What's the latest on Cholesterol and Heart Health?

This answer is brought to you by many of the Australian nutrition professionals who regularly contribute to a nutrition email discussion group.

Note that this FAQ addresses cholesterol and heart health for the general population. If you have a heart condition or are at increased risk of heart disease (e.g. because of elevated blood cholesterol or diabetes) always seek advice from your doctor or dietitian about your diet.

The following series of questions/answers concerns current knowledge about cholesterol and its effects on heart health. 

What exactly is 'cholesterol' and what are the differences between the 'good' and 'bad' forms of cholesterol we keep hearing about?

Cholesterol is a 'lipid' (that is, a fat-like substance) that is essential for animal life.

Cholesterol is an integral component of every cell in the human body and it has many and varied functions, including: 

• Production of vitamin D (which is formed from cholesterol just under the skin, using sunlight for energy);
• Absorption of fat (including the essential fatty acids) from our intestines; and
• Production of the steroid hormones, which include the sex hormones and other regulatory hormones such as cortisol (involved in response to stress and daily biorhythms) and aldosterone (involved in salt balance and blood pressure control). 

Although most of the cholesterol in our body is made in the liver, some is absorbed through the small intestine from dietary sources.

Cholesterol is transported in the blood from the liver and from the small intestine to the tissues where it is needed. The blood transports most of the cholesterol in a form known as ‘LDL’. LDL is commonly known as the 'bad' cholesterol (it is strongly associated with increased risk of heart disease).

Another cholesterol-containing substance in the blood (HDL) collects surplus cholesterol from the tissues and takes it away for disposal. Because it 'cleans up' excess cholesterol, HDL is often called the 'good' cholesterol (it helps protect against heart disease).

Although it is commonly called the bad cholesterol, LDL isn't actually intrinsically 'bad'. A certain amount of LDL must be present in our blood to provide the cholesterol needed by every cell in our body. The problem occurs when LDL in the blood increases above the optimal level. This can lead to the onset of 'atherosclerosis' (a build-up of cholesterol and other substances) inside the arteries, greatly increasing the risk of a heart attack or stroke.

What are the main factors that lead to increased LDL in the blood?

The two main factors that lead to high blood levels of LDL are genetic inheritance (that is, inheriting from your parents a tendency to high LDL) and eating a diet high in saturated fat. There isn’t much you can do about your genetics, but you can control the amount of saturated fat in your diet.

Important sources of saturated fat in the Australian diet include butter, cream, cheese and other full-fat dairy products and the fat associated with meat, especially in sausages, salami and other processed meats. Significant quantities of saturated fat are found in many baked goods (biscuits, cakes, pies, pastries), fried takeaway foods and snack foods (chocolate, potato crisps and extruded cheese flavoured foods). Finally, it should be noted that the ingredient listing vegetable oil on a food label does not necessarily indicate that the oil is low in saturated fat – it may be palm or coconut oil, two vegetable oils that also contain significant amounts of saturated fat.

Being overweight and being physically inactive are two other factors that contribute to elevated blood LDL levels and poor heart health. Cholesterol levels also tend to rise with age and are higher in men than women until menopause (after which, LDL levels in women start to catch up with those in men).

Trans fatty acids in food also raise LDL cholesterol. Pies, pastries, cakes and biscuits made with commercial shortening can contain trans fats. However, the level of trans fats in the Australian diet is estimated to be low – approximately one-twentieth of the amount of saturated fat (0.6% of total kilojoule intake).

What can I do to lower (or keep down) my blood LDL level?

Eating less saturated fat and partly replacing it with unsaturated fat will help to lower blood LDL or prevent its rise in the first place. To eat less saturated fat and tip the balance towards healthy unsaturated fats:

• Replace full-fat dairy foods with reduced-fat or low-fat varieties.
  Enjoy lean meats – trim visible fat from meat, remove the skin from chicken and limit sausages and processed meats.
  
  
• Replace butter with margarine spread (sunflower, canola or olive oil).
  
  
• Use mono- or polyunsaturated cooking oils (sunflower, canola, soybean or olive) instead of solid cooking fats (dripping, lard, copha, ghee).
  
  
• Limit intake of biscuits, cakes, pastries, fried savoury snack foods and fried fast food – snack on unsalted nuts instead. Replacing foods containing saturated fat with nuts has been shown to lower blood cholesterol by around 10%. (As discussed in greater detail in another FAQ in this series, eating a handful of nuts (~30 g) about five times a week has been shown to reduce the risk of heart disease by up to 50%).
  
  
• Choose products that specify the type of vegetable oil used on the food label.
  
  
• Avoid the food ingredient partially hydrogenated vegetable oil, which results in trans fats.
  
• Margarine spreads enriched with substances called 'plant sterols' have been shown to significantly lower LDL cholesterol. A number of other foods, such as yoghurt and milk, have now been enriched with plant sterols and would be expected to lower LDL as well.
  
  
• Maintaining (or regaining) optimal body weight and engaging in physical activity will have favourable effects on your blood LDL and on your general health and fitness too.
  
  
• Finally, drugs can now be prescribed by doctors to largely correct inherited high levels of LDL. Treatment will be most effective if it also includes appropriate diet, weight loss (if necessary) and physical activity. If you have been diagnosed as having an inherited tendency to high LDL, always take your doctor's or dietitian's advice on diet, weight loss and appropriate levels of physical activity.

What can I do to increase HDL – the good cholesterol?

HDL is decreased by being over-fat, physically inactive, smoking, eating large quantities of foods containing saturated fat, and by certain medications. HDL can therefore be increased by losing excess body fat, becoming more physically active, and reducing intake of saturated fat. Other factors that can assist include increasing intake of low GI carbohydrate foods and moderate alcohol intake.

I have heard that eating fish is good for the heart. Is this because of its effects on cholesterol?

Fish contain a type of fat known as 'omega 3'. The omega 3 fats are unsaturated fats that have been shown to reduce the risk of heart disease, although they seem to do this without significantly lowering LDL. Eating fish or other seafood once a week (or more) is associated with a significantly reduced risk of heart disease and other related diseases such as stroke.

What effect does eating more vegetables and fruits have on cholesterol and heart disease?

Although they do not significantly affect blood LDL levels, eating plenty of vegetables and fruits is thought to have a protective effect against heart disease. The antioxidants in vegetables and fruits may help protect LDL from oxidation and therefore make it less harmful to blood vessels. In Australia, the recommended daily intake is five serves of vegetables and two serves of fruit each day. 

Red wine and tea also contain significant quantities of antioxidants ( click here to see the FAQs on these subjects for more information), as does coffee. 

Does cholesterol in the food we eat increase our blood LDL?

It used to be thought that eating foods that are rich in cholesterol (e.g. eggs, offal, prawns and other crustaceans) would increase the levels of blood LDL. However, this is only true for a small proportion of people. For the majority, the body compensates for a large intake of cholesterol by absorbing less from the gut and by reducing production of cholesterol in the liver. In most people, eating four or five eggs a week (for example) is unlikely to be harmful to heart health. As noted above, the small proportion of the population with inherited conditions that cause high LDL levels should always take their doctor's or dietitian's advice on appropriate diet. 

What is the significance to health of the 'NO CHOLESTEROL' claim on some cooking oils?

As only animals contain cholesterol, the statement no cholesterol simply means that the oil was derived from a plant. However, as discussed earlier in this FAQ, such a claim does not inform you whether the oil is low in saturated fat, and this is most important for lowering cholesterol.

As noted above, some plant oils are quite high in saturated fats, particularly palm and coconut oils. Mono- and polyunsaturated fats (found in vegetable oils such as sunflower, canola, soybean and olive oils) are more 'heart-friendly' than saturated fats. Commercial frying oils rich in mono- and polyunsaturated fats are becoming more widely available in Australia, making fried food purchased away from home lower in saturated fat.

What about the claims that Metamucil reduces cholesterol levels; is this true?

Most, but not all studies have shown that soluble fibres such psyllium (found in Metamucil) and beta-glucan (from oats and barley) can reduce both total cholesterol and LDL cholesterol by 6 to 8%. The effect is small but significant, and can be another good addition to a healthy diet. Dietary sources of soluble fibre include apples, oat bran, barley, flaxseed (also known as linseed), dried beans (legumes), lentils, peas, soymilk and soy products.

Drugs and Cholesterol

Drugs can now be prescribed by doctors to largely correct inherited high levels of LDL or raise HDL levels. Treatment will be most effective if it also includes appropriate diet, weight loss (if necessary) and physical activity.

If you have been diagnosed as having an inherited tendency to high LDL or low HDL, always take your doctor's or dietitian's advice on diet, weight loss and appropriate levels of physical activity

For more information Nutrition Australia recommends:

• Eat Less Fat
• Weight for a Change
• Eating Activity Sport and You
  

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Disclaimer: This material is provided on the basis that it constitutes advice of a general nature only. It is not intended to replace the advice of a physician or a dietitian.