What is Hydrogenation and How Does it Work?
Hydrogenation is a chemical process used in food manufacturing that involves adding hydrogen to liquid vegetable oils. In their natural state, most vegetable oils are unsaturated fats, which means their chemical structure contains double bonds. This molecular structure is what keeps them liquid at room temperature. The hydrogenation process uses a metal catalyst, like nickel, and high pressure and temperature to force hydrogen atoms to bond with the oil's fatty acid chains.
There are two main types of hydrogenation: partial and complete.
- Partial hydrogenation: This process only adds hydrogen to some of the double bonds. This is the process that creates trans fats. The remaining double bonds are altered from a natural 'cis' configuration (where hydrogen atoms are on the same side) to an unnatural 'trans' configuration (where hydrogen atoms are on opposite sides), resulting in a straighter, more solid fat molecule.
- Complete hydrogenation: This process adds hydrogen to all of the double bonds, fully saturating the oil. This produces a fat that is solid and waxy, and virtually free of trans fats. However, it is high in saturated fat and typically blended with unhydrogenated oils to achieve a desirable consistency.
The industrial motivation behind hydrogenation is multifaceted. By converting liquid oil into solid or semi-solid fat, manufacturers can create products with specific textures, such as margarine and shortening. Furthermore, the process increases the fat's stability and shelf life, protecting against oxidation and spoilage.
The Harmful Health Effects of Trans Fat
Trans fats are considered the unhealthiest type of fat because of their significant negative impact on cardiovascular health. Unlike other fats, trans fats simultaneously raise low-density lipoprotein (LDL) or "bad" cholesterol and lower high-density lipoprotein (HDL) or "good" cholesterol. This dual effect is particularly damaging, as it increases the risk of heart attacks and coronary heart disease.
Where Trans Fats are Found
Due to widespread health warnings and regulatory actions, many companies have reduced or eliminated trans fats. However, they can still be found in some products.
- Processed baked goods: Crackers, cookies, and pastries often used partially hydrogenated oils for texture and shelf life.
- Fried foods: Many restaurants used partially hydrogenated oil for deep-frying because of its stability.
- Margarine and shortenings: Early versions of these products were a major source of trans fat. While most have been reformulated, checking the label is still important.
- Microwave popcorn: Some microwave popcorn varieties historically contained trans fat in their butter-flavored formulations.
How Hydrogenation Differs from Natural Fats
To understand why industrial hydrogenation produces an unhealthy fat, it's helpful to compare it with other fat types.
| Feature | Trans Fat (Hydrogenated) | Saturated Fat (Natural) | Unsaturated Fat (Natural) |
|---|---|---|---|
| Molecular Shape | Straightened (Trans) | Straight | Kinked (Cis) |
| State at Room Temp | Solid or semi-solid | Solid | Liquid |
| Chemical Stability | Highly stable | Stable | Less stable |
| Primary Sources | Processed foods, shortening, margarine | Animal products, coconut oil, palm oil | Plant-based oils, seeds, nuts |
| Cholesterol Impact | Increases LDL, decreases HDL | Increases both LDL and HDL | Decreases LDL, increases HDL |
| Health Impact | Significantly raises heart disease risk | Moderate risk, best consumed in moderation | Generally considered healthy, heart-protective |
Regulation and Replacement of Trans Fat
Awareness of the health risks associated with trans fat has led to significant global regulatory action. Countries and health organizations, like the World Health Organization (WHO), have pushed for the elimination of industrially produced trans fats from the food supply. The U.S. Food and Drug Administration (FDA) made a final determination in 2015 that partially hydrogenated oils (PHOs) are no longer 'generally recognized as safe' (GRAS) for use in food products.
As a result, the food industry has sought healthier alternatives to replace partially hydrogenated oils. These replacements include: interesterified fats, which rearrange fatty acids on a glycerol backbone without creating trans fats; blending liquid oils with harder, naturally saturated fats; and using advanced fractionation techniques.
Conclusion
When hydrogen is added to vegetable oil through the industrial process of partial hydrogenation, the resulting fat is known as trans fat. This modification increases the oil's stability and solidity, but also creates a highly detrimental fat for human health. Trans fats uniquely raise bad cholesterol while lowering good cholesterol, significantly increasing cardiovascular disease risk. Due to mounting health concerns and regulatory changes, the food industry is now moving away from partially hydrogenated oils toward healthier alternatives to achieve desired food textures and shelf life. Consumers can protect their health by checking nutrition labels for "partially hydrogenated oil" and opting for foods made with natural, unhydrogenated oils.
Center for Science in the Public Interest: Trans Fat (Partially hydrogenated vegetable oil)
