A recent Viewpoint in JAMA focused on the 20 year anniversary of the DASH diet, one of the major breakthroughs in blood pressure control:
This year marks the 20th anniversary of the publication showing the blood pressure–lowering effects of the Dietary Approaches to Stop Hypertension (DASH) diet. The DASH diet is considered an important advance in nutritional science. It emphasizes foods rich in protein, fiber, potassium, magnesium, and calcium, such as fruits and vegetables, beans, nuts, whole grains, and low-fat dairy. It also limits foods high in saturated fat and sugar. DASH is not a reduced-sodium diet, but its effect is enhanced by also lowering sodium intake. Since the creation of DASH 20 years ago, numerous trials have demonstrated that it consistently lowers blood pressure across a diverse range of patients with hypertension and prehypertension.
Everything in this paragraph is factually correct. The original DASH study was a multi-site randomized controlled trial. It showed that those who stuck to the diet had a significant reduction in their blood pressure compared to those who ate a normal American diet (5.5 systolic reduction and 3.0 diastolic reduction). There have been many trials that have confirmed that, for those who have high blood pressure, the DASH diet can work to lower it.
Unfortunately, that's not how the Viewpoint judges success, though. It notes that adherence to the DASH diet on a national level is really low; fewer than 1% of people in the United States overall conform to the DASH diet. But the benefits of the DASH diet are not necessarily confirmed in the national population. They're robust in the population that has been studied extensively - those with high blood pressure.
It would seem that the goal should be for those who meet that criterion to be on the DASH diet. Asking for more means wasting resources on interventions for which there is limited evidence.
Too often, though, this is how we handle nutritional interventions with respect to disease. We show that they can lead to small improvements in specific populations (ie those with metabolic syndrome, those at high risk for cardiovascular events, or even those at high risk for cancer). Then, we demand that everyone start to follow those recommendations, even those without those risk factor or those without specific conditions. This not only dilutes the effect; it spreads resources thinner.
Moreover, while the DASH diet did not focus on sodium reduction specifically, that's what most organizations seem to focus on. The FDA still recommends we consume less than 2.3 grams of sodium a day, the WHO says less than 2 grams, and the AHA says less than 1.5 grams. Never mind that diets with that little sodium are not well supported by evidence, and may actually lead to harm.
Laws are being passed in some areas that don't advocate for improved diets along the lines of DASH. They advocate to limit sodium directly, only in very high sodium products, and only in certain locations. Again, focusing on these targets may not achieve the goals we want.
At the end of the Viewpoint article, the authors note once again that if people with hypertension were fully adherent to a DASH diet, we could prevent about 400,000 cardiovascular events over a decade. Unfortunately, we don't seem committed to policy changes that focus on diet, nor to focusing on the populations most at risk. Our actions don't line up with the evidence. If we want to see research implemented well in the real world with effects we can see, we need to focus on making policy consistent with the studies we do, focusing on the populations where the benefits will likely be seen.