I have a friend who had high cholesterol and was told to lower it by diet. The GP said to choose foods with little or no saturated fat. No mention was made of carbohydrate intake (including sugar), or the importance of eating healthy fats, like oily fish. She stuck to a low-fat diet rigidly for 6 months. On returning for a follow-up blood test, her cholesterol levels had increased.

It's a common myth that the answer to high cholesterol^[1] is a low-fat or zero-fat diet. As a result, we've come to equate the word 'cholesterol' with something negative and heart-damaging, an enemy to good health. Our fat intake is held to solely to blame.

Actually, cholesterol is an essential part of our body chemistry.

Cholesterol isn't the big bad wolf then. It's just doing its job.

So why, then, do we talk so much about cholesterol in relation to cardiovascular disease?

• Studies (dating back to the 1960s)^[2] showed a link between fat intake, cholesterol levels, and cardiovascular disease - although since then other studies have questioned that link and looked at other dietary risks^[3]
• Cholesterol is one of the substances that creates atherosclerosis (plaque in blood vessels) as pictured below - but it's actually oxidised low-density lipoprotein cholesterol that's the biggest problem^[4]

Before we get started on what really is the issue with fat and cholesterol, let's just be clear that arteries can become blocked and cause strokes or heart attacks. It's a known fact, one that became frighteningly real to me when my husband had a heart attack when he was 47 (he's fine now). However, saying that all fats in the diet cause high cholesterol is unscientific.

Conversely, it's also important not to deceive ourselves. Many fans of ketogenic diets like to minimise the risk of high fat intake on heart disease, but they are flying in the face of evidence. There is evidence that fat intake is associated with cardiovascular disease, but it's not the only cause.

Cardiovascular disease is the biggest killer in the developed world and our diet is one of the primary contributing factors. Generally, in the Western world, we consume lots of processed food, refined grains (white bread and pasta), and sugar. We don't consume a lot of fruit and vegetables or high fibre foods.

We also eat a lot of fat without paying attention to type: from processed trans fats in foods like pre-made chicken pie or margarine; to saturated fat in meat and cheese; to high quantities of monounsaturated or polyunsaturated fats in the vegetable oils we cook in^[5].

This combination of lots of processed foods, low fibre, high fat intake (the wrong types of fat), and high sugar is causing inflammation throughout our body and creating a metabolic nightmare, also increasing the likelihood of obesity and type 2 diabetes. This combination of high inflammation and high circulating fats are big risks when it comes to cardiovascular disease.

So how should we eat for good heart health?

A low-fat diet isn't the answer, as that doesn't address the whole issue. Low-fat products are often higher in sugar, which increases our risk. If we eat lots of starchy foods and sugary products, the excess glucose in our bloodstream actually gets converted into a type of fat that is stored around our middle. These fats (triglycerides) are really susceptible to oxidative damage and increase our risk of cardiovascular issues.

This is how to eat for a healthy heart. Focus on the following:

Healthy Fats: The healthy fats in our diet should come from oily fish (mackerel, sardines, salmon, trout), as the Omega 3 from this oil is anti-inflammatory and really good for our heart health.

Saturated fat can also be tolerated in sensible quantities (as a rough guide, if you have high cholesterol avoid going above 15g per day). There are nutrients we need that are found in animal products that contain saturated fat, such as Vitamin B12, Vitamin D, and Zinc. So stick to lean meat, and if you're vegetarian, stick to soft cheeses like feta or cottage cheese, and don't have more than 30g per portion.

Healthy fats also include nuts and seeds, which despite containing quite high levels of fat, have been shown to reduce the risk of heart disease^[6]. For cooking, use olive oil for cooking temperatures up to 230 degrees centigrade, and coconut oil for anything beyond.

High fibre: High fibre foods include wholegrains, fruit, vegetables, beans & pulses. Particularly helpful examples are apples, avocadoes, beetroot, blueberries, and brown rice (which contains gamma-oryzanol linked to lowering LDL cholesterol).

It's also good to include whole oats, as they contain beta glucans, which help to remove excess cholesterol through the bowel before it's reabsorbed into our circulation. Apples are good for this too as they contain pectin which plays a similar role.

Flavonoids: Flavonoids are what give food colour - think gorgeous purple berries or bright red peppers. Flavonoids are phytochemicals which can interact with our cells in our blood vessel wall, causing them to release nitric oxide, relaxing the muscle and helping reduce our blood pressure.

Choosing the right things to eat is halfway there - now you also need to avoid these foods:

Avoiding the unhealthy foods doesn't mean you have to eat carrot sticks at parties or never have dessert again. Eating well isn't about perfection - if you can follow the above 80% of the time then you'll be doing a lot to help your body avoid strokes and heart attacks.

So what have we learned?

• Cholesterol is a carrier of fatty lipids and an essential part of our body chemistry

• We need some fat in our diet, especially sources of Omega 3

• Blood sugar management is vital for heart health, bad management increases triglycerides

• Good fibre intake helps excess fat to leave our body rather than re-enter circulation

• Our whole diet contributes to our cardiovascular health - low sugar, high fibre, and a balanced amount of healthy fat

My aforementioned friend put the above into practice with gusto - she reduced her sugar intake, increased fibre, reduced processed foods, and had a balanced intake of fat. Her last cholesterol blood test was a smug 4.4.

NB: If you'd like to understand the process of how atherosclerosis develops, here's a step-by-step of how blood vessels can become blocked:

1. It starts with the wall of our vessels getting damaged. This can be caused by high blood pressure, but other factors including smoking, infection, even inactivity.

2. This damaged area then becomes inflamed, as our immune system sends cells to repair the damage

3. Circulating material in our blood (fats and cholesterol) then get embedded in the inflamed area in our vessel wall

4. Embedded cholesterol is more susceptible to oxidation, so that triggers another inflammatory response

5. White blood cells move up to the injury, swallow the oxidised cholesterol, and become foam cells

6. Foam cells cannot circulate, so they are stuck at the site of injury. Cells in the vessel wall swallow up the foam cells and form a 'cap'. This can be stable (i.e. it stays in place) or unstable, in which case high blood pressure or inflammation can dislodge it.

7. A blood clot now forms around the site, a bit like a scab when you scrape your skin. This clot contains platelets and fibrin and can grow large, large enough to block a blood vessel. Whatever tissue that blood vessel fed oxygen to is now starved and may lose function or die completely. If a vessel leading to the brain gets blocked, the person will have a stroke; if it is in a vessel leading to the heart, the person will have a heart attack.