Swapping your meat for two or more vegetables can reduce your blood pressure. An extensive study shows that a diet rich in vegetables, pulses and grains tends to produce lower blood pressure than one full of meat.

The findings could prove significant in the battle against the leading causes of death - strokes and cardiovascular disease. The research, led by Professor Paul Elliott of Imperial College, London, compared the diet and blood pressure of 4,680 men and women, aged 40 to 59, in four countries. Taking each volunteer's blood pressure eight times, and analysing detailed food diaries, the scientists found that those who ate more vegetable protein tended to have lower blood pressure than those who ate less.

Previous research has indicated that vegetarians are less likely to suffer from hypertension - abnormally high blood pressure - and high blood pressure than those who eat meat. But scientists had suggested this was due to vegetarians' lower body weight. The new research, published yesterday in the journal Archives of Internal Medicine, reveals it is the vegetable protein itself which is of benefit. "It is certainly true that vegetarians have lower blood pressure than meat eaters. What was unclear was whether this was due to their lifestyles or their vegetarianism," Prof Elliott, professor of epidemiology, said. "These people weren't vegetarians but people just eating their usual diets. But those consuming relatively more vegetable protein still had lower blood pressure than those who ate relatively more protein from meat."

Why vegetable protein affects blood pressure is not yet known, but the researchers suspect it may be due to amino acids. Some of these building blocks of protein have been shown to influence blood pressure, and different amounts were present in diets high in vegetable protein than in those that contained more animal protein. Magnesium, found in vegetables, may also interact with amino acids to lower blood pressure.

The study, conducted in Japan, China, Britain and America, chimes with recommendations that a diet rich in vegetables, low in salt, high in potassium and low in alcohol, helps high blood pressure and related chronic diseases. "We know high blood pressure is the biggest cause of preventable mortality worldwide," Prof Elliott added. "If we can stop the rise of blood pressure ... we will reduce the burden of stroke and heart disease."