Trans fats: the most harmful type of fat
Nutrition
Key points
- +2% of calories from trans fat was linked to +23% risk of coronary heart disease.
- Trans fats raise "bad" LDL cholesterol and lower "good" HDL cholesterol.
- Look for "partially hydrogenated oil" in the ingredient list.
- There is no safe level of industrial trans fat.
Why trans fats are harmful
Partial hydrogenation turns liquid oils into solid fats that extend shelf life, which is why trans fats were once common in stick margarine, shortening, packaged baked goods, microwave popcorn and fried fast food.
A review in the New England Journal of Medicine found that trans fats are worse for the heart than any other fat. They raise LDL cholesterol, lower HDL cholesterol and promote inflammation. A 2% increase in calories from trans fat was linked to a 23% higher risk of coronary heart disease (Mozaffarian et al., 2006). The American Heart Association recommends eliminating industrial trans fats entirely (Sacks et al., 2017).
The U.S. ban
In 2015, the FDA determined that partially hydrogenated oils are no longer “generally recognized as safe”, and manufacturers had until 2018 to 2020 to remove them. The WHO is calling for all countries to eliminate industrial trans fats.
How to avoid them
- Read the ingredient list: avoid “partially hydrogenated” oils, especially in imported products.
- Remember that “0 g trans fat” on a label can mean up to 0.5 g per serving.
- Limit deep-fried restaurant food and packaged pastries.
- Cook with liquid vegetable oils.
Frequently asked questions
Are trans fats still in U.S. food?
Since the FDA’s determination took full effect, partially hydrogenated oils can no longer be added to foods in the U.S. Small amounts occur naturally in meat and dairy, and products labeled "0 g trans fat" can contain up to 0.5 g per serving.
What about margarine?
Most U.S. margarines and spreads today are made without partially hydrogenated oils. Check the ingredient list.
Sources
- Mozaffarian et al. (2006). Trans Fatty Acids and Cardiovascular Disease. New England Journal of Medicine 354(15):1601-1613. doi:10.1056/NEJMra054035
- Sacks et al. (2017). Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association. Circulation 136(3). doi:10.1161/CIR.0000000000000510
- Afshin et al. (2019). Health effects of dietary risks in 195 countries, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. The Lancet 393(10184):1958-1972. doi:10.1016/S0140-6736(19)30041-8
Keep reading
Nutrition Dietary fats: olive oil, butter and your heart
Why replacing saturated fat with vegetable oils lowers heart disease risk according to the American Heart Association, and what U.S. cohorts found about olive oil.
Nutrition · Myth or factMyth or fact: fruit is bad for you because of its sugar
Is fruit sugar harmful? What large U.S. cohort studies show about whole fruit, fruit juice and type 2 diabetes risk.
Nutrition Milk and dairy: how much do adults really need?
What a New England Journal of Medicine review says about the three-cups-a-day advice, dairy and fractures, and how to get calcium if you skip dairy.
Nutrition tools
MEDAS: how Mediterranean is your diet?
The PREDIMED trial screener (13 questions; we deliberately removed the wine item).
QuizHow much fiber do you eat? Calculator
A rough estimate of your daily fiber based on your habits.
QuizToo much sodium? Self-check
The habits that affect your sodium intake the most.
PDF · PlannerWeekly meal planner using the plate method
A 7-day planner with plate-method prompts and space for your grocery list.
PDF · ChecklistHealthy grocery list
A grocery checklist by food group, with blank lines for your own items.
PDF · Cheat sheetCheat sheet: read a Nutrition Facts label in one minute
A wallet or fridge card with % Daily Value rules and what to look for.