Early results of the trial have shown that their near monastic lifestyle turned out to be better for their friends as well, the patients becoming less hostile and aggressive.
Dr Larry Scherwitz, of the San Francisco Heart Trial, said in Barcelona yesterday that he believed diet was the most significant factor in their improved health.
'If I had to choose any one thing I would go for a low-fat vegetarian diet. Twenty per cent fat in the diet is a lot better than 30 per cent but not as good as 10 per cent. You should get as low as possible on fat if you want to leech those lipids (fats) out of the arteries.' .
Dr Scherwitz said that the study, due to end in three months' time, proved that it was possible to reduce the risk of serious heart problems without the use of drugs while living a normal life at home.
Forty-eight middle-aged men and women suffering from disease of the arteries had been taking part in the four-year programme. The state of their blood vessels was measured by diagnostic screening techniques at the start of the trial, after one year and at its conclusion.
The participants' vegetarian diet was made up of 10 per cent fat, 25 per cent protein and 75 per cent complex carbohydrate - bread, pasta and rice. They were only allowed one small measure of alcohol a day; they did not smoke. During an initial week in a hotel, they were taught stress management techniques including relaxation which they practised for one hour a day.
Their exercise was a walk of 30 minutes, three times a week, and once a week they met and received support and counselling.
On average the patients lost 22lb in weight (10kg) in the first year and on psychological scores were found to be less aggressive and less hostile than previously.
Results showed a dramatic reduction in blood cholesterol levels and a reduction in the amount of chest pain, Dr Scherwitz said.
Arteries that had been 57 per cent blocked improved by 15 per cent and a scan of one man at the end of his four-year trial showed that the blood supply to his heart muscle had significantly improved.
'The more lifestyle changes you make, the more regression you will see in atherosclerosis (thickening of arteries),' Dr Scherwitz said.
Gerry Saper, Professor of Epidemiology at the Royal Free Hospital Medical School, London, said the message to the public was that regular exercise was a good way to protect against heart disease.
'Moderate activity should be sufficient to provide a significant reduction in heart attacks,' he said. He defined moderate activity as some form of sport at least once a week, plus other activities such as gardening or DIY.
Dr Anthony Keech, of the Oxford University study into cholesterol-lowering drugs, said that the public were confused over advice on how best to lower their blood-fat levels.
Doctors were still arguing over the safety of drugs and over recent findings that suddenly lowering blood cholesterol may make people more at risk of suicide and violent death.