High blood pressure is a major risk factor for heart disease and strokes. A healthy diet is an important part in the prevention and management of high blood pressure. Clinical trials show that eating plenty of whole grains, fruits, vegetables, lean meats, nuts and seeds and cutting back on foods high in saturated fat and salt can lower blood pressure.
Nuts are a feature of heart-healthy diets the world over and researchers have looked at one specific type of nut – walnuts – to see if having more of these could help improve blood pressure.
Walnuts are a rich source of the polyunsaturated omega-3 fatty acid called alpha-linolenic acid (ALA) along with a range of beneficial plant compounds that are present in higher amounts than other types of tree nuts.
Observational research links diets high in ALA to lower blood pressure, so this raises the question of whether including more walnuts in the diet could be a useful strategy to help control blood pressure.
In the latest research, a group of 45 overweight volunteers who were at risk of cardiovascular disease were recruited for the diet trial. For the first two weeks, the participants followed a typical American diet where 12 per cent of their kilojoules came from saturated fat.
After the lead-in diet was finished, each person was randomly allocated to one of three diets, all of which were low in saturated fat.
The diets either included whole walnuts (57 to 99 grams per day), the same amount of ALA found in walnuts but with no walnuts eaten, or a diet that had a similar amount of the mono-unsaturated fatty acid oleic acid (found in olive oil) to the ALA levels found in walnuts.
Each diet was followed for six weeks with the number of kilojoules on each diet designed to keep body weight stable.
At the end of the trial, people who were eating walnuts daily showed the greatest benefit on lowering central blood pressure. Central blood pressure is a measure of the pressure exerted on internal organs like the heart and is considered an important risk factor for cardiovascular disease.
All three study diets improved blood lipids such as total cholesterol and LDL-cholesterol to a similar extent.
The greater blood pressure benefit from eating walnuts shows that it is likely not just because of their ALA content. Walnuts contain a range of bioactive phenolic compounds in addition to fibre that could play a part in lowering blood pressure so this study again points to the benefits of eating whole foods rather than focussing on individual nutrients.
Eating walnuts as part of a heart-healthy diet lower in saturated fat may make for a great snack idea that is good for blood pressure, heart and brain.