What is the problem with partially hydrogenated oil? A deep dive into trans fats

October 7, 2025 •

4 min read

According to the World Health Organization, more than 278,000 deaths annually are attributed to the consumption of industrially produced trans fats, which are primarily derived from partially hydrogenated oil (PHO). Though PHOs were once prized for their stability and long shelf life in processed foods, the health problems they cause led the FDA to ban them from the U.S. food supply. Understanding the specific dangers of this once-common ingredient is crucial for making informed dietary choices.

Quick Summary

Partially hydrogenated oil (PHO) is the major source of artificial trans fats, known to raise harmful LDL cholesterol while lowering beneficial HDL cholesterol. Its consumption is linked to severe health issues like heart disease, chronic inflammation, and an increased risk of stroke. Regulatory actions, such as the FDA ban, reflect the significant public health risk posed by PHOs.

Key Points

Source of Artificial Trans Fat: Partially hydrogenated oil (PHO) is the major industrial source of trans fat, a synthetic fat produced during the manufacturing process.
Increases Bad Cholesterol: Trans fat raises LDL ('bad') cholesterol levels, contributing to plaque buildup in arteries.
Lowers Good Cholesterol: Simultaneously, it lowers HDL ('good') cholesterol, which is responsible for removing excess cholesterol from the bloodstream.
Promotes Chronic Inflammation: It triggers chronic inflammation, a risk factor for heart disease, diabetes, and other chronic conditions.
Increases Disease Risk: This combination of effects significantly elevates the risk of heart disease, stroke, and type 2 diabetes.
Largely Banned in the U.S.: The FDA determined in 2015 that PHOs are not safe to eat, leading to a ban that went into full effect in 2021.
Requires Continued Vigilance: Due to labeling loopholes, some processed foods may still contain trace amounts of trans fat, necessitating careful label-reading.
Healthier Alternatives Exist: Healthier alternatives to PHO include vegetable oils like olive and canola, as well as palm oil and fully hydrogenated options that contain no trans fats.

What exactly is partially hydrogenated oil?

Partially hydrogenated oil (PHO) is created through a chemical process called hydrogenation, which involves adding hydrogen to liquid vegetable oil. This process solidifies the oil, making it more stable and resistant to spoilage, which is why it became a popular ingredient in processed and packaged foods. However, the 'partial' nature of this process is the key to the problem, as it rearranges the chemical structure of the fatty acids, creating a particularly harmful type of fat known as artificial trans fat. This differs significantly from fully hydrogenated oil, which contains saturated fat and little to no trans fat, or the small amounts of naturally occurring trans fat found in some meat and dairy products.

The grave health problems with partially hydrogenated oil

The primary danger of PHOs stems directly from the artificial trans fats they contain. These fats have been unequivocally linked to a host of serious health complications, with the World Health Organization (WHO) identifying them as a leading contributor to cardiovascular disease mortality. While the FDA has largely phased them out of the U.S. food supply, understanding their impact remains vital for consumer awareness globally and for managing overall dietary fat intake.

Cardiovascular disease

Trans fats are often called the worst type of fat for your heart health because they harm your cardiovascular system in two critical ways. First, they increase levels of low-density lipoprotein (LDL) cholesterol, the "bad" cholesterol that contributes to plaque buildup in the arteries. Second, they simultaneously decrease levels of high-density lipoprotein (HDL) cholesterol, the "good" cholesterol that helps remove cholesterol from the arteries. This dual effect of raising bad cholesterol and lowering good cholesterol is a direct pathway to increased risk of heart attacks and stroke.

Chronic inflammation and related conditions

Beyond cholesterol, artificial trans fats are known to trigger and exacerbate chronic inflammation throughout the body. While acute inflammation is a healthy immune response, long-term, low-grade inflammation is a known risk factor for a wide range of chronic diseases, including heart disease, diabetes, and certain cancers. The inflammatory effects of trans fats can damage arterial cells and disrupt the normal function of blood vessels, further contributing to heart disease.

Insulin resistance and type 2 diabetes

Studies have also linked higher trans fat intake with an increased risk of insulin resistance, a precursor to type 2 diabetes. This happens because trans fats can impair your body's ability to use insulin effectively, leading to elevated blood sugar levels. For individuals already predisposed to metabolic issues, the presence of trans fats can intensify these problems.

The comparison: Partially hydrogenated vs. alternative fats


Feature	Partially Hydrogenated Oil (PHO)	Fully Hydrogenated Oil	Unsaturated Fats (e.g., olive, canola)	Saturated Fats (e.g., butter, lard)
Trans Fat Content	High (Primary source of artificial trans fat)	Very low or zero	Zero	Very low (naturally occurring)
Health Impact	Significantly increases risk of heart disease, inflammation, and diabetes	Better than PHO, but high intake can still be linked to health issues	Promotes heart health and lowers bad cholesterol when used in place of trans fat	High intake may raise LDL cholesterol; impact depends on source
Food Uses	Previously used in many fried and processed baked goods, shortening, and margarine	Creates firmer products; alternatives are now preferred	Cooking, baking, and salad dressings	Used in baking, cooking, and spreads; once widely replaced by PHOs
Regulatory Status	FDA banned as no longer considered Generally Recognized As Safe (GRAS)	Allowed, but foods containing them are often processed and may be high in saturated fat	Unregulated in terms of hydrogenation; healthy fat source	Allowed; intake should be limited according to dietary guidelines

How to avoid partially hydrogenated oil

Despite the FDA ban, it's still essential to be vigilant about food labels. Some products with very small amounts of trans fat (less than 0.5 grams per serving) can still be labeled as containing "0 grams trans fat," so checking the ingredients list is the most reliable method. Look for the words "partially hydrogenated oil" or "shortening" in the list of ingredients.

Here are actionable tips to reduce your intake:

Choose whole foods: Focus on cooking with fresh fruits, vegetables, whole grains, nuts, and seeds instead of relying on packaged and processed products.
Read labels carefully: Even if a package claims "0g trans fat," check the ingredients list for the words "partially hydrogenated oil". Hidden trans fats can add up quickly if you consume multiple servings.
Cook at home more often: Many restaurants, particularly fast-food establishments, used PHOs for frying and baking. Cooking at home gives you full control over the oils you use.
Choose healthier alternatives: When cooking or baking, use liquid vegetable oils like olive, canola, or sunflower oil instead of solid shortenings or margarines that may contain hidden trans fats.
Opt for fresh and minimally processed snacks: Instead of prepackaged snacks like crackers, cookies, and microwave popcorn, choose whole-food options such as nuts, fruits, and yogurt.

Conclusion: A public health success story with ongoing vigilance

The story of partially hydrogenated oil is a significant public health success, with regulatory bodies taking action to remove a dangerous ingredient from the food supply. However, it also serves as a crucial reminder of the importance of nutritional literacy. While the ban has dramatically reduced the average intake of artificial trans fats, they may still be present in trace amounts in some processed foods. The best strategy for a heart-healthy diet is to prioritize whole, unprocessed foods and to remain a diligent label-reader. Replacing PHOs with healthier, unsaturated fats is a simple yet powerful step toward protecting your long-term cardiovascular health. For more information on heart-healthy diets, consult resources like the American Heart Association.

Frequently Asked Questions

Partially hydrogenated oil is created through a process that leaves some double bonds in the fat molecule, which produces artificial trans fats. Fully hydrogenated oil, by contrast, has all its double bonds saturated with hydrogen, creating a solid fat with virtually no trans fats.

No, trans fat is a type of fat, while partially hydrogenated oil is the specific ingredient that is the primary source of artificial trans fats in processed foods. The process of partial hydrogenation creates trans fats as a byproduct.

The main health concerns include a significantly increased risk of cardiovascular disease by raising LDL (bad) cholesterol and lowering HDL (good) cholesterol. Trans fats also promote chronic inflammation and are linked to insulin resistance and type 2 diabetes.

In the United States, the FDA has largely phased out the use of PHOs, with a ban effective since 2021. However, some older products or trace amounts may still be found, and international regulations may differ.

You should check the ingredient list for the phrase "partially hydrogenated oil". Even if the Nutrition Facts panel says "0g trans fat," small amounts (under 0.5 grams per serving) may still be present.

Healthy alternatives include liquid vegetable oils that are naturally low in saturated fats and high in monounsaturated or polyunsaturated fats, such as olive, canola, and sunflower oil. Using liquid oils instead of solid fats like shortening is generally a healthier choice.

While natural trans fats found in meat and dairy occur in smaller amounts than industrial trans fats, both types have been shown to have negative health effects. However, the primary health concern and the focus of regulatory bans is the industrially produced trans fat from PHOs.