What Kind of Fat Forms as a Result of Hydrogenation?

December 24, 2025 •

4 min read

According to the World Health Organization, trans fat intake accounts for over 278,000 deaths annually worldwide, a large portion of which are industrially produced. This dangerous fat, formed by the process of hydrogenation, was once prevalent in the food supply for its functional benefits, before its detrimental health effects were fully understood.

Quick Summary

The hydrogenation process converts liquid vegetable oils into solid fats by adding hydrogen, which creates artificial trans fats. These fats increase harmful LDL cholesterol and decrease beneficial HDL cholesterol, raising the risk of heart disease and other chronic conditions.

Key Points

Trans Fats Formation: Partial hydrogenation, a process that adds hydrogen to liquid vegetable oils, creates artificial trans fats by changing the chemical structure of the fatty acids.
Structural Difference: Trans fats have a linear chemical structure, unlike the bent shape of natural cis unsaturated fats, which the human body does not recognize or process properly.
Health Impacts: Consuming trans fats is extremely detrimental to heart health, as it significantly raises harmful LDL cholesterol while decreasing beneficial HDL cholesterol.
Cardiovascular Risk: The double-negative effect on cholesterol and increased inflammation from trans fats leads to a higher risk of heart disease, stroke, and type 2 diabetes.
Identifying Sources: Artificial trans fats are found in processed foods that contain “partially hydrogenated oils,” so consumers should check ingredient lists, not just the nutrition facts label.
Regulatory Action: Due to their proven health dangers, artificial trans fats have been largely banned or restricted in the food supply of many countries.
Avoidance Strategies: Avoiding processed and fried foods, checking labels for “partially hydrogenated oils,” and cooking at home with healthier alternatives are effective ways to reduce trans fat intake.

The Chemistry of Hydrogenation and Trans Fats

What is the Hydrogenation Process?

Hydrogenation is a chemical process that was widely adopted by the food industry in the early 20th century. It involves adding hydrogen to liquid vegetable oils, which are typically unsaturated fats. This process, which requires high temperatures and a metal catalyst like nickel, changes the chemical structure of the fat. By breaking some of the carbon-carbon double bonds and replacing them with single bonds, the process turns a liquid oil into a solid or semi-solid fat at room temperature. This was advantageous for manufacturers as it made the oils more stable, less prone to rancidity, and extended the shelf life of food products.

The Formation of Trans Fats

The most significant result of this process, particularly partial hydrogenation, is the formation of trans fats, or trans-fatty acids. During the partial hydrogenation process, some of the remaining unsaturated double bonds undergo a conformational change, isomerizing from a natural 'cis' configuration to an artificial 'trans' configuration. In a cis fat, the hydrogen atoms on the double bond are on the same side, creating a bend in the molecule. In a trans fat, the hydrogen atoms are on opposite sides, giving the molecule a linear shape, similar to a saturated fat.

It is this altered, linear shape that the human body does not recognize or metabolize effectively. While a small amount of trans fats occurs naturally in the meat and dairy products of ruminant animals, the primary concern for human health comes from the industrially produced trans fats created during partial hydrogenation.

The Health Risks Associated with Trans Fats

The health implications of consuming artificial trans fats are significant and well-documented. Numerous studies have shown that they are far worse for cardiovascular health than saturated fats. Their primary negative effect is a dual-impact on cholesterol: they raise the levels of low-density lipoprotein (LDL), or "bad" cholesterol, while simultaneously lowering the levels of high-density lipoprotein (HDL), or "good" cholesterol. This combination significantly increases the risk of heart attacks, stroke, and other cardiovascular diseases. Trans fat consumption also leads to chronic inflammation and is linked to an increased risk of type 2 diabetes.

Due to these severe health risks, many countries, including the United States, have banned or severely restricted the use of partially hydrogenated oils in food production. This has led the food industry to seek alternative fats and manufacturing processes to replace trans fat-laden ingredients.

Comparison of Fat Types

To better understand the issue, here is a comparison of the three main types of dietary fats:


Feature	Unsaturated Fats	Saturated Fats	Trans Fats
Chemical Structure	Contains one or more double bonds; has a bent shape (cis).	Contains only single bonds; saturated with hydrogen; has a straight shape.	Contains one or more double bonds with an altered, straight shape (trans).
Physical State	Liquid at room temperature (e.g., olive oil).	Solid at room temperature (e.g., butter, lard).	Solid or semi-solid at room temperature (e.g., margarine, shortening).
Primary Source	Plants and fish (e.g., olive, canola, nuts, seeds).	Animal products (meat, dairy) and some plants (coconut, palm oil).	Industrially produced via partial hydrogenation of vegetable oils.
Health Impact	Beneficial; reduces LDL cholesterol and supports heart health.	Can raise LDL cholesterol; typically less harmful than trans fats.	Highly detrimental; raises LDL, lowers HDL, and increases inflammation.
Metabolism	Easily metabolized by the body.	Processed by the body, but can contribute to high cholesterol in excess.	Not recognized or metabolized efficiently, leading to accumulation.

How to Identify and Avoid Trans Fats

Even with regulations in place, it is still possible to consume artificial trans fats, especially in processed foods produced before recent bans took effect or in other countries. Consumers should be vigilant when reading nutrition labels and ingredient lists.

Key steps to avoid trans fats:

Check the Ingredient List: Look for the term "partially hydrogenated oil". Even if a product claims to have "0 g trans fat" on its nutrition facts, it can still contain up to 0.5 grams per serving. If there are multiple servings, this can add up significantly.
Be Mindful of Fast Food: Many fast-food restaurants previously relied on partially hydrogenated oils for frying. While most have switched, it is still wise to check nutritional information, which is often available online or upon request.
Choose Whole Foods: Focus on a diet rich in fruits, vegetables, whole grains, and lean proteins. Cooking at home more often gives you full control over the ingredients used. For baking, use butter or unhydrogenated vegetable oils instead of shortening or stick margarine.
Look for Alternatives: The food industry has developed several alternatives to partially hydrogenated oils, such as interesterified fats, which offer similar functional properties without the health risks of trans fats.

Conclusion

The fat that forms as a result of hydrogenation is known as artificial trans fat. This chemical process, which turns liquid vegetable oils into solid fats, unintentionally creates trans-fatty acids with a linear, unnatural chemical structure. Unlike naturally occurring fats, these artificial trans fats have a severely negative impact on health, specifically by raising bad cholesterol and lowering good cholesterol. The subsequent risks of heart disease, stroke, and diabetes have led to widespread regulations and public health campaigns to eliminate them from the food supply. By understanding the science behind hydrogenation and carefully reading food labels, consumers can effectively avoid this harmful fat and make healthier dietary choices.

For more detailed information on the health impacts of fats, you can consult sources like the World Health Organization's page on trans fat.

Frequently Asked Questions

Partial hydrogenation adds hydrogen to some, but not all, of the double bonds in an unsaturated oil, resulting in both saturated fats and trans fats. Full hydrogenation converts all double bonds into single bonds, producing a fully saturated fat that is free of trans fats.

Yes, small amounts of naturally occurring trans fats can be found in the meat and dairy products of ruminant animals like cows and sheep. However, these are not the industrially produced trans fats that are largely considered a health risk.

The hydrogenation process was used to make liquid oils solid or semi-solid, which was desirable for products like margarine and shortening. It also made fats more stable, extending the shelf life of processed and fried foods by making them more resistant to rancidity.

Trans fats are double trouble for cholesterol. They raise the levels of low-density lipoprotein (LDL), the "bad" cholesterol that clogs arteries, and they lower high-density lipoprotein (HDL), the "good" cholesterol that helps remove cholesterol from the body.

While many countries have banned or severely limited artificial trans fats, they may still be present in foods produced before regulations, in imports, or in small amounts (under 0.5g per serving) that food labels can legally round down to zero. Always check the ingredient list for 'partially hydrogenated oil'.

In the past, trans fats were commonly found in stick margarine, vegetable shortening, commercially baked goods (like cookies, crackers, and pies), fried foods (like doughnuts and french fries), and some snack foods.

When consumed, trans fats are not properly metabolized by the body due to their unnatural shape. This leads to an increase in LDL cholesterol, a decrease in HDL cholesterol, and a rise in systemic inflammation, all of which contribute to serious health conditions like heart disease and stroke.