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The Unspoken Truth About Vegetable Oils: What You Need to Know

ByHuman Health Co.

Since the 1960s, large health associations and food manufacturers have praised the health benefits of vegetable oils. As their popularity grew, producers eagerly marketed their supposed health benefits—despite little to no scientific evidence supporting these claims. Now, as more people research food and health independently, the truth is emerging: we’ve been misled from the start. In this article, we reveal the unspoken truth about vegetable oils.

How It’s Made

Vegetable Oils

A vast golden wheat field stretches under a bright blue sky with fluffy clouds.

First, we should clarify that there are no vegetables in “vegetable” oils. These oils come from seeds and plant material that would have otherwise been discarded. Vegetable oils gave manufacturers a way to turn their trash into a billion-dollar industry. Common vegetable oils include canola, corn oil, soybean, cottonseed, rapeseed, and safflower.

Seeds and plant material are not high in natural fat or oil. So what little fat they do have has to be crushed and chemically extracted, typically with a chemical called Hexane1. Hexane is a chemical made from crude oil that has an odor similar to gasoline2. Along with the production of vegetable oils, it has many industrial uses including:

  • Cleaning agents in the printing, textile, furniture, and shoemaking industries
  • Adhesives: Special glues used in roofing, shoe, and leather industries
  • A component of quick-drying glues and rubber cement
  • A component of gasoline

The plant material is heated with hexane to extract the oils. After extraction, the oils undergo a bleaching process to remove impurities, eliminate odors, and improve texture. Some oils are further processed through hydrogenation, where a metal catalyst (usually nickel) is used to bond hydrogen to the carbon double bonds in unsaturated fat. This process transforms liquid vegetable oil into a solid form, like margarine.

Animal-Based Oils/Fats

Animal fats include butter, lard, tallow, ghee, duck fat, bacon grease, suet, and other fats rendered from animal products. These fats are solid at room temperature but melt when heated. There are different methods for producing animal fat.

Fats from animal tissue are rendered by cutting the fatty tissue into small pieces and boiling or steaming it to extract the fat. The remaining tissue is pressed to remove any leftover fat, which is then cooked to eliminate water, kill pathogens, and improve shelf stability. In some cases, the rendered fat is bleached to enhance color and texture.

Fats from animal-based products, like milk, are processed differently. To make butter, the cream is first separated from the milk and pasteurized to kill bacteria. It is then churned to break down fat membranes, allowing the fat to clump together and form butter. The leftover liquid is known as buttermilk.

Effects of Vegetable Oils on the Body

Vegetable oil consumption is common worldwide due to its affordability and versatility in cooking. However, while vegetable oils are inexpensive financially, they can carry a high cost to health.

When vegetable oils are heated and reheated, their harmful effects increase significantly. Heating vegetable oils—whether during manufacturing or cooking—causes lipid oxidation, leading to rancidity. Lipid oxidation has been linked to chronic conditions3, such as diabetes4, cancer, dementia, rheumatoid arthritis, atherosclerosis, and tissue and cell damage.

A study of rats5 fed previously heated vegetable oils found an increase in cholesterol, glucose, and creatine. Increased cholesterol with increased glucose leads to arterial damage causing clogged arteries and potentially stroke or heart attack. Increased creatine indicates kidney damage or disease. The rats in this study were also found to have a significant increase in oxidative stress6. A phenomenon that leads to cell damage and is linked to conditions such as cancer, Alzheimer’s disease, inflammation in the body, hormone imbalance, and heart disease.

Oxidative Stress

Oxidative stress is a popular topic in health science. It is widely known that sources of oxidative stress like UV light, ionizing radiation, heavy metals, and environmental pollutants can lead to serious health problems. Completely avoiding these sources can be difficult, which is why it’s important to reduce other avoidable sources of oxidative stress.

Oxidative stress is a relatively complex condition that happens on a cellular level. It occurs when there are too many free radicals in the body and not enough antioxidants to neutralize them. Free radicals are unstable molecules that build up in cells and damage DNA, lipids, and protein molecules. Growing evidence shows that oxidative stress plays a significant role in the onset and progression of chronic health conditions such as diabetes, hypertension, ischemic heart disease, and chronic heart failure7.

It is well known that DNA damage caused by oxidative stress can promote the development of cancer. Oxidative stress can also lead to chromosomal abnormalities, which are associated with cancer growth, and the development of oncogenes8. Oncogenes are mutated genes that drive the formation of cancer. Studies have found a strong correlation between cancer death rates and the consumption of vegetable oils. The good news is, that oxidative stress caused by vegetable oils can be avoided.

Healthy Vegetable Oil Options

There are some healthy vegetable and fruit oils. Vegetable oils that come from actual fatty vegetables and fruits, such as olives, avocado, coconut, and palm oil are generally considered healthy to eat. If possible opt for the organic, cold-processed versions of these fats.

It’s important to check the smoke point of each oil before cooking with it to ensure you are not overheating it. Beware of products labeled with terms such as “made with olive oil”. Often these products contain olive oil as well as canola or other unhealthy vegetable oils. Always be sure to read your food labels before buying.

The Unspoken Truth About Vegetable Oils

The reality is that vegetable oils are inherently harmful to your health, and it’s best to avoid them entirely. However, given their widespread use in processed foods and cooking, this can be challenging. Try to avoid buying products that list any type of vegetable oil in the ingredients.

Person Pouring cooking Oil in a Pan

When eating out, ask about the oils used in cooking and avoid dishes prepared with vegetable oils whenever possible. While the body can tolerate small amounts of vegetable oil occasionally, regular consumption greatly increases the risk of chronic health issues.

For optimal health, aim to keep vegetable oils to 5% or less of your total fat intake. The remaining 95% should come from animal-based fats or healthy oils from fruits and vegetables, such as olive, avocado, coconut, and palm oil.

Supporting Research

  1.  National Center for Biotechnology Information (2024). PubChem Compound Summary for CID 8058, n-HEXANE. Retrieved August 20, 2024 from https://pubchem.ncbi.nlm.nih.gov/compound/n-HEXANE. ↩︎
  2. Environmental Protection Agency (EPA). (n.d.). Hexane. https://www.epa.gov/sites/default/files/2016-09/documents/hexane.pdf ↩︎
  3. Ansell MDFACC, B. J., & Fonarow MDFACC, G. C. (2005). Lipid Oxidation. Lipid Oxidation – an overview | ScienceDirect Topics. https://www.sciencedirect.com/topics/medicine-and-dentistry/lipid-oxidation#:~:text=Lipid%20oxidation%20is%20associated%20with,variety%20of%20biologically%20active%20compounds. ↩︎
  4. Human Health Co. (2025a, January 20). The Complete Guide to Understanding the Causes of Diabetes. https://humanhealthco.com/the-complete-guide-to-understanding-what-causes-diabetes/ ↩︎
  5. Perumalla Venkata R, Subramanyam R. Evaluation of the deleterious health effects of consumption of repeatedly heated vegetable oil. Toxicol Rep. 2016 Aug 16;3:636-643. doi: 10.1016/j.toxrep.2016.08.003. PMID: 28959587; PMCID: PMC5616019. ↩︎
  6. Pizzino G, Irrera N, Cucinotta M, Pallio G, Mannino F, Arcoraci V, Squadrito F, Altavilla D, Bitto A. Oxidative Stress: Harms and Benefits for Human Health. Oxid Med Cell Longev. 2017;2017:8416763. doi: 10.1155/2017/8416763. Epub 2017 Jul 27. PMID: 28819546; PMCID: PMC5551541. ↩︎
  7. Taniyama Y, Griendling KK. Reactive oxygen species in the vasculature: molecular and cellular mechanisms. Hypertension. 2003 Dec;42(6):1075-81. doi: 10.1161/01.HYP.0000100443.09293.4F. Epub 2003 Oct 27. PMID: 14581295. ↩︎
  8. Pizzino G, Irrera N, Cucinotta M, Pallio G, Mannino F, Arcoraci V, Squadrito F, Altavilla D, Bitto A. Oxidative Stress: Harms and Benefits for Human Health. Oxid Med Cell Longev. 2017;2017:8416763. doi: 10.1155/2017/8416763. Epub 2017 Jul 27. PMID: 28819546; PMCID: PMC5551541. ↩︎

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