Sarah Samaan - DASH Diet For Dummies

The scientists set up their research as a randomized, controlled trial, which means they followed strict scientific principles to limit any deviation from the study, provided all the meals, and monitored the research subjects very closely.

For their first experiment, the DASHers recruited 459 brave men and women, all of whom had borderline to high blood pressure. To be included, the participants’ baseline systolic pressure couldn’t be higher than 160, and the diastolic readings could range from 80 to 95. No one was on blood pressure medication.

Women have often been under-represented in medical studies, but the DASH researchers were smart enough to avoid that mistake. About half of those enrolled were female. The researchers also made sure to enroll a large number of African-American participants, about 60 percent of the total group, because they knew that high blood pressure is especially prevalent in African Americans (currently about 46 percent, compared to around a third of whites, Hispanics, and Asians).

DASH hasn’t been studied on a large scale in Hispanics, Asians, or other ethnic groups, but small studies have found similar benefits in Hispanic Americans and in Chinese men and women, and it is easily adaptable for a wide variety of dietary preferences. No matter who you are or where you’re from, if you have high blood pressure or are at risk for it, you owe it to yourself to check out the DASH diet.

The people studied were also diverse in other ways. Some were low-income; others middle-to-upper-middle class. Their average age was 44, but the range of ages was wide. Most were overweight, but some were obese.

After all the subjects were recruited and screened, the fun began. In what was termed the run-in phase, everyone was given a standardized control diet for the first three weeks, which included all their meals and snacks. Next, each person was randomly assigned to spend eight weeks on one of the three experimental diets: control, fruits and vegetables, or DASH. All the food was prepared for them to keep everything as strictly regimented as possible.

Throughout the study, researchers measured the participants’ blood pressures at strict intervals, administered a questionnaire about symptoms and activity, and did urine tests to objectively assess potassium, magnesium, calcium, and protein intake (and to be sure everyone was onboard with the assigned diets).

In DASH, researchers kept the subjects’ calories constant throughout the study to keep body weight stable so they could evaluate the effect of the diet itself. Because they knew that weight loss lowers blood pressure, they had no reason to reinvent the wheel. (In reality, it’s easy to cut calories and lose weight on DASH, but that wasn’t the point of this particular study.)

The initial DASH study also kept sodium intake constant at about 3,000 milligrams per day. Although 3,000 milligrams is a pretty high daily dose of sodium, it’s still somewhat lower than the typical 3,400 milligrams found in a standard Western diet. To keep it simple, the DASH group wanted to first determine whether certain foods people eat may have an impact on blood pressure, regardless of salt.

The control diet: Because the control diet was designed to mimic a typical American diet, it included a hefty quantity of fat, plenty of meat, paltry amounts of fiber, and meager servings of fruits and vegetables. It was fairly low in potassium, magnesium, and calcium. In short, it was the type of diet that keeps cardiologists in business.

The fruits-and-vegetables diet: The fruits-and-vegetables diet group included on average more than 5 servings of fruit and more than 3 servings of vegetables each day, or nearly 2½ times the amount of plant-based food as the control diet. As a result, this diet supplied more than three times the amount of fiber as the control diet, and much more potassium and magnesium as well. This particular diet wasn’t designed to test a vegetarian diet, so it included about the same amount of fat and the same amount of meat, poultry, and fish as the control diet. However, it included one-third the number of snacks and sweets.

The DASH diet: In addition to incorporating the added fruits and vegetables, the DASH diet group included 2 servings of low-fat dairy per day, something neither of the other diets did. DASH dieters received about one-third the amount of meat as the other groups but similar quantities of poultry and a little more fish. Added fats, such as oils and salad dressing, were reduced by more than half, and sweets and snacks were severely curtailed.

The results of the DASH study were conclusive: A reduced-fat diet rich in low-fat dairy, along with plenty of fruits and vegetables, can lower blood pressure substantially. Compared with the control diet, the fruits-and-vegetables diet dropped systolic pressure 2.8 points and diastolic 1.1 points. That doesn’t sound very impressive, but it’s meaningful in terms of stroke and heart disease risk reduction. The DASH diet was more powerful, lowering systolic pressure by 5.5 points and diastolic by 3 points.

More important, in those people diagnosed with hypertension at the beginning of the study, blood pressure fell by an average of 11.4 points systolic and 5.5 points diastolic, which is on par with the results you would expect from medical therapy. The improvement happened quickly, with results seen within two weeks on the diet, and improvement was seen across race and gender. Speaking of gender, DASH was actually somewhat more effective in women over the age of 45 compared to men. (Other studies focusing on salt restriction have also found that women do at least as well as their male counterparts over the long term, substantially reducing their risk for stroke and heart disease.)

Some people may worry that a plant-heavy diet could cause intestinal upset, but the DASH researchers found the opposite. In fact, constipation was reported in 10 percent of those on the typical Western-style control diet but in only 4 percent of those on DASH.

Overall, the researchers estimated that the drop in blood pressure seen by simply following the DASH diet had the power to reduce heart disease by 15 percent and cut the incidence of stroke by 27 percent. That’s a lot of lives saved and misery prevented.

Sodium consumption in the United States and around the world has skyrocketed over the past few decades. This growth can be traced directly to a growing reliance on fast foods, restaurant meals, and processed foods. In the United States, the average diet includes about 3,400 milligrams of sodium every day, yet the human body requires a mere 500 milligrams for normal function.

Overload your system with salt, and your blood pressure is likely to rise. Why? Because sodium causes the body to retain water, which in turn affects the kidneys’ ability to properly regulate blood pressure. High sodium may also have directly harmful effects on the arteries that feed the heart, kidneys, and other vital organs. What’s worse, a low potassium diet tends to cause the body to retain salt, aggravating the problem. Potassium comes chiefly from fruits, vegetables, and milk. The fact that DASH is relatively high in these natural sources of potassium is probably one reason that it works so well.