Scientists measured blood pressure, artery health and heart disease risk factors such as high cholesterol in 162 non-smoking men and women aged 40 to 70.

One group ate a diet high in saturated fat, salt and sugar, and low in fibre, oily fish and fruit and vegetables. The other consumed a diet with higher amounts of fruit and vegetables and lower levels of animal fat, that included oily fish once a week, replaced refined with wholegrain cereals, and restricted sugar and salt intake.

Men and women in the “healthy diet” group were also asked to replace cakes and biscuits with fruit and nuts and were also supplied with cooking oils and spreads high in mono-unsaturated fats.

The healthy diet, based on UK guidelines, was associated with significant falls in blood pressure, an average reduction in heart rate of 1.8 beats per minute, and an 8% fall in cholesterol levels.

Overall, the study, published in the American Journal of Clinical Nutrition, found that men and women over the age of 40 who adapted their diet reduced their risk of heart disease by up to a third.

Prof Tom Sanders, from King’s College London, said: “Our findings apply to middle-aged and older people without existing health problems. This is important because most heart attacks and strokes occur in those not identified as being at high risk.

“We show that adherence to current dietary guidelines which advocate a change in dietary pattern from the traditional British diet (high in saturated fat, salt and sugar, low in fibre, oily fish and fruit and vegetables) would substantially lower that risk.”

Average body weight within the group following the modified diet fell by 1.3kg (2.8lbs) while that of “traditional” diet participants rose by 0.6kg (1.3lbs) after 12 weeks.

Waist circumference was 1.7cm (0.6in) lower in the modified group compared with the traditional group.

Dr Alison Tedstone, chief nutritionist at Public Health England, said: “PHE has always recommended a balanced diet that is low in saturated fat, salt and sugar and includes oily fish and five portions of fruit and vegetables a day as part of a healthy lifestyle that includes keeping active and not smoking. This study clearly illustrates that following this advice will protect your health by significantly reducing your risk of heart disease.”

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