Last updated by Dr Sarah Brewer on
If you have a raised cholesterol and a high blood pressure, you may have spotted recent headlines suggesting the so-called Portfolio diet was more effective than the Dietary Approach to Stopping Hypertension (DASH) diet for lowering BP. This may sound like good news, but the difference between the two approaches was small. In fact, those following the portfolio diet for 24 weeks only reduced their blood pressure by a mere 2.5/2mm mmHg, while those following what was termed a DASH style diet improved their blood pressure by just 0.4/0.2mmHg – a result which falls within the limits of recording error. These unstunning results did not seem to warrant the headlines promoting the portfolio, and left me questioning whether the DASH diet was followed correctly.
What did the researchers do?
The researchers asked 241 Canadians with raised cholesterol to either follow the portfolio diet or a DASH-style diet for 24 weeks. Those on the portfolio diet were asked to eat guideline amounts of foods that are known to lower cholesterol; for every 1000 kcals daily energy intake, they were to eat 22.5g mixed nuts, 22.5g soy protein (from soy milk, tofu and soy meat substitutes), 0.94g plant sterols (from fortified margarine enriched with plant sterols) plus 9.8g soluble fibre (from oats, barley, psyllium, aubergines/eggplant and okra).
Those following the control diet, based on the DASH approach, were asked to eat a low-saturated fat, lacto-ovo-vegetarian diet that focused on fruits, vegetables, low-fat dairy and whole grain cereals with a reduction in red meat and snack foods.
It seems that the portfolio diet wasn’t that popular, as adherence to the desired number of servings was just 48% – less than half that achieved by those following the DASH style approach. No differences were seen in body weight, BMI or waist circumference between the two groups, over the 24 weeks, and there were no changes in the number of people taking blood pressure medications or the doses used.
Results Were Unimpressive
Overall, the improvement in blood pressure favouring the portfolio over the DASH approach was just 2.6/1.5mmHg. The corresponding reductions in relative risk of having a heart attack or stroke over the next ten years were a mere 1.2% to 1.4%, which hardly seems worth the effort. So what went wrong?
The main problem with the study was that those taking part already had an impressively low blood pressure averaging 119/73 mmHg at the start – they were mostly already on antihypertensive medication and obviously responding so well that achieving further reductions from dietary changes was always going to be difficult without a few swoons.
Another problem was that the study didn’t seem to emphasise a lower salt intake. Were participants advised to eat unsalted mixed nuts rather than salted nuts for example? The published paper does not make this clear. What it does say is that there were no changes in dietary sodium intake between the two groups, and that sodium intakes remained constant – so no attempt was made to lower intakes. One of the main features of the original DASH diet was that it was low sodium, so don’t let these recent headlines put you off. The DASH diet is effective if you follow it properly.
To find out how to follow the DASH diet and other ways to help lower your blood pressure, visit mylowerbloodpressure.com.
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