Fat facts

We all love the flavour that oil brings to food. Gram for gram, however, fat contributes more kilojoules than carbohydrates or protein. All oil is 100 percent fat; cutting back can help you stay in shape.

But for the health of your heart and arteries, it’s the type of fat that matters (see “What is cholesterol?”, below).

Fats and oils are made up of fatty acids – saturated, trans, monounsaturated and polyunsaturated. All fats are made up of a mixture of these fatty acids, with one type usually predominating in each oil or fat.

Types of fat

Saturated fat
Saturated fat raises the total amount of cholesterol – and the amount of “bad” low-density lipid (LDL) cholesterol – in your blood. Saturated fats can also promote blood clotting, which can lead to a heart attack or stroke. Certain cancers (breast and bowel cancer) have been linked with high intakes of saturated fat.

Tip: Fats high in saturates are usually solid at room temperature. You’ll find saturated fat in meat, full-fat dairy products, butter, spreads, cakes and biscuits. Palm and coconut oil are high in saturated fat too.

Trans fat
This  has the same effect as saturated fat because it raises both total and LDL cholesterol. Trans fat also decreases “good” high-density lipid (HDL) cholesterol levels.

Small amounts of certain trans fats occur naturally in butter, milk, cheese and meat. But the problematic trans fats are mostly formed when liquid oils are hydrogenated. This is the process of adding hydrogen, which hardens fats and makes them more stable and convenient to use.

Tip: You’ll find trans fats in some table spreads, cakes, biscuits and other processed foods. Liquid vegetable oils have negligible amounts of trans fats.

Monounsaturated fats
These are “good” fats. They lower total and LDL cholesterol and appear to have little adverse effect on HDL cholesterol. Avocado, canola, macadamia nut and olive oil are good sources of monounsaturates.

Polyunsaturated fats
These are also “good” fats that have been found to lower total and LDL cholesterol. High intakes may lower HDL cholesterol. Sunflower, safflower, soya bean and grapeseed oils are good sources of polyunsaturates.

Omega fatty acids
Omega fatty acids are polyunsaturates that are essential for health – our body can’t make them so we need them in our diet. Omega-6 fatty acids are more prevalent in the oils of seeds and grains, like sunflower and corn oil. Flaxseed and fish oils are good sources of omega-3 fatty acids. The omega-3s found in fish oils are beneficial for many conditions including heart disease, joint mobility, and brain and eye development.

What is cholesterol?

Cholesterol is a fatty substance that is essential to help build the hormones and nerve cells your body needs. But too much cholesterol may thicken the walls of your blood vessels, increasing your risk of heart disease and stroke.

Cholesterol mainly gets around in the blood attached to LDLs and HDLs as carriers.

LDLs are the “bad” form. If you have high levels of them in your blood, it’s likely some will be deposited as fatty streaks on your artery walls – which increases your risk of heart disease. In contrast, HDLs help slow this process by carrying cholesterol out of the tissues and back to the liver for processing.

The liver makes most of the cholesterol your body needs. We also get cholesterol from eating animal products such as meat, eggs and dairy products.

However, LDL-cholesterol levels are linked more strongly to your intake of saturated and trans fats than to your intake of cholesterol-containing foods. So watch out for “low” or “no” cholesterol foods that are high in saturated or trans fats. 

Monos or polys?

Health experts advise replacing saturated and trans fats with monounsaturated and polyunsaturated fats. But which is better: mono or poly?

There’s no definitive answer. They both lower total and LDL cholesterol. But some studies suggest that very high levels of polyunsaturated fats can, in addition to lowering the LDL cholesterol, also lower the “good” HDL cholesterol. It’s unlikely you’d eat such high levels in a normal diet.

Polyunsaturated fats appear to be more susceptible to oxidation than monounsaturates. There’s concern that oxidised oils may have bad health effects.

On the other hand … the omega-3 polyunsaturates found in fish oils appear to decrease blood clotting, which can reduce your risk of heart disease. Monounsaturates don’t have this effect.

Tip: The best advice is to replace some of the saturated fat with a mix of monounsaturated and polyunsaturated fats, and to focus on monounsaturates and omega-3s. Many vegetable oils are low in saturated fats and either high in monounsaturated or polyunsaturated fat.