Note: This is the first article in a new series called “Let’s Talk Tuesday”. You can expect in-depth articles on two Tuesdays per month on varying health and nutrition topics. Today, let’s talk vegetable oils!
Fats are one of the most misunderstood topics in the nutrition world. It wasn’t so long ago that people thought that all fat was bad (hello, 1990’s). Nowadays, just about everybody has come around and agreed that fats like avocados and nuts are healthy. However, there is still quite a bit of disagreement over the types of fats, and whether or not vegetable oil is unhealthy.
You may have heard that vegetable oils, such as corn oil, canola oil, or soybean oil, are healthy fats, but I’m going to provide some reasons as to why this isn’t true.
the basics of fats
Our bodies are dependent on fat! We use fat to make up hormones and cell membranes, for energy, for controlling hunger hormones, and keeping us full. Fat is beneficial because it does not spike blood sugar and may increase metabolism. In addition, fat consumption has been studied for promoting a healthy weight.
Fats are classified by whether they are saturated or unsaturated, however no fats are 100% saturated or 100% unsaturated. All fat-containing foods are combinations of the two. To break it down further, unsaturated fats have categories of monounsaturated (MUFA) or polyunsaturated fats (PUFA). PUFAs can then be primarily classified into omega-3 or omega-6 fats.
saturated fats: the basics
For a brief chemistry lesson, saturated fats do not have double bonds, thus they can stack upon each other. This “stackability” is what allows saturated fat-containing foods to stay solid at room temperature, like butter. These fats are fully saturated, which means that there is no room for any other molecules to bind to it.
Because of this, saturated fats are very stable. We want stable molecules in our body. Saturated fats are most commonly found in animal products, such as butter, dairy and meat. Coconut and palm oil are the main plant sources of saturated fat. Some people don’t process saturated fats very well, which may mean that saturated fats have a negative impact on their blood cholesterol and blood triglyceride (fat) levels. However, most people are just fine with eating saturated fats in moderation.
unsaturated fats: the basics
A monounsaturated fat (MUFA) will have one double bond, which means there one open space for one other molecule to bind to it. These fats are somewhat stable, because another compound, like a free radical, could still come in and bind to that one open spot. Free radicals are unstable molecules that can damage cells and lead to disease and accelerated aging. MUFAs are typically found in plant foods, like olive oil and avocados. In general, monounsaturated fats are very healthy fats to consume.
Polyunsaturated fats (PUFAs) have multiple double bonds, which means they have multiple open spots for free radicals to bind to. This makes them very unstable and able to cause inflammation when they are exposed to heat or light. Fatty fish and vegetable oils typically contain PUFAs. The structure of these fats makes them prone to oxidation, which is the opposite of what we want in our bodies. We want antioxidants! PUFAs can be very healthy fats, as long as they are not damaged from free radicals. For example, the PUFAs found in salmon or flaxseeds are very healthy fats.
why vegetable oil is unhealthy
Vegetable oils, including corn oil, soybean oil, canola oil, peanut oil, cottonseed oil, safflower oil, sunflower oil, and grapeseed oil, are all primarily PUFAs. These foods go through an extensive process to make oil out of them. When you think about a kernel of corn, you can imagine that it is not very oily, and would take a lot of work to make oil out of it, compared to an olive or an avocado.
The process of making vegetable oil includes mechanical pressing, bathing in a hexane solution, degumming, bleaching, and deodorizing. All of these steps occur before it can become a store-ready oil.
Any or all of these steps could introduce high heat or light, which is what causes these oils to become oxidized, or rancid. Due to their unstable structure and highly processed nature, vegetable oils are unhealthy fats, despite what national guidelines may say.
health impacts of oxidation
Oxidized fats have detrimental effects on our health. Oxidation is related to inflammation, and inflammation is at the core of all chronic diseases, like heart disease, cancer, diabetes, and obesity.
Oxidation can occur in healthy fats as well, like if you cook at high heats with olive oil, or if your fish oil pills go rancid. Keep in mind that polyunsaturated fats are very fragile, and should be treated in a fragile way.
This means only using olive oil, sesame oil, walnut oil, or macadamia nut oil for dressings or when cooking at very low temperatures. Similarly, this means avoiding the vegetable oils mentioned above, as they are already damaged when they get to the store due to the processing methods mentioned earlier.
omega-3 and omega-6 fats
Let’s talk a little about omega-3 and omega-6 fats. In general, omega-3 fats are anti-inflammatory, while omega-6 fats tend to promote inflammation. Both of these fats are essential in our bodies and we need them in our diet.
However, these fats compete in the body for space, resulting in the ratios of them becoming skewed in an unfavorable way over the past few decades. Our ancestors used to have a ratio of about 1:1 for omega-3 to omega-6 in their diets. Today, the ratio goes up to 1:25 for omega-3 to omega-6. Many researchers say a ratio of about 1:4 would be ideal today.
This overconsumption of omega-6 fats leads to more inflammation in the body. The top source of omega-6 fats in the American diet is from vegetable oils.
One way to balance out this ratio is by reducing your intake of vegetable oils, while increasing your intake of fatty fish (such as salmon, sardines, tuna, and mackerel), walnuts, chia seeds, and flaxseeds. Whole nuts and seeds are a better choice to get your omega-6 fats in, as opposed to processed seed and vegetable oils.
saturated fat and health
Saturated fat has received a bad reputation in recent decades. However, the latest research is showing that there is no clear link between saturated fat intake and heart disease in the majority of people.
There are many aspects of saturated fat that actually make it healthy for us. Saturated fat is the main fat composing our cell membranes. This is beneficial because they are stable and don’t oxidize easily (we don’t want unstable cell membranes). Similarly, saturated fats are great for cooking for this same reason. The high heat doesn’t create rancid fats through oxidation because of its stability. Saturated fats have been consumed for centuries without problem. For example, about 50% of the fat in breast milk is saturated fat!
However, saturated fat, like most foods, is good to consume in moderation. There may be an negative impact on the gut microbiome in people who consume excessive amounts of saturated fat. Above all, saturated fat is still a better choice than an unhealthy vegetable oil.
This may be different from what you’ve heard from mainstream nutrition guidelines. Nutrition research is always changing and growing. As a result, sometimes it can take many years for updated guidelines to come out. On average, it takes 17 years for new research to make its way into clinical guidelines.
key takeaways:
- In conclusion, most fats are very healthy for us to consume.
- However, the processing of some unsaturated fats, like vegetable oils, can make them unhealthy options.
- For example, the high-heat and extensive processing of vegetable and seed oils creates unstable, rancid, and inflammatory compounds that can build up in our bodies, making vegetable oil an unhealthy fat.
- The best fats for cooking with are coconut oil, grass-fed butter, ghee, or avocado oil. These are all saturated fats.
- The best fats for dressing or using in very-low-heat cooking are olive oil, sesame oil, walnut oil, and macadamia nut oil.
- Food sources of healthy fats include avocados, fatty fish, olives, nuts and seeds, coconut products, full-fat dairy, and humanely raised meats.
- Avoid products containing unhealthy vegetable oil, soybean oil, canola oil, corn oil, and cottonseed oil.
Check out some of my favorite recipes using healthy fats, like olive oil, grass-fed butter, and avocado.
additional references:
Shanahan, Cate. (2017). Deep Nutrition. New York, NY: Flatiron Books.
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