Fat is an important part of a healthy diet. However, some fats are better than others. Saturated fats increase blood cholesterol. Mono-unsaturated and polyunsaturated fats tend to lower blood cholesterol. Trans fatty acids (or trans fats) are potentially harmful and are used to make baked products, pies, cakes, biscuits and buns. Omega-6 and omega-3 fats can benefit your health.
Fat is important for many body processes. You need to eat some fat in your diet. Fat protects your organs, keeps you warm and helps your body absorb and move nutrients around. It also helps hormone production. However, some fats are better than others and having too much of any type is not a good idea.
Dietary fats are classified by their structure. Different types of fats react differently inside the body. Saturated fats (found mostly in animal products) increase blood cholesterol, which is a risk factor in coronary heart disease. Mono-unsaturated and polyunsaturated fats tend to lower blood cholesterol.
Dietary fats and blood cholesterol
The two types of blood cholesterol are low density lipoprotein (LDL) cholesterol and high density lipoprotein (HDL) cholesterol.
LDL is considered the ‘bad’ cholesterol because it contributes to the narrowing of the arteries, which can lead to heart disease and stroke. HDL cholesterol is considered to be the ‘good’ cholesterol because it actually carries cholesterol from the blood back to the liver, where it is broken down, reducing the risk of cardiovascular disease.
Groups of fats
Each group of fats behaves differently inside the body. Dietary fat can be classified into four groups. These are:
- trans fats.
Saturated, mono-unsaturated and polyunsaturated fats
Saturated fats contribute to the risk of heart disease by raising blood cholesterol levels. These fats are commonly found in many takeaway (‘fast’) foods, in commercial products such as biscuits and pastries, and in dairy products.
Mono-unsaturated and polyunsaturated fats both tend to lower blood cholesterol when they replace saturated fats in the diet. Polyunsaturated fats have a slightly greater impact than mono-unsaturated fats.
Replace saturated fats in your diet with either mono-unsaturated or polyunsaturated fats whenever possible. For example, replace butter in some cooked dishes with olive oil or margarine.
Trans fatty acids
Trans fatty acids are rare in nature. They are only created in the rumen of cows and sheep, and are naturally found in small amounts in milk, cheese, beef and lamb. Trans fatty acids are also created during the manufacture of some table margarines and in solid spreads used in the food industry to make baked products such as pies, pastries, cakes, biscuits and buns.
Trans fatty acids tend to behave like saturated fats in the body, as they raise LDL levels and increase the risk of heart disease. Unlike saturated fats, they tend to lower HDL cholesterol, so are potentially even more damaging.
It is the trans fats that are produced during food manufacturing that you should be most concerned about, not the trans fats present naturally in certain foods. Look for margarines that have less than one per cent trans fats on the label or choose foods with the Heart Foundation Tick. Limit how much takeaway food and packaged snack foods you eat.
Common fat-containing foods
Different foods contain different ratios of fatty acids. For example:
- Saturated fats – sources include fatty cuts of meat, full-fat milk, cheese, butter, cream, most commercially baked products such as biscuits and pastries, most deep-fried fast foods, coconut and palm oil.
- Mono-unsaturated fats – sources include margarine spreads such as canola or olive oil based choices, oils such as olive, canola and peanut oils, avocado, and nuts such as peanuts, hazelnuts, cashews and almonds.
- Polyunsaturated fats – sources include fish, seafood, polyunsaturated margarines, vegetable oils such as safflower, sunflower, corn or soy oils, nuts such as walnuts and Brazil nuts, and seeds.
Sources of omega-6 and omega-3 fats
Polyunsaturated fats can be divided into two categories, which are:
- Omega-3 fats are found in both plant and marine foods, although it is the omega-3 fats from marine sources that have the strongest evidence for health benefits (including reducing the risk of heart disease). Plant food sources include canola and soy oils, and canola-based margarines. Marine sources include fish, especially oily fish such as Atlantic salmon, mackerel, Southern blue fin tuna, trevally and sardines.
- Omega-6 fats are found primarily in nuts, seeds and plant oils, such as corn, soy and safflower.
Benefits of omega-3 fats
Research is ongoing, but the benefits of omega-3 fats in the diet seem to include that they:
- lower triglyceride levels, which are important risk factors in coronary heart disease
- improve blood vessel elasticity
- keep the heart rhythm beating normally
- thin the blood, which makes it less sticky and less likely to clot
- reduce inflammation and support the immune system
- reduce blood pressure
- may play a role in preventing and treating depression
- contribute to the normal development of the fetal brain.
Plant sterols are present in all plants. Intakes of 2–3 g of plant sterols per day have been shown to reduce blood cholesterol levels by an average of 10 per cent. This is because they block the body’s ability to absorb cholesterol, which leads to a reduced level of cholesterol in the blood.
However, it is hard to eat this amount of plant sterols from natural sources, so there are now plant sterol-enriched margarines and dairy products on the market. Eating 1–1.5 tablespoons of sterol-enriched margarine each day can help to lower blood cholesterol levels.
Energy density of dietary fat
Dietary fat has more than double the amount of kilojoules per gram (37 kJ/g) than carbohydrate or protein (17 kJ/g), making it very ‘energy dense’. Foods high in fat are usually high in kilojoules. Some research suggests that saturated fats are more likely to contribute to weight gain (especially around the waistline) than polyunsaturated fat and mono-unsaturated fats, even though they have the same kilojoule content.
Carrying too much body fat is a risk factor in many diseases, including coronary heart disease, type 2 diabetes and many cancers.
Cholesterol in food
People with high blood cholesterol or who are at risk of heart disease should also try to limit their intake of cholesterol-rich foods. However, while cholesterol in food can raise blood cholesterol levels, the effect is small compared to the effects of saturated fat.
Dietary cholesterol is only found in animal products such as:
- full-fat dairy products
- fatty meats
- egg yolks
- offal – for example, liver, kidney and brains.
The Mediterranean diet
Researchers are investigating the possibility that a diet rich in mono-unsaturated fats, such as olive oil, may be protective against the development of coronary heart disease. People who have a high consumption of mono-unsaturated fats from olive oil (for example, in Greece and Italy) tend to have low rates of coronary heart disease, regardless of their body weight.
Studies have shown that olive oil consumption may have a protective role on breast, colon, lung, ovarian and skin cancer development. Compounds specific to olive oil, known as phenolics, seem to possess free radical-scavenging properties and so may be able to reduce oxidative damage to DNA.
A number of studies have also shown that olive oil may have additional beneficial effects on blood pressure, obesity, rheumatoid arthritis and immune function.
We must remember, though, that the Mediterranean diet contains much more than olive oil. It’s possible that the low rate of coronary heart disease in these countries relates to a high intake of vegetables, legumes, fruits and cereals, which are rich in antioxidants.
Current recommendations on fats in your diet
Nutritionists recommend that we limit the amount of fats in the daily diet, particularly saturated and trans fats. Simple suggestions include:
- Use margarine spreads instead of butter or dairy blends.
- Use salad dressings and mayonnaise made from oils such as canola, sunflower, soy and olive oils.
- Use low or reduced-fat milk and yoghurt or ‘added calcium’ soy drinks.
- Try to limit cheese to twice a week.
- Have fish (fresh or canned) at least twice a week – limit fish that is high in mercury to once a week. Very young children and women who are pregnant (or intending to become pregnant within the next six months) are advised to eat fish that is low in mercury (shellfish, salmon and canned tuna).
- Select lean meat (meat trimmed of fat and chicken without skin). Try to limit fatty meats, including sausages and delicatessen meats such as salami.
- Snack on plain, unsalted nuts and fresh fruit.
- Incorporate dried peas (for example, split peas), beans (for example, haricot beans, kidney beans, three bean mix) or lentils into two meals a week.
- Make vegetables and grain-based foods, such as breakfast cereals, bread, pasta, noodles and rice, the major part of each meal.
- Try to limit takeaway to once a week or less.
- Try to limit snack foods such as potato crisps and corn crisps to once a week or less.
- Try to limit cakes, pastries and chocolate or creamy biscuits to once a week or less.
- People with high cholesterol should try to limit cholesterol-rich foods such as egg yolks, and offal like liver, kidney and brains.
Where to get help
- Your doctor
- Dietitians Association of Australia Tel. 1800 812 942
Things to remember
- Dietary fat contains more than double the amount of kilojoules per gram than carbohydrate or protein.
- Animal products and some processed foods, especially fried fast food, are generally high in saturated fats, which have been linked to increased blood cholesterol levels.
- Replacing saturated fats with mono-unsaturated and polyunsaturated fats tends to improve blood cholesterol levels.
You might also be interested in:
- Cancer and food.
- Food to have sometimes.
- Healthy eating for kids.
- Healthy eating tips.
- Kilojoules and calories.
- Liver - fatty liver disease.
- Olive oil.
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Deakin University - Faculty of Health and Behavioural Sciences
Last reviewed: July 2013
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