Is oil "bad" for you?

For years, fat and oil were seen as villains, things to avoid if you were trying to eat healthily. Even now, there are still plenty of proponents of a low-fat or oil-free diet.

 

On the other hand, oils like coconut and avocado are often described as ‘healthy fats’. And the Mediterranean diet, which is known as one of the healthiest in the world, includes plenty of high-quality olive oil.

 

So, what is the truth? Is oil bad for you, or is it something that can be part of a healthy diet? Let’s take a closer look at this confusing issue.

 

Understanding Different Oils

Contrary to popular belief, the fat we get from oils isn’t necessarily a bad thing. Our bodies need some fat to be able to function properly. Fat is an essential energy source, helps you absorb other nutrients, and protects your organs.

 

However, not all forms of fat are made equally. There are four main types (1):

 

  • Monounsaturated 
  • Polyunsaturated
  • Saturated
  • Trans

 

Monounsaturated and polyunsaturated fats typically come from plant-based sources. These include nuts, seeds, beans, and avocadoes. Polyunsaturated fats are also found in oily fish.

 

Plant oils like avocado, olive, coconut, sunflower, and canola contain high levels of unsaturated fats.

 

In contrast, saturated fats are found in animal products, like butter, lard, meat, cheese, milk, and cream.

 

Finally, trans fats are a type of unsaturated fat. Although they do occur naturally in small amounts in meat and dairy, trans fats are most often found in highly processed packaged foods. These are also known as partially-hydrogenated fats. They are created by chemically altering vegetable oils to make them solid at room temperature.

 

Oils and Their Health Impact

One of the most significant ways oils and other fats affect our health is in how they impact our hearts. Saturated fats are linked with higher levels of LDL cholesterol, which raises the risk of cardiovascular disease, including high blood pressure, heart attacks, and strokes.

 

On the other hand, diets that are low in saturated fat and high in polyunsaturated fat appear to be much better for our hearts. 

 

A long-running piece of research called the Seven Countries Study has provided vital evidence for this link (2). The researchers followed large cohorts of people in seven different countries to compare their risk of developing cardiovascular disease.

 

Those in countries like Italy and Japan, where the typical diet includes plenty of monounsaturated and polyunsaturated fat, were at much lower risk of heart disease and stroke than people in the USA and Finland, who ate far more saturated fat.

 

Other studies have found that replacing saturated fats like butter and lard with polyunsaturated fats from plant oils or oily fish can lower our LDL levels and reduce our risk of developing cardiovascular disease (3).

 

Far from being bad for you, some oils can therefore have a protective effect on your heart’s health.

 

Choosing the Right Oils

So, we’ve seen that oils can be good for our health. But there’s another level of consideration when it comes to choosing which oils you include in your diet. And that’s how they react to heat.

 

When oils are heated, they eventually reach their smoking point. At this point, the oil begins to oxidize and release compounds such as free radicals, which are linked with inflammation and an increased risk of cardiovascular disease (4). 

 

Oils that contain a higher level of polyunsaturated fats are more unstable when they are heated and will start to oxidize at lower temperatures. So, we want to avoid these when cooking. That doesn’t mean they should be absent from your diet altogether, just that they are best used raw. 


Examples of oils that are high in polyunsaturated fat include walnut oil, sunflower oil, soybean oil, and corn oil (5).

 

On the other hand, oils that are high in monounsaturated fat are more stable at high temperatures. Olive oil, avocado oil, canola oil, and peanut oil are all good examples (6). 

 

Finally, we also need to consider what type of polyunsaturated fat is present in our oils. There are two main types: Omega-3 and omega-6.

 

Omega-6 fatty acids are thought to have an inflammatory effect on our bodies, potentially increasing our risk of developing chronic diseases (7). In the meantime, omega-3 is anti-inflammatory, protecting our health and helping to prevent illnesses like cancer, arthritis, and cardiovascular disease (8).

 

Flaxseed oil, walnut oil, and hazelnut oil are all high in omega-3. They aren’t great for cooking, since they have a low smoking point. But they are great choices for salad dressings and other raw preparations.

 

So, Are Oils Bad for Us?

As we’ve seen, the answer to this question is a qualified no. When we choose the right oils, they can have a beneficial effect on our health, protecting our hearts and preventing inflammation.

 

However, you do need to choose the oil you use carefully. For cooking, look out for those with a high ratio of monounsaturated fats that make them more stable at high temperatures. When you are eating oil raw, opt for those that are high in omega-3 to get the anti-inflammatory benefits.

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