The Chemical Process Behind Hydrogenation
Hydrogenation is a chemical process that transforms liquid unsaturated fats, like vegetable oil, into solid or semi-solid fats. This is achieved by introducing hydrogen gas to the oil in the presence of a metal catalyst, like nickel, under high temperature and pressure. The purpose is to make the oils more stable, increase their shelf life, and give them a desirable texture for food manufacturing. The outcome, however, depends on whether the hydrogenation is partial or full.
Partial Hydrogenation: The Creation of Trans Fats
The fats that result from partial hydrogenation are primarily what the public has come to know as trans fats, or trans-fatty acids. During this process, some, but not all, of the unsaturated carbon-carbon double bonds are converted to single bonds. Critically, some of the remaining double bonds undergo a structural change, flipping from their natural 'cis' configuration to a 'trans' configuration. It is this new, unnatural 'trans' shape that gives these fats their notoriety.
Industrially produced trans fats have been deemed highly detrimental to human health. They raise levels of LDL (“bad”) cholesterol while simultaneously lowering levels of HDL (“good”) cholesterol. This double-edged effect significantly increases the risk of heart disease, stroke, and type 2 diabetes. Given the overwhelming evidence of harm, the U.S. Food and Drug Administration (FDA) made a final determination in 2015 that partially hydrogenated oils are no longer "Generally Recognized as Safe" (GRAS), effectively banning them from most manufactured food production.
Full Hydrogenation: An Alternative Approach
In contrast to partial hydrogenation, full or complete hydrogenation fully saturates all the carbon-carbon double bonds. This process produces a fat that is solid at room temperature and is chemically similar to naturally occurring saturated fats. Unlike partially hydrogenated oils, fully hydrogenated oils do not contain artificial trans fats and are therefore considered a safer alternative. For example, the hydrogenation of soybean oil converts its unsaturated fatty acids into saturated stearic acid, which does not negatively impact cholesterol in the same way as trans fats. Food manufacturers have increasingly turned to fully hydrogenated oils or other naturally saturated oils, like palm oil, to replace PHOs in their products.
Comparison of Partially vs. Fully Hydrogenated Oils
| Feature | Partially Hydrogenated Oils (PHOs) | Fully Hydrogenated Oils |
|---|---|---|
| Hydrogenation Process | Incomplete saturation of double bonds. | Complete saturation of all double bonds. |
| Resulting Fat Type | Contains artificial trans fats. | Does not contain trans fats; is a saturated fat. |
| Melting Point | Semi-solid consistency at room temperature. | Solid consistency at room temperature. |
| Health Impact | Raises LDL, lowers HDL, increases risk of heart disease. | Does not negatively impact cholesterol like trans fat; consumption of saturated fats should still be monitored. |
| Regulatory Status | FDA banned as a food additive due to safety concerns. | Permitted in food manufacturing. |
Where You Might Find Hydrogenated Fats
Despite the FDA ban, residual amounts of trans fat may still exist in some older products or through natural sources. Consumers should always be vigilant when reading food labels. Key words to look for include "partially hydrogenated oil" in the ingredients list. Trans fats from PHOs were traditionally found in a variety of processed and packaged foods.
Foods that traditionally contained PHOs:
- Commercial baked goods (cookies, cakes, pies, crackers)
- Fried foods (doughnuts, french fries)
- Solid fats (vegetable shortening, stick margarine)
- Packaged snacks (microwave popcorn)
- Refrigerated doughs
It is important to remember that some trans fats occur naturally in small amounts in meat and dairy from ruminant animals. While artificial trans fats are the primary concern, a balanced perspective on all fat intake is important for overall health. Opting for whole, unprocessed foods and liquid vegetable oils like olive oil can help limit consumption of all potentially harmful fats. For a healthy and informed diet, understanding the difference between partially and fully hydrogenated fats is crucial. The FDA provides detailed information on the ban of partially hydrogenated oils for interested readers. [https://www.fda.gov/food/food-additives-petitions/trans-fat]
Conclusion
In summary, the fats that arise from the partial process of hydrogenation are called artificial trans fats. These manufactured fats are distinctly different from typical saturated fats and pose significant health risks, leading to their ban by the FDA in most food products. Fully hydrogenated fats, created through complete saturation, are a safer alternative but are still saturated fats and should be consumed in moderation. By understanding the science and reading labels, consumers can make healthier dietary choices and actively avoid artificial trans fats. For better health, replace processed foods containing hydrogenated oils with heart-healthy alternatives like fruits, vegetables, and whole grains.
