Trans fat
Trans fatty acids are unsaturated fats with at least one trans-configured double bond. Industrial trans fat, produced by partial hydrogenation of vegetable oil, raises LDL and lowers HDL simultaneously and is estimated by the WHO to have caused 500,000 premature deaths per year before regulation. The WHO REPLACE initiative targets global elimination of industrial trans fat.
What is trans fat?
A trans fatty acid is an unsaturated fatty acid whose double bond is in the trans stereochemical configuration rather than the cis form found in most natural fats. The geometry lets the chain pack more like a saturated fat — solid at room temperature — but the metabolic effect is worse than saturated fat. The vast majority of trans fat in the industrial food supply came from partial hydrogenation of vegetable oil, a process introduced by Procter & Gamble in 1911 (Crisco) to give liquid seed oils the mouthfeel and shelf life of lard.
Why it is uniquely harmful
Mensink and colleagues (New England Journal of Medicine 1990;323:439–445) showed that industrial trans fat raises LDL cholesterol comparably to saturated fat but also lowers HDL. Subsequent trials confirmed the double effect on the LDL:HDL ratio (Ascherio, NEJM 1999;340:1994–1998). Mozaffarian, Katan, Ascherio, Stampfer, and Willett summarised the evidence base in their landmark NEJM review (2006;354:1601– 1613): each 2% of energy from industrial trans fat raises coronary heart disease incidence by 23%.
Regulatory timeline
| Year | Jurisdiction | Action |
|---|---|---|
| 2004 | Denmark | First national cap: 2% of fat in any food |
| 2006 | US | Nutrition Facts label must declare trans fat grams |
| 2007 | New York City | Restaurants restricted from serving PHO-based food |
| 2015 → 2018 | US FDA | GRAS status revoked for partially hydrogenated oils |
| 2018 | WHO | REPLACE action package — global elimination by 2023 target |
| 2019 → 2021 | EU | 2 g industrial trans fat per 100 g fat cap |
| 2024 | WHO progress report | ~60 countries with best-practice policy; ~5B people still uncovered |
Where residual trans fat still appears
- Some imported bakery, biscuits, and pastry from jurisdictions without restrictions.
- US products where per-serving grams round down to zero (labels can declare "0 g" up to 0.49 g).
- Deep-fry systems in restaurants that have not switched from PHO shortenings.
- Older-formulation coffee creamers and microwave popcorn (mostly phased out post-2018).
How NakedCalorie treats trans fat
Trans-fat grams are shown on the nutrient panel. The presence of "partially hydrogenated" or equivalent language on the ingredient list is a direct flag on the food-quality score, independent of the declared grams — the label-rounding loophole is the reason the ingredient check exists. See hydrogenated oils for the ingredient-level article, and dietary fats for the parent overview.
Frequently asked questions
- Where does trans fat come from?
- Two sources. Industrial trans fat is produced by partially hydrogenating vegetable oil to solidify it — the classic ingredient in shortening, older margarine, and long-shelf-life bakery. Ruminant trans fat occurs naturally in small amounts in dairy and beef from bacterial biohydrogenation in the cow's rumen.
- Are ruminant trans fats also harmful?
- At typical dietary intakes (<0.5% of energy) the evidence is neutral to mildly beneficial (Gebauer, Advances in Nutrition 2011;2:332–354). The harm signal is specific to industrial partial hydrogenation, which produces different isomer profiles at higher exposure.
- Isn't industrial trans fat already banned?
- In much of the world, yes. Denmark led in 2004; the US FDA revoked GRAS status for partially hydrogenated oils in 2015 (effective 2018); the EU set a 2% cap in 2019 (in force 2021). About 60 countries had binding limits as of 2024, but 5 billion people still live in countries without best-practice policy (WHO 2024 progress report).
- How do I spot residual trans fat on a label?
- In the US, products can declare '0 g trans fat' if the amount is under 0.5 g per serving. The tell is 'partially hydrogenated' on the ingredient list — read the ingredients, not the highlight box. Fully hydrogenated oil is different (essentially all saturated fat) and does not raise the same concern.
- What did trans-fat regulation actually achieve?
- Restrepo and Rieger (Journal of Health Economics 2016;45:185–194) showed a 4.5% drop in CHD mortality in New York counties that restricted trans fat in restaurants, versus counties that did not. Denmark's national ban was followed by measurable declines in CVD mortality (Restrepo & Rieger 2016; Downs, PLOS Medicine 2013).
Written by NakedCalorie editorial team.
Medically reviewed by Pending registered dietitian review — last reviewed July 15, 2026.
Educational information only, based on peer-reviewed literature and regulatory sources. Not medical advice.
Related in the knowledge base
- MacronutrientsDietary fats
- MacronutrientsSaturated vs unsaturated fat
- IngredientsHydrogenated and partially hydrogenated oils