key role on lowering blood pressure, the reasons why the DASH eating plan or the DASH-Sodium had a beneficial affect remains uncertain. The researchers suggest it may be because whole foods improve the absorption of the potassium, calcium and magnesium or it may be related to the cumulative effect of eating these nutrients together than the individual nutrients themselves. It is also speculated that it may be something else in the fruit, vegetables, and low-fat dairy products that accounts for the association between the diet and blood pressure.
The Salt Institute supports the DASH diet, but without the salt restriction. They claim that the DASH diet alone, without reduced sodium intake from manufactured foods, would achieve the desired blood pressure reduction. Their recommendation is based on the fact that there are no evidence-based studies supporting the need for dietary salt restriction for the entire population. The Cochrane review in 2006 showed that modest reductions in salt intake lowers blood pressure significantly in hypertensives, but a lesser effect on individuals with normal blood pressure. Restriction of salt for those with out hypertension is not recommended.
Researchers have evaluated other dietary modifications, such as the role of potassium, magnesium, and calcium on blood pressure. Substantial evidence shows individuals with diets high in fruits and vegetables and, hence, potassium, magnesium, and calcium, such as vegetarians, tend to have lower blood pressures. However, in studies where individuals have been supplemented with these nutrients, the results on their effects on blood pressure have been inconclusive.
There is some debate on whether patients can follow the diet long-term. The 2003 premier study (a multi-center trial), which included the DASH diet when looking at the effect of diet on blood pressure, found that the DASH diet results were less than the original study. This difference is thought to be because in the DASH study participants were supplied with prepared meals, while participants on the premier study prepared their own foods. As a result, only half the fruit and vegetable intake was achieved in the premier study, which affected the overall intakes of potassium and magnesium. The researches concluded that compliance to the DASH diet in the long term is questionable, but agreed that patients should still be encouraged to adopt healthy interventions such as the DASH diet, as it does offer health benefits.
In terms of heart health, the Dash diet lowered total cholesterol and LDL cholesterol, but it was associated with a decrease in high-density lipoprotein (HDL), the “good” cholesterol. Low HDL levels are considered a risk factor for coronary heart disease (CHD) while high levels are thought to be protective of heart disease. The decrease was greatest in individuals who started with a higher level of the protective HDL. Researchers agree that the reasons for the decrease in HDL levels needs further review, but concluded that the overall effects of the DASH diet are beneficial to heart disease.
While long term health effects of the DASH diet are yet to be established, the diet closely resembles the Mediterranean diet, which has been shown to have other health benefits including a reduced risk for heart disease and cancer rates. It is thought that the DASH diet is likely to offer similar health benefits.
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American Heart Association. 7272 Greenville Avenue, Dallas, TX 7523 USA. Telephone: (800) 242-8721. Website: <http://www.americanheart.org/>.
American Medical Association. 515 N. State Street, Chicago, IL 60610 USA. Telephone: (800) 621-8335. Website: <http://www.ama-assn.org/>.
American Society for Hypertension. 148 Madison Avenue, Fifth Floor, New York, NY 10016 USA. Telephone: (212) 696-9099. Website: <http://www.ash-us.org/>.
British Heart Foundation (BHF). 14 Fitzhardinge Street, London W1H 6DH, UK. Website: <http://www.bhf.org.uk/>
British Nutrition Foundation. High Holborn House, 52-54, High Holborn, London WC1V 6RQ, UK. Telephone: 020 7404 6504. Website: <http://www.nutrition.org.uk/>.
The Cochrane Collaboration. Summertown Pavilion, 18-24 Middle Way, Oxford, Oxfordshire OX2 7LG UK. Telephone: 44 1865 310138. Website: <http://www.cochrane.org/>.
Food Standards Agency UK (FSA). Eat well Be well, Healthy Heart Aviation House, 125 Kingsway, London WC2B.
6NH UK. Website: <http://www.eatwell.gov.uk/>.
National Lung, Blood and Heart Institute (NHLBI). health information centre, PO Box 30105, Bethesda MD 20824-0105. Telephone: (301) 592-8573. USA. Website: <http://www.nhlbi.nih.gov/>.
Salt Institute. 700 N. Fairfax Street, Suite 600 Fairfax Plaza, Alexandria, VA 22314-2040 USA. Website: <http://www.saltinstitute.org/>.
Tracy J. Parker, RD