Dietary Fats Explained: Saturated Fat, Seed Oils, Omega-3s and Your Cholesterol

The Main Types of Dietary Fat

All dietary fats are high in energy, but their effects on health differ depending on their chemical structure. There are four broad categories worth understanding.

Saturated fats are found mainly in animal products, fatty meat, butter, cream, full-fat dairy, and in a few plant sources like coconut and palm oil. They are typically solid at room temperature. On average, replacing saturated fat with unsaturated fat tends to lower LDL cholesterol.

Monounsaturated fats are found in olive oil, avocado, and many nuts. They are a hallmark of the Mediterranean dietary pattern and are generally considered heart-healthy.

Polyunsaturated fats include the omega-3 and omega-6 families. These are 'essential' fats; your body can't make them, so you must get them from food. They're found in oily fish, nuts, seeds and vegetable oils.

Trans fats are the genuine villains of the fat world. Small amounts occur naturally in some animal products, but the harmful kind is industrially produced through partial hydrogenation of oils. Trans fats raise LDL cholesterol and lower HDL cholesterol, and are strongly linked to heart disease. They have been largely removed from the Australian food supply, but can still appear in some imported and heavily processed foods.

The modern consensus is less about 'fat good or bad' and more about which fats, replacing what, in the context of an overall dietary pattern.

Saturated Fat: What the Evidence Actually Says

Saturated fat is one of the most contested topics in nutrition. Online, you'll find claims that it has been 'exonerated'. The reality is more nuanced than either extreme.

What's well established is that, on average, saturated fat raises LDL cholesterol, a causal risk factor for cardiovascular disease. What's also true is that the picture depends heavily on what you replace saturated fat with. Major reviews show that replacing saturated fat with polyunsaturated fat lowers heart disease risk, while replacing it with refined carbohydrates and sugar does not (Hooper et al., 2020). In other words, swapping butter for white bread and sugary snacks is not an improvement; swapping it for olive oil, nuts and oily fish is.

The Heart Foundation's position, reflecting this evidence, is that the focus should be on overall dietary pattern rather than single nutrients (Heart Foundation, 2019). They emphasise plenty of vegetables, fruit, wholegrains, legumes, fish, nuts and healthy oils, and recommend limiting foods high in saturated fat (particularly processed foods, fatty and processed meats, and deep-fried takeaways) rather than demonising whole foods like dairy.

It's also worth noting that not all saturated-fat foods behave identically. Whole foods like dairy come with a complex mix of nutrients, and the evidence around full-fat dairy is more neutral than once thought. The strongest, most consistent advice remains: build your diet around minimally processed plant foods, fish and healthy oils, and go easy on processed and deep-fried products.

Seed Oils: Sorting Hype From Evidence

Seed oils (such as canola, sunflower, soybean and safflower oil) have become a lightning rod online, with claims that they are 'toxic' or 'inflammatory'. It's worth separating the genuine considerations from the misinformation.

Seed oils are rich in omega-6 polyunsaturated fats, particularly linoleic acid. The main online concern is that omega-6 fats are pro-inflammatory. However, the actual human evidence does not support the idea that linoleic acid raises inflammation in the body; controlled studies have generally found no increase in inflammatory markers, and higher linoleic acid intake is associated with lower, not higher, rates of heart disease in large population studies (Marklund et al., 2019). When seed oils replace saturated fats, the effect on LDL cholesterol is typically favourable.

Where there is a more reasonable point is context. Much of the seed oil in modern diets arrives via ultra-processed foods, deep-fried takeaways and packaged snacks, foods that are unhealthy for many reasons beyond their oil content. Repeatedly reheated frying oils can also degrade. So the practical concern isn't a bottle of canola oil used at home; it's the overall package of ultra-processed, deep-fried food that seed oils often travel in.

The balanced takeaway: there is no good evidence that using moderate amounts of seed oils in home cooking is harmful, and they're a reasonable choice for replacing saturated fat. Extra-virgin olive oil remains an excellent, well-evidenced everyday choice. The bigger win for most people is cooking more whole foods at home and eating fewer ultra-processed and deep-fried products, regardless of which oil is involved.

Omega-3s and the Omega-6 Balance

Omega-3 fats are genuinely important, and many Australians don't get enough of the most beneficial forms. There are three main omega-3s: ALA, found in plant foods like walnuts, chia, flaxseed and canola; and EPA and DHA, the longer-chain forms found in oily fish such as salmon, sardines, mackerel and tuna. EPA and DHA are the forms most strongly linked to heart and brain health, and the body converts only a small fraction of plant-based ALA into them.

The Heart Foundation recommends eating fish, particularly oily fish, two to three times a week as part of a heart-healthy diet (Heart Foundation, 2019). For people who don't eat fish, including plant sources of ALA regularly is sensible, and a fish oil or algae-based supplement is an option to discuss with a GP.

You'll often hear about the 'omega-6 to omega-3 ratio', with claims that modern diets are dangerously skewed. While it's true that whole-of-population intakes have shifted, the most evidence-based advice is to focus on getting enough beneficial omega-3 (mainly by eating fish) rather than obsessing over the ratio or trying to slash all omega-6. As covered above, the omega-6 fat linoleic acid is associated with lower heart disease risk, so the goal is to increase omega-3, not necessarily to fear omega-6.

Omega-3 status can be measured in the blood, and some people choose to test their omega-3 and omega-6 levels to inform decisions about diet and supplements. As with any test, results are best interpreted alongside your GP and your overall diet.

Understand your cholesterol, not just your diet

The fats you eat are only part of the story; genetics matter too. A lipid blood test shows where you actually stand and helps you and your GP track changes over time.

Start Testing Today

Developed by leading doctorsNo waiting, no referrals2,000+ locations Australia-wide

How the Fats You Eat Show Up in Blood Tests

The clearest way the fats in your diet appear in bloodwork is through your lipid panel, the standard cholesterol blood test. It typically reports several values.

LDL cholesterol (often called 'bad' cholesterol) is the marker most affected by the type of fat you eat. Diets high in saturated and trans fats tend to raise LDL, while replacing them with unsaturated fats tends to lower it. LDL is a well-established causal driver of cardiovascular disease.

HDL cholesterol (often called 'good' cholesterol) helps carry cholesterol away from the arteries. Trans fats lower HDL; healthy lifestyle patterns tend to support it.

Triglycerides are a type of fat in the blood influenced strongly by overall diet, especially refined carbohydrates, alcohol and excess kilojoules, as well as by omega-3 intake, which can lower them.

More advanced markers such as apolipoprotein B (ApoB) and lipoprotein(a) give additional information about cardiovascular risk, and some people choose to measure these alongside a standard panel. Your GP can advise whether they're relevant for you.

It's important to remember that genetics play a large role in cholesterol levels; some people have inherited conditions like familial hypercholesterolaemia that raise LDL regardless of diet. This is one reason blood testing matters: it reveals where you actually sit, rather than where you assume you sit based on diet alone. Lipid results are best reviewed with your GP, who can factor in your family history, blood pressure, weight and other risk factors.

Putting It Into Practice

The practical guidance that flows from the evidence is reassuringly simple, and it aligns with both the Australian Dietary Guidelines and the Heart Foundation.

Choose mostly unsaturated fats. Make extra-virgin olive oil your everyday oil, and include avocado, nuts and seeds regularly. These are well-evidenced, heart-healthy choices.

Eat oily fish two to three times a week. Salmon, sardines, mackerel and tuna provide the beneficial long-chain omega-3s EPA and DHA.

Limit foods high in saturated fat, especially the processed kind. The biggest wins come from reducing fatty and processed meats, deep-fried takeaways, pastries, biscuits and packaged snacks, rather than from cutting whole foods like dairy or eggs.

Avoid industrial trans fats. These are largely gone from the Australian food supply but can appear in some imported and heavily processed foods, another reason to limit ultra-processed products.

Don't fear home cooking oils. Whether you use olive, canola or another common oil at home matters far less than how much ultra-processed and deep-fried food you eat overall.

Know your numbers. A lipid blood test gives you and your GP a baseline and a way to track how dietary and lifestyle changes (and, where needed, medication) affect your cardiovascular risk over time. If you have a family history of high cholesterol or heart disease, this is especially worthwhile.