What is the unhealthiest oil to consume? A guide to making better choices

October 16, 2025 •

4 min read

According to the World Health Organization, more than 540,000 deaths every year can be attributed to industrially produced trans fats, making understanding what is the unhealthiest oil to consume a critical step in improving your diet and protecting your heart health. These fats hide in many processed foods and have severe, well-documented health consequences.

Quick Summary

Industrially produced trans fats, from partially hydrogenated oils, are the most harmful oils for health, significantly raising bad cholesterol and increasing the risk of heart disease and inflammation. Limiting processed foods and opting for healthier fats is key for better nutrition.

Key Points

Worst Oil: Partially hydrogenated oils, containing artificial trans fats, are the most dangerous oils to consume due to their severe negative effects on heart health.
Heart Health Risks: Trans fats significantly increase "bad" LDL cholesterol while decreasing "good" HDL cholesterol, greatly raising the risk of heart attacks, stroke, and type 2 diabetes.
Chronic Inflammation: Highly refined vegetable oils high in omega-6s, like soybean and corn oil, can cause chronic inflammation when the intake is imbalanced with omega-3s.
Hidden Dangers: Partially hydrogenated oils are frequently found in processed foods such as packaged baked goods, fried items, and certain margarines.
Label Reading is Key: Look for "partially hydrogenated oil" on ingredient lists. Even products labeled "0g trans fat per serving" can contain small, accumulated amounts.
Healthier Alternatives: Use cold-pressed oils like extra virgin olive oil and avocado oil, which are rich in healthy monounsaturated fats and antioxidants.
Avoid Reheating: Repeatedly heating any oil, especially for deep frying, can break it down and produce harmful trans fats and toxic compounds.

For anyone focused on a healthy diet, understanding the quality of the fats consumed is crucial. While many oils offer valuable nutritional benefits, some pose a significant threat to your health. Industrially produced trans fats, derived from partially hydrogenated oils, stand out as the definitive answer to the question: what is the unhealthiest oil to consume? They have no known health benefits and are linked to a host of chronic diseases.

The Dangers of Trans Fats from Partially Hydrogenated Oils

Trans fats are created through a process called partial hydrogenation, where hydrogen is added to liquid vegetable oil to make it more solid and increase its shelf life. This industrial modification is what creates the highly damaging trans fatty acids. The health impacts are so severe that the FDA determined partially hydrogenated oils were no longer "generally recognized as safe" for use in human food, with a ban on their use by food manufacturers starting in 2018.

Impact on Cholesterol

The most significant and well-documented effect of trans fat consumption is its impact on cholesterol levels. Unlike other fats, trans fats have a dual negative effect on heart health:

They raise low-density lipoprotein (LDL) cholesterol, often called "bad" cholesterol, which contributes to the buildup of fatty deposits in arteries, making them hard and narrow.
They lower high-density lipoprotein (HDL) cholesterol, or "good" cholesterol, which helps clear excess cholesterol from the arteries and transports it back to the liver for removal.

Inflammation and Disease Risk

Beyond cholesterol, trans fats promote inflammation throughout the body. Chronic inflammation is a known risk factor for many serious conditions, including:

Heart disease and stroke
Type 2 diabetes
Obesity
Certain cancers

Beyond Trans Fats: Other Oils to Watch

While trans fats are the worst offenders, other oils can be detrimental to health depending on their composition and how they are processed. Heavily refined vegetable oils often have an imbalanced omega-6 to omega-3 fatty acid ratio, which can promote inflammation if consumed in excess.

The Problem with an Imbalanced Omega Ratio

Both omega-6 and omega-3 fatty acids are essential for health, but they must be in balance. Modern diets, heavily reliant on processed foods containing oils like soybean, corn, and refined sunflower, have skewed this ratio significantly, with excess omega-6 intake promoting inflammation.

Soybean Oil: A common and inexpensive oil high in omega-6 fatty acids, soybean oil is highly processed and chemical-extracted.
Corn Oil: Also high in omega-6s, corn oil is heavily processed using chemicals like hexane.
Refined Sunflower Oil: The regular, refined version contains excessive omega-6s and becomes toxic when heated above its smoke point, forming harmful compounds.
Cottonseed Oil: Often derived from a heavily pesticide-treated, non-food crop, cottonseed oil is heavily processed and can contain natural toxins.

The Dangers of Reheating Oil

Another risk factor is the practice of repeatedly reheating oil, especially with deep fryers used in restaurants. When oil is reheated, it breaks down and produces toxic substances, including trans fats, aldehydes, and free radicals, which are associated with inflammation and heart disease.

How to Identify and Avoid Unhealthy Oils

Avoiding unhealthy oils starts with being a diligent label reader. The ban on partially hydrogenated oils helps, but small amounts may still be present.

Common Sources of Hidden Trans Fats

Baked goods: Many cakes, cookies, and pie crusts contain shortening made with partially hydrogenated vegetable oil.
Snacks: Some microwave popcorn, chips, and crackers use trans fat for flavor or texture.
Fried foods: French fries, doughnuts, and fried chicken from fast food and restaurants can contain trans fat from repeated use of oil.
Margarine and Creamer: Stick margarine and non-dairy coffee creamers often contain partially hydrogenated vegetable oils.

The Healthier Cooking Oil Alternatives

Switching to healthier fats can significantly improve your diet and reduce health risks. The healthiest options are typically liquid and plant-based, rich in monounsaturated or polyunsaturated fats.


Comparison of Healthy vs. Unhealthy Oils	Feature	Partially Hydrogenated Oil	Highly Refined Vegetable Oils (Soybean, Corn)	Extra Virgin Olive Oil	Avocado Oil
Fat Composition	Industrial trans fats	High Omega-6 polyunsaturated	High monounsaturated fats	High monounsaturated fats
Processing Method	Industrial hydrogenation with high heat and chemicals	High heat, chemical extraction (hexane), bleaching, deodorizing	Cold-pressed, minimal processing	Cold-pressed, minimal processing
Stability	Very stable, but unhealthy	Unstable at high heat; oxidizes easily	Stable at moderate heat	High smoke point, very stable
Health Impact	Raises LDL, lowers HDL, causes inflammation, increases heart disease risk	High omega-6 ratio promotes inflammation; oxidation products form with heat	Lowers LDL, provides antioxidants, reduces inflammation, supports heart health	Lowers LDL, rich in antioxidants, excellent for high-heat cooking

Conclusion: Making a Mindful Choice

The consensus among health organizations and researchers is clear: industrially produced trans fats from partially hydrogenated oils are the unhealthiest fat to consume, with no safe level of intake. While their presence has been reduced in many countries, vigilance is still required when reading food labels, especially for processed and fried foods. By replacing these harmful fats with healthier options like extra virgin olive oil and avocado oil, you can take a significant step towards a more heart-healthy and anti-inflammatory diet. Remember that the type of fat you consume is far more important than the total amount, so choose your oils mindfully to protect your long-term health.

For more information on dietary fats and heart health, you can consult resources like the American Heart Association.

Frequently Asked Questions

The primary reason trans fats are so unhealthy is their harmful effect on cholesterol levels. They raise "bad" LDL cholesterol while simultaneously lowering "good" HDL cholesterol, which significantly increases the risk of heart disease.

You can tell if a product contains partially hydrogenated oil by checking the ingredient list on the food label. You should look for the words "partially hydrogenated oil" followed by the source, such as "partially hydrogenated soybean oil".

No, omega-6 fatty acids are essential for health, but a high intake, especially without a balance of omega-3s, can promote chronic inflammation. The key is a balanced ratio, which is often disturbed by modern diets high in processed foods.

While the FDA ban has drastically reduced the use of partially hydrogenated oils in the US, it doesn't eliminate all risk. Some foods can be labeled "0g trans fat per serving" if they contain less than 0.5 grams, and this can add up over multiple servings. Additionally, the ban may not apply in all countries.

While not as damaging as trans fats, highly refined vegetable oils like soybean and corn oil are still considered poor choices. They are high in omega-6 fatty acids, heavily processed with chemicals, and can become toxic when overheated, promoting inflammation.

Healthier alternatives include extra virgin olive oil, avocado oil, and algae oil. These are rich in beneficial monounsaturated fats and are more stable during cooking.

Yes, reusing cooking oil, especially repeatedly, is bad for your health. The repeated heating causes the oil to break down and produce harmful compounds like aldehydes and trans fats. This is a major concern with fried foods, particularly in restaurants.