Cholesterol and dietary fat: confusing isn't it?

Did you know that every cell in your body is surrounded by a membrane containing fat? These membranes need a regular supply of dietary fats to remain flexible, so when you eat a low fat diet you are not supplying the raw materials your body needs to renew these membranes, meaning they can become rigid. When this happens it is difficult for nutrients to get into cells and waste to get out. This includes fat cells. We've all been conditioned to think that fat is bad and low fat is good, particularly for weight loss, but it's not the case. A balanced diet needs to contain adequate levels of healthy fats.

What about cholesterol though? For a long time saturated fat has been associated with high cholesterol, and high cholesterol an increased risk of cardiovascular disease. If a blood test reveals an increase in serum cholesterol levels it has been reason for concern, and on the back of that we have been taught to avoid saturated fat and eat low fat foods instead. However, more recently it has been suggested that saturated fat and high cholesterol levels per se are not to blame for increased cardiovascular disease risk.    

Cholesterol is actually vital to our health. Hormones, such as testosterone, oestrogen and cortisol use cholesterol as a building block; cell membranes need it to remain flexible and let nutrients in and waste out; it is part of the structure of bile acids, which are required for digestion and absorption of dietary fat; and it is needed for the body to absorb fat soluble vitamins (A, D and E). Bile is also needed to excrete excess cholesterol from the body, so you need high enough levels of cholesterol for your body’s own built-in mechanism to regulate cholesterol levels.    

In a healthy body the liver produces most of the cholesterol you need, and only a small amount is absorbed from dietary intake. If dietary intake is particularly high your liver should adjust how much it's producing so that levels remain healthy. If you are particularly stressed, or the liver is in some way compromised however, this can affect cholesterol levels in the body. So supporting liver health is fundamental to your body being able to keep cholesterol levels where they need to be.

That doesn’t mean you shouldn’t be discerning about the types of fat you eat: some have no place in a healthy diet. Hydrogenated/partially-hydrogenated/trans fats are vegetable oils which have had hydrogen artificially added to them. This causes them to turn solid at room temperature. The beauty of them (for the food manufacturer, not our bodies!) is that they extend shelf-life in processed foods. If you like buying baked goods with a long sell-by date then be aware that it is highly likely that they contain these fats which have a detrimental effect on the body (they have been linked to increased incidence of heart disease and inflammation for example[i]). Another one to be aware of is how cooking with vegetable oil changes its properties. Saturated fat (e.g. coconut oil) is very stable at high temperatures, whereas something like sunflower oil becomes oxidised when you heat it (oxidised means free radical damage is likely). So the message that saturated fat is bad is not at all clear cut.

The mixed messages about cholesterol and dietary fat can make deciding whether saturated fat and cholesterol have a place in a healthy diet difficult. If you have been diagnosed with high cholesterol and want some advice on how you can help yourself with dietary choices a nutritional therapist will be able to give you that help.

[i] Mozaffarian D, Aro A, Willett WC (2009). Health effects of trans-fatty acids: experimental and observational evidence. Eur J Clin Nutr 63(Suppl 2), S5–S21.

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