Responding to America’s Salt Obsession with Further DASH Diet Research
The Dietary Approaches to Stop Hypertension (DASH) diet came about because the 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.
Though a number of studies over the years have convincingly implicated salt as a bad guy when it comes to hypertension, the DASH researchers took on the challenge of directly comparing the impact of three different levels of sodium intake when added to a healthy, blood pressure–friendly DASH diet versus a less healthy, more typical control diet. Enter the DASH sodium study.
Participants included 412 adults with blood pressures higher than 120/80. More than half were women, more than half were black, and 40 percent had hypertension. Most were overweight.
The study included both the higher-fat, control, Western diet and the healthier DASH diet, and it tested three different levels of sodium intake: 3,450 milligrams, 2,300 milligrams, and 1,150 milligrams. Everyone started out on the high-sodium control diet for the first two weeks, and each was then randomly assigned to one of the two diets at one of the three sodium levels.
After 30 days, researchers changed the sodium dose such that each individual was tested at the low, intermediate, and high levels of sodium. As in the original DASH study, the researchers prepared all the participants’ food and kept their calories constant.
Not surprisingly, the lower the salt intake, the better the blood pressure. The impact of sodium was greater with the less-healthy control diet than it was in the DASH diet, but the DASH group had lower blood pressure overall. Cutting sodium was especially effective in people who had hypertension to begin with, indicating they were more sensitive to salt’s effects.
When pitted against the high-sodium control diet, the low-sodium DASH diet dropped systolic blood pressure by 11.5 points in people with hypertension. The effect was even greater (12.6 points) for black people. Women benefited more than men.
Even those without hypertension saw their blood pressures fall by about 7 points. Diastolic blood pressure dropped as well, but the effect wasn’t as dramatic, averaging about a 4.5-point difference between the high-sodium control diet and the low-sodium DASH group.
Because most people consistently eat too much salt, you may worry that a sudden change in sodium intake could cause side effects, even if, in the long run, it’s better for you. To the contrary: There were fewer headaches and no differences in any other symptoms reported.