When people think about the causes of inflammation, weight gain, or metabolic dysfunction, most zero in on sugar or processed carbs. But one of the biggest culprits may be lurking in your cooking oil. The kind of fat you eat, and more importantly, the kind you don’t even know you’re eating, can have a massive impact on your fat loss, hormonal health, and long-term inflammation levels.
Even if you eat clean at home, dining out or relying on store-bought products could be exposing you to processed fats every single day. These seed oils are cheap, flavorless, and nearly impossible to avoid in modern restaurants, packaged foods, and salad dressings. The consequences, however, are anything but subtle.
Let’s take a closer look at why these oils matter, how they impact your body, and what to do about them.
What Are Processed Fats (and Why Are They Everywhere)?
Processed fats refer to industrial seed and vegetable oils that go through heavy chemical and mechanical processing before reaching your plate. These include:
- Soybean oil
- Corn oil
- Canola oil
- Safflower oil
- Cottonseed oil
- Sunflower oil
- Margarine and shortening
They’re extracted using high heat and solvents like hexane, then deodorized and refined to mask their rancid smell and taste. This process damages the oils, creates oxidized byproducts, and dramatically increases their omega-6 content. All of which promote inflammation when consumed in excess (1).
Why are they everywhere? They’re cheap, shelf-stable, and blend well into processed foods. Restaurants often fry, sauté, and drizzle them over nearly every item on the menu including items labeled “healthy.”
How Processed Oils Promote Inflammation
The biggest issue with seed oils isn’t that they’re fats—it’s the kind of fat they contain. Most processed oils are rich in omega-6 polyunsaturated fatty acids (PUFAs). While omega-6 fats aren’t inherently bad, they must be balanced with omega-3s to maintain a healthy inflammatory response.
The modern Western diet has skewed that ratio far out of balance. While our ancestors ate omega-6 and omega-3 fats in a ratio close to 1:1, today’s average intake is closer to 20:1 or even 25:1 in favor of omega-6 (2). This imbalance is linked to:
- Chronic low-grade inflammation
- Increased insulin resistance
- Greater risk of obesity, heart disease, and type 2 diabetes (3)
- Impaired mitochondrial function, which reduces energy output and recovery (4)
This kind of systemic inflammation doesn’t just impact your health. It interferes with fat loss, slows recovery, and disrupts hunger and energy regulation.
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Processed Fats and Fat Storage
Chronic inflammation interferes with fat loss by activating the immune system in a way that signals your body to hold on to fat. It also elevates cortisol and disrupts insulin sensitivity, making it harder for your cells to burn fat efficiently (5). This is especially relevant for people who are training hard but not seeing results.
Studies have shown that high intake of omega-6-rich oils promotes fat accumulation in both liver and visceral tissues, which are more strongly associated with metabolic dysfunction than subcutaneous fat (6).
Even worse, many of these oils are used in deep-frying, a process that creates additional oxidative stress in the body. Reheated oils, like those used in fast food fryers, can produce trans fats and aldehydes that further damage cells, increase cardiovascular risk, and impair fat metabolism (7).
Don’t Be Fooled by the Label
Many products that sound healthy still contain hidden seed oils. Look out for:
- “Heart-healthy” snacks
- Plant-based butters
- Store-bought hummus or pesto
- Vegan protein bars and shakes
- Sauces and salad dressings
- Roasted nuts and nut butters
Even the term “vegetable oil” is often just a generic label for soybean or corn oil. It’s not about demonizing fat. It’s about understanding the type and the source.
What to Use Instead
For cooking and eating at home, stick with fats that are stable, minimally processed, and lower in omega-6:
- Extra virgin olive oil
- Avocado oil
- Coconut oil (in moderation)
- Grass-fed butter or ghee
- Animal fats like beef tallow or duck fat (when from clean sources)
These fats are more resistant to oxidation, have better fatty acid profiles, and contain bioactive compounds that support inflammation control, brain health, and hormone function (8).
When eating out, you may not be able to control the oil used, but you can:
- Ask for food grilled or baked instead of fried
- Request olive oil and vinegar as dressing
- Avoid items with creamy sauces or deep-fried ingredients
- Choose simpler menu items with fewer processed components
✏︎ The Bottom Line
Processed seed oils like soybean, canola, and corn oil are cheap, flavorless, and often invisible. But their effects on your metabolism, hormones, and fat loss are anything but. These oils promote inflammation, disrupt fat metabolism, and can silently sabotage your progress even if you’re “eating clean.”
You don’t need to obsess or avoid dining out. But making smarter choices at home and staying aware of hidden oils in processed foods can dramatically reduce your inflammation levels and help your body respond better to your fat-loss plan.
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Bibliography
- Kamel, B. S., and Y. Kakuda. “Fatty Acid Composition of Edible Oils and Fats: Nutritional and Technological Implications.” Nutrition Reviews, vol. 72, no. 12, 2014, pp. 773–785. https://www.sciencedirect.com/science/article/abs/pii/S1537189114000536
- Simopoulos, Artemis P. “The importance of the omega-6/omega-3 fatty acid ratio in cardiovascular disease and other chronic diseases.” Experimental biology and medicine (Maywood, N.J.) vol. 233,6 (2008): 674-88. doi:10.3181/0711-MR-311. https://pubmed.ncbi.nlm.nih.gov/18408140
- Patterson, E et al. “Health implications of high dietary omega-6 polyunsaturated Fatty acids.” Journal of nutrition and metabolism vol. 2012 (2012): 539426. doi:10.1155/2012/539426. https://pmc.ncbi.nlm.nih.gov/articles/PMC3335257/
- Rohrbach, S. “Effects of dietary polyunsaturated fatty acids on mitochondria.” Current pharmaceutical design vol. 15,36 (2009): 4103-16. doi:10.2174/138161209789909692. https://pubmed.ncbi.nlm.nih.gov/20041812/
- Gregor, Margaret F, and Gökhan S Hotamisligil. “Inflammatory mechanisms in obesity.” Annual review of immunology vol. 29 (2011): 415-45. doi:10.1146/annurev-immunol-031210-101322. https://pubmed.ncbi.nlm.nih.gov/21219177/
- Alvheim, Anita R et al. “Dietary linoleic acid elevates endogenous 2-AG and anandamide and induces obesity.” Obesity (Silver Spring, Md.) vol. 20,10 (2012): 1984-94. doi:10.1038/oby.2012.38. https://pubmed.ncbi.nlm.nih.gov/22334255/
- Moumtaz, Sarah et al. “Toxic aldehyde generation in and food uptake from culinary oils during frying practices: peroxidative resistance of a monounsaturate-rich algae oil.” Scientific reports vol. 9,1 4125. 11 Mar. 2019, doi:10.1038/s41598-019-39767-1. https://pmc.ncbi.nlm.nih.gov/articles/PMC6412032/
- Hu, F B et al. “Types of dietary fat and risk of coronary heart disease: a critical review.” Journal of the American College of Nutrition vol. 20,1 (2001): 5-19. doi:10.1080/07315724.2001.10719008. https://pubmed.ncbi.nlm.nih.gov/11293467/
