All are difficult habits to kick. For some, the changes needed are only small, like getting in some exercise on the way home by getting off the train a stop early and walking the rest of the way.

But for others, the problems are harder to tackle.

Hardened smokers may need the support of not only their families, but their friends, colleagues and even doctors to wean themselves off nicotine.

Many view changing over to a healthy diet as a major feat. They think they will have to resign themselves to a life of vegetables and chocolate and chip abstinence.

Nutritionists agree it can be difficult to change the habits of a lifetime, but they say drastic alterations may not be required.

Switching from full fat to semi-skimmed milk, for example, can have major health benefits with little taste difference.

And there is no need to forswear "naughty but nice" food for ever - as long as it does not form a staple part of your diet.

The British Nutrition Foundation says there are five main areas of diet which can prevent coronary heart disease.

Cholesterol

Cholesterol is a form of fat transported in the blood which is essential in small amounts.

Some forms of cholesterol - those derived from saturated fats - can clog up the arteries in large amounts.

This increases the risk of the blood supply to the heart being cut off, resulting in a heart attack.

These types of cholesterol are found in products like margarine, butter, lard, meat, milk, yoghourt, cheese, cakes, biscuits, pies and chips.

The build-up of damaging levels of cholesterol can be counteracted by chemicals called antioxidants.

Vitamin C, vitamin E and some forms of vitamin A contain antioxidants.

Fruit and vegetables are good sources of vitamins A and C and unsaturated fats and oils are good sources of vitamin E.

The British Heart Foundation recommends that people eat five portions of fruit and vegetables a day to keep their hearts healthy.

Blood pressure

High blood pressure is a risk factor for coronary heart disease.

Burgers are high in cholesterol

It can be caused by genetic conditions, but diet is also thought to play a big part.

People who are overweight, drink a lot of alcohol, smoke, take little exercise and eat a lot of salt are particularly likely to have high blood pressure.

Cutting down salt levels can be difficult because many foods and drinks contain it.

Bread is the single largest source of dietary salt. Processed food, such as prepared meals, are also high in salt.

The British Heart Foundation advises against adding any extra salt to food since most already contains fairly high quantities.

A recent study in The Lancet showed that many people could not tell the difference between high and low salt foods.

The food manufacturers' argument against lowering salt content in food has always been that people like the taste.

Other studies suggest that foods which are high in minerals like potassium, such as bananas and potatoes, may also play a role in lowering blood pressure.

Maintaining a healthy weight

People who are obese run an increased risk of heart disease.

Too much fried food increases fat intake

Heart experts say physical activity can reduce the risk of high blood pressure caused by constricted arteries.

The way the fat is deposited around the body can also affect the risk.

People with pear-shaped figures - people with most of their fat deposited around the hips - run less of a risk of suffering a heart attack than those with apple-shaped figures who have most of the fat deposited around their stomach.

Men are more likely to be apple-shaped than women.

Blood clots

Blood clots can block or stem the blood flow, causing a heart attack.

So foods which contain chemicals which prevent blood clotting can protect against heart disease.

These include naturally oily fish, such as mackerel, sardines and salmon.

Fibre

Fibre has been shown to reduce blood cholesterol levels and may therefore reduce the risk of heart disease.