In a report on the findings, published in the British Journal of Nutrition, they said: "The changes we saw can be regarded as significant, considering that the time period was only three weeks and all the volunteers had normal cholesterol levels to start with."

Tomatoes have long been considered a health super-food.

Numerous studies have suggested that lycopene, the pigment that gives them their red colour, can protect against prostate cancer.

One study involving thousands of men found eating ten or more servings of tomatoes a week slashed their risk of prostate cancer by 45 per cent.

Lycopene is known to be a powerful antioxidant, helping to prevent damage to cells in the body.

Last year, Tesco launched the Healthy Living Tomato, one with twice the level of lycopene found in normal versions of the fruit.

Healthy levels of cholesterol are considered to be anything below 5 millimoles of fat per litre of blood. Around 70 per cent of people aged over 45 have high cholesterol.

Doctors are increasingly focusing on driving down 'bad' cholesterol and increasing levels of 'good' cholesterol, called high-density lipoprotein.

Researchers recruited 16 women and five men, all aged 20 to 49 and with normal cholesterol levels.

Each volunteer spent three weeks consuming no tomato products at all. Then they spent three weeks eating either 30g of ketchup a day or drinking 400ml of tomato juice.

During the experiment, researchers took regular blood samples to check cholesterol levels.

Total cholesterol went from a high of 4.5mmols per litre during the tomato-free period to 4.19 when they ate ketchup. LDL levels dropped from 2.56mmols per litre to 2.18mmols.