Good Oils vs. Bad Oils: Understanding the Health Implications of Dietary Fats

Reviewed by Jeremie Walker, MD, MBA · May 22, 2023
good oils vs. bad oils for your health

The role of dietary fats in human health has been a topic of extensive research and debate in recent years. While some fats positively affect human health, others can have a more negative impact. This article explores the differences between “good” and “bad” fats, their sources, and their potential effects on your health. We will review the scientific literature on the health effects of different types of fats and provide evidence-based recommendations for selecting the most healthful oils for cooking and consumption. 

The information presented in this article aims to inform and empower individuals to make informed choices about the fats they use in their diets, with the goal of promoting overall health and well-being.

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Not All Fat Is Bad

Fat (including the fat in oils) often gets a bad reputation. But we need a good level of healthy fats in our diet. Over recent years the American Heart Association and federal dietary guidelines have moved away from the idea of limiting fats in your diet to eating an overall healthy diet and choosing good fats. A good way to get healthy fats into your diet is to choose a whole-food diet where your fats are coming from sustainably raised plants and animals. You typically want to avoid the more refined and processed commercial seed oils (including canola, corn, soybean, vegetable, safflower, etc.)  as they can cause more harm to your health. 

An overview of cooking oils

There are a lot of different cooking oils out there, and it can be challenging to know what to choose. You’ve undoubtedly seen headlines online either stating that a particular oil is terrible for you or good for you. It isn’t very clear. So let’s start at the beginning to understand some basic differences between the fats at our disposal.

The composition of the fats we cook in determines their stability under heat, flavor profiles, and smoke points. Here is a breakdown of the four main types of fats found in our cooking fats and oils. 

  • Monounsaturated fats: These are characterized by a single, double bond in their structures, are liquid at room temperature, and are stable under heat. Good oils to cook in that are high in monosaturated fats are olive oil and avocado oil. Although many seed oils (canola, corn, soybean, etc.) have monounsaturated fats, they are not good oils to cook in for reasons we will discuss later.
  • Polyunsaturated fats: These are characterized by more than one double bond in their structure, are also liquid at room temperature, and are very unstable under heat. You are probably more familiar with this than you think, especially if you have heard of Omega-3 and Omega-6 fatty acids. That’s exactly what they are. Also found in abundance in the above seed oils. 
  • Saturated fats: These are characterized by no double bonds in their structure and are very stable under heat. Therefore saturated fats are the best fats to cook in, especially when subjected to high and long heating periods. Examples of saturated fats include butter, ghee, coconut oil, tallow, and lard. The most current review of old and new evidence, contrary to the lingering belief, is that saturated fats are not a cause of heart disease.
  • Trans fats: There are natural trans fats derived from animal products (the only good kind of trans fat) and artificial trans fats (not good and used to make liquid fats solid at room temperature, like margarine and Crisco). The artificial trans-fats are also found in lesser quantities in commercial liquid seed oils (corn, canola, soybean, vegetable, safflower, etc). Trans fats in general are characterized by a particular type of double bond. However, they are mostly man-made in today’s food system and are very harmful. 

The framework for any successful nutritional plan should include a variety of whole foods that are prepared in the good fats mentioned above and below. Let’s keep going………

The smoke point

The structure of an oil can change when heated. And some oils are more suited to cooking at higher temperatures than others. How much an oil changes under heat is very dependent on the type of oil, how long it’s heated, and the temperature used. 

If an oil starts to burn, this is known as its smoke point. An oil’s smoke point is not necessarily related to its stability under heat. For example, butter is a very stable saturated fat but has a low smoke point (350F) when compared to ghee (480F) which is also a saturated fat. Smoke point is more related to “flavor” than a change in oil composition or structure. Sounds odd, right! However, we do know that all non-saturated fats can become more toxic when heated because of their anatomy (double bonds vs no double bonds). When the oil breaks down, it can form harmful compounds such as aldehydes and more trans-fats—compounds strongly linked to conditions like heart disease and cancer. 

However, what matters the most is not the smoke point but the stability of the fat under heat, so:

  • Saturated fats (no double bonds, stable under heat)
  • Monounsaturated fats (1 double bond, less stable under heat)
  • Polyunsaturated fats (2 or more double bonds, not stable under heat)

Another element of the “cooking oils” to consider is whether they contain antioxidants. Antioxidants have a crucial function in safeguarding oils from oxidation, an undesirable process that can occur when oils are subjected to heat. That’s why good extra virgin olive oil (smoke point 350F) is safer than commercial seed oils mentioned above. Consequently, antioxidants play a significant role in preserving the stability of oils and ensuring their health-enhancing properties. That’s why some might argue extra virgin olive oil is better for you when consumed in its raw and native state, like on a salad or atop a piece of bread (before heated and oxidized)

How oil is processed

The processing of oils must also be considered. Minimally processed oils tend to be referred to as unrefined oils. Oils such as virgin or extra virgin olive oil are not processed using chemicals, and cold-pressed oils are not made using heat. These types of methods allow the oil to retain its nutritional benefits. On the other hand, refined oils that are processed using heat or chemicals lose their nutritional benefits. 

The oxidative stability of oils decreases as they undergo greater refinement, primarily due to exposure to high temperatures, which leads to the removal of natural antioxidants and introduces trans fats.

What cooking oil to choose?

Let’s look at some specific oils and fats to cook with and which are more beneficial for health than others. 

Olive oil

A famous staple in the Mediterranean diet, olive oil has long been associated with many health benefits. One of the main benefits of olive oil is its ability to reduce the risk of cardiovascular disease. According to a study published in the New England Journal of Medicine, individuals who consumed a Mediterranean diet rich in olive oil had a 30% lower risk of heart disease. 

Plus, it has been shown to have anti-inflammatory properties that can help reduce the risk of chronic diseases such as cancer and Alzheimer’s disease. It is a source of at least 30 phenolic compounds that benefit human health due to their potential antioxidants.

Virgin and extra virgin olive oils are processed without chemicals, ensuring they keep their nutrient content, including polyphenols and nutrients like vitamin E. Although unrefined extra virgin olive oil has a lower smoke point of 350⁰ – 410⁰ F, it is suitable enough for lighter home cooking. Also, it is loaded with antioxidants. Not only are these very healthy, but they also improve the resistance to oxidative damage while under heat. So, it’s a great choice of oil to cook with. Overall, incorporating olive oil into your diet can provide numerous health benefits and help promote overall wellness.

Key things to look for to ensure you are buying good quality olive oil are:

  • Extra Virgin Olive Oil
  • Single Origin Olive Oil
  • Cold Pressed Olive Oil
  • Packaged in a dark-colored glass bottle and has a “pressed on” date

Avocado oil

Avocado oil is another great choice for cooking as it contains monounsaturated and polyunsaturated fatty acids and vitamin E. Vitamin E is a powerful antioxidant that helps protect cells from damage caused by free radicals. It may have anti-inflammatory properties and can contribute to skin health. It’s unrefined like extra-virgin olive oil meaning it isn’t highly processed and maintains a very good nutritional value at both low and high temperatures. So if you like avocados, this is a good one to try. It’s a great option for salad dressings also. 

Avocado oil primarily consists of monounsaturated fats, which contribute to its stability when exposed to heat. However, it has relatively low antioxidant content when compared to olive oil, which means it has limited resistance to oxidation. While avocado oil remains stable at moderate heat, it is prone to oxidizing over extended periods. 

If you decide to use avocado oil, look for pure avocado oil and avoid the ones that are potentially cut with inferior seed oils. A recent review of avocado oils found some shocking results of what you get on the store shelves. Always, buyer beware. 

Coconut oil

Coconut oil is quite a controversial one. While some people claim that it has numerous health benefits, others argue that it is not as healthy as once advertised. 

One of the main concerns about coconut oil is its high saturated fat content, and saturated fat was once believed to be unhealthy. According to the American Heart Association, 82% of coconut oil fat is saturated, significantly higher than butter (63%) and beef fat (50%).

The specific types of saturated fats found in coconut oil, such as lauric acid, may have potential health benefits. Coconut oil has been associated with raising levels of high-density lipoprotein (HDL) cholesterol, which is often referred to as “good” cholesterol. It also contains medium-chain triglycerides (MCTs), which are quickly metabolized by the body and can be a source of readily available energy. It also has antioxidant properties that may prevent oxidative stress, which can cause cardiovascular health problems. So don’t assume coconut oil is bad.   

As coconut oil is very high in saturated fat, it is very stable at high heat. Although, it does have a low smoke point of 350 degrees which could impact the flavor of the foods you cook. Overall, if you enjoy cooking with coconut oil, there is no harm in enjoying it as part of a balanced diet. 

Flaxseed Oil

Although we’ll go into more detail below about why you should avoid most seed oils, flaxseed oil has many benefits. It is extracted from the seeds of the flax plant and is a rich source of alpha-linolenic acid (ALA), an essential omega-3 fatty acid that the body cannot produce. Although packed with nutrients, flaxseed oil is not one to use for cooking or frying as it has a low smoke point and is highly prone to oxidation, which can create harmful compounds. 

However, you can use flaxseed oil as a finishing oil, such as in salad dressings or smoothies. According to the  Arthritis Foundation, ground flaxseed is an exceptional source of inflammation-reducing omega-3 fatty acids and lignans, a cancer-fighting plant chemical. With just two tablespoons of ground flaxseed, you can obtain more than 140% of the daily value of omega-3 fatty acids and the highest concentration of lignans found in any other plant food. However, we must note that although you get 140% of an omega-3 called ALA, the body can only convert about 5% of this to the more important omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Therefore, it’s imperative to consume EPA/DHA found in animal products like fish and eggs or algae to get the required amounts. 

When considering oils, flaxseed is an excellent addition to a healthy, balanced diet- just remember not to cook with it. You also need to remember to look for pure, unrefined flaxseed oil, such as ones that are cold-pressed. 

A note on butter and tallow

Although we’re focusing on oils in this article, it would be remiss not to discuss cooking with butter and tallow. Butter and tallow are both sources of healthy saturated fats. Due to their high saturated fat content, they remain stable at heat.

Look for butter from grass-fed animals where possible. This contains conjugated linoleic acid, a type of fatty acid which studies show may have anti-inflammatory properties. It’s also rich in vitamins A and K2 and Omega 3 fatty acids (26% more Omega 3 than regular butter). Vitamin K2 plays a vital role in bone and heart health. You can also get 100% grass-fed tallow, ensuring the best quality fat.

The key when picking fats to cook with is looking for whole, minimally processed, nutritious food as close to its natural form as possible. 

Interested in learning about TRT? Find out more from Opt Health!

Oils to reduce or avoid in your diet

Seed Oils

Seed oils are not inherently bad for you, but they can be less healthy than other types of oils due to their composition and processing methods. Consumption and cooking in refined seed oils like canola, corn, soybean, vegetable, and safflower can be cumulatively very detrimental to your health long-term. 

Many seed oils are high in omega-6 fatty acids, which are essential but should be consumed in balance with omega-3 fatty acids. Evidence indicates that the ratio of omega-6 to omega-3 fats in the diet of our hunter-gatherer ancestors was approximately 1:1. However, in the Standard American Diet, the ratio ranges from an average of 10:1 to 20:1. Excessive intake of omega-6s can lead to inflammation in the body and increase the risk of chronic diseases such as heart disease and cancer.

In addition, some seed oils undergo significant processing, including high-heat extraction and chemical refining, which can strip them of their natural antioxidants and nutrients and leave behind harmful compounds like trans fats. The use of solvents in the extraction process can also result in residual solvent contamination.

Seed oils are commonly used in processed foods (crackers, chips, salad dressings) and restaurants due to their affordability, mild flavor, and high smoke points. However, their prevalence in these products is a cause for concern due to their high omega-6 content and processing methods that can lead to the presence of harmful compounds. So remember to consider this when eating out or shopping for groceries, and always read the ingredient labels. 

It’s important to note that not all seed oils are created equal. Some, like cold-pressed flaxseed oil, are high in omega-3 fatty acids and are considered beneficial. It’s always best to choose minimally processed, organic oils and use them in moderation as part of a healthy, balanced diet.

Palm oil 

Palm oil is a commonly used cooking oil in many parts of the world, like Asia or Africa, but it is associated with various health risks. Here are some reasons that explain why palm oil isn’t healthy to cook with:

  1. High in Trans Fats: The process of refining palm oil can create trans fats, which are known to be harmful to human health. According to the World Health Organization, trans fat intake is responsible for up to 500 000 premature deaths from heart disease annually.
  2. Low in Nutrients: Compared to other cooking oils, palm oil is low in essential nutrients such as vitamins, minerals, and antioxidants. 
  3. Linked to Environmental Issues: Palm oil production has been linked to deforestation, habitat destruction, and biodiversity loss. It is estimated that palm oil plantations are responsible for up to 10% of global greenhouse gas emissions.
  4. Potentially Carcinogenic: Palm oil is often refined at high temperatures, which can create a carcinogenic substance called glycidol. Palm oil contains higher levels of glycidol than other vegetable oils, which may increase cancer risk.

In conclusion, using palm oil as a primary cooking oil is not recommended due to its high content of saturated and trans fats, low nutrient density, and potential health and environmental risks.

Partially hydrogenated oil

Partially hydrogenated oil is a type of oil that is commonly used in processed foods such as baked goods, snacks, and fried foods. However, as mentioned at the beginning of this article, it has a high content of trans fats. And as we know, trans fats are linked to an increased risk of heart disease, stroke, and type 2 diabetes.

In fact, the FDA has banned the use of partially hydrogenated oil in foods as of June 2018 due to its health risks. Eliminating partially hydrogenated oil from the food supply could prevent up to 20,000 heart attacks and 7,000 deaths from heart disease each year in the United States. Thus, it is crucial to avoid consuming foods that contain partially hydrogenated oils to protect our health.

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