What is Trans Fat?
Trans fat is an artificially produced type of unsaturated fat created by hydrogenating liquid vegetable oils — widely considered the most harmful type of dietary fat due to its effects on LDL cholesterol, HDL cholesterol, and cardiovascular disease risk.
Trans fat is a type of unsaturated dietary fat that has been artificially modified through a process called partial hydrogenation — adding hydrogen atoms to liquid vegetable oil to make it solid or semi-solid at room temperature. Trans fats extend the shelf life and stability of processed foods and provide desirable texture in baked goods and fried foods — but decades of research have established them as the most harmful type of dietary fat, prompting regulatory action in the United States and worldwide.
How Trans Fats Are Created
Natural vegetable oils are liquid at room temperature because their fatty acid chains contain double bonds in a configuration called cis (the hydrogen atoms are on the same side). Partial hydrogenation reshapes some of those bonds into a trans configuration (hydrogen atoms on opposite sides), increasing the melting point and making the fat more solid and shelf-stable.
The result — referred to as partially hydrogenated oil (PHO) — was widely used in:
- Margarine and shortening
- Fried fast food (French fries, fried chicken)
- Packaged baked goods (cookies, crackers, pie crusts)
- Microwave popcorn
- Frozen pizza dough and pastries
Why Trans Fat Is Harmful
Trans fat has a uniquely damaging effect on cardiovascular health because it acts in two directions simultaneously:
- Raises LDL ("bad") cholesterol — Increases arterial plaque formation
- Lowers HDL ("good") cholesterol — Reduces the body's ability to remove LDL from the bloodstream
This double effect makes trans fat significantly more dangerous than saturated fat, which raises LDL but has a more neutral effect on HDL. Research estimates that replacing 2% of calories from trans fat with healthier fats could reduce heart disease risk by 53%.
Additional health concerns linked to trans fat consumption include:
- Increased systemic inflammation
- Insulin resistance and elevated type 2 diabetes risk
- Increased triglyceride levels
The FDA Ban on Partially Hydrogenated Oils
In 2015, the FDA determined that partially hydrogenated oils (PHOs) were no longer "generally recognized as safe" (GRAS) — effectively banning their addition to food products in the United States. The compliance deadline was June 2018, with limited extensions for certain products through January 2020.
The ban was a significant public health victory. Since food manufacturers began reducing trans fat in the early 2000s following mandatory labeling requirements, cardiovascular disease rates linked to industrial trans fat have declined measurably.
Reading Food Labels
The FDA mandates trans fat disclosure on the Nutrition Facts label. However, the rules allow manufacturers to list 0 grams of trans fat if a serving contains less than 0.5 grams — meaning a product labeled "0g trans fat" can still contain trans fat if you eat multiple servings.
To detect hidden trans fat:
- Look for "partially hydrogenated oil" in the ingredients list
- Any product with PHO as an ingredient contains trans fat, even if the label says 0g
Fully hydrogenated oils are different — they produce saturated fats, not trans fats, and are not subject to the same ban.
Natural Occurring Trans Fats
Small amounts of trans fat occur naturally in meat and dairy products from ruminant animals (cows, sheep, goats). These conjugated linoleic acids (CLA) and vaccenic acid behave differently from industrial trans fats and are not associated with the same cardiovascular risks — some research even suggests potential benefits.
When health authorities discuss trans fat as harmful, they are referring specifically to industrial trans fat from partially hydrogenated oils, not naturally occurring ruminant trans fats.