Trans Fats: Where They Hide and the Safety Rules
Where trans fat comes from, how the FDA's 2015 ruling and 2018 deadline changed US food, how to read the 0 g label rule, and what pooled studies say about health.
Content last updated . This page has not been medically reviewed.
Trans fat is the one fat that health bodies say has no known benefit. Most of it has been removed from the US food supply, but a little still reaches the table, and the rules about labels have some small print. This guide explains where trans fat comes from, what the FDA did, how to check a package, and what research found.
Read this first
- Artificial trans fat comes from partially hydrogenated oils (PHOs). In 2015 the FDA decided PHOs are no longer "generally recognized as safe", and most uses had to stop by June 18, 2018. [1] [2]
- Small amounts still occur naturally in milk, butter, cheese and meat from ruminant animals (cows, sheep, goats). The FDA's action did not change these. [1]
- A label can say "0 g" and still hold a little. If a serving has under 0.5 g, the label must show 0 g. [3] Check the ingredient list for "partially hydrogenated" oil. [4]
- Health bodies agree on the direction. Trans fat raises LDL cholesterol. [1] WHO says it has no known health benefits and sets a limit of under 1% of energy. [5]
- Evidence is mostly observational. Pooled cohort studies link higher trans fat to more heart disease and death, but these studies show association, not proof. [6]
Where trans fat comes from
| Source | What it is | What the sources say |
|---|---|---|
| Industrial (artificial) trans fat | Made when liquid oil is partly hydrogenated to make it solid or longer-lasting. | The FDA calls PHOs the major source of artificial trans fat. WHO lists margarine, vegetable shortening, fried foods and baked goods such as crackers, biscuits and pies. [1] [5] |
| Ruminant (natural) trans fat | Forms in the stomach of cows, sheep and goats. | Found in their milk, butter, cheese and meat. [1] [5] |
MedlinePlus lists fried and battered foods, shortening and stick margarine, commercially baked cakes, pies and cookies, refrigerated dough, snack, frozen and fast foods, and nondairy creamer as foods that can contain trans fat. [4]
What USDA lists today
USDA FoodData Central (SR Legacy, April 2018) shows trans fat only where it was measured. Where a row says "not listed", USDA has no value, which is not the same as zero. [7]
| Food (USDA item) | Total trans fat, per 100 g | Per tablespoon (USDA weight) |
|---|---|---|
| Butter, salted (173410) | 3.28 g | about 0.5 g (14.2 g) |
| Margarine-like vegetable oil spread, 67 to 70% fat, tub (171431) | 3.27 g | about 0.5 g (14 g) |
| Soybean oil (171411) | 0.53 g | about 0.1 g |
| Canola oil (172336) | 0.40 g | about 0.1 g |
| Flaxseed oil (167702) | 0.09 g | under 0.1 g |
| Coconut oil (171412) | 0.03 g | under 0.1 g |
| Mayonnaise, regular (171009) | 0.19 g | about 0.03 g (13.8 g) |
| Olive oil (171413), lard (171401), palm oil (171015) | not listed | not listed |
Per-tablespoon values are calculated from per-100-g values and the USDA tablespoon weight. [7] Butter's trans fat is the natural kind. [1] The sources we read do not say where the small amounts in the vegetable oils come from, so we do not guess. The spread listed is a tub spread. [7]
What the FDA did, with dates
| Date | Step, as the FDA page describes it |
|---|---|
| January 2006 | Trans fat must be declared on the Nutrition Facts label. [2] |
| November 2013 | FDA makes a preliminary determination about PHOs. [2] |
| June 16, 2015 | Final determination: PHOs are not generally recognized as safe (GRAS). [2] |
| June 18, 2018 | For most uses, the date after which PHOs could not be added to foods. Foods made before that date had until January 1, 2020 to clear distribution. [2] |
| June 18, 2019 and January 1, 2021 | FDA denied a petition for some limited PHO uses; manufacturing had to stop by June 18, 2019, with distribution until January 1, 2021. [2] |
The FDA estimates that removing PHOs prevents thousands of heart attacks and deaths each year. [1] That is the agency's estimate, not a measured count from our reading.
Reading the label
- Trans fat has no % Daily Value. The FDA says experts could not provide a reference value. [8]
- Under 0.5 g per serving is shown as 0 g. The FDA guide states this rule. [3] If you eat several servings, tiny amounts can add up.
- Ingredient list check. The FDA advises looking for "partially hydrogenated" oils. If present, the product may contain small amounts of trans fat even when the label says 0 g. [3] [4]
- MedlinePlus says "0 g" products can still hold some trans fat per serving, and suggests multiplying by servings eaten. [4] That page gave a threshold figure different from the FDA's 0.5 g rule, so we follow the FDA wording.
- Restaurants: MedlinePlus suggests asking which oils are used for frying. [4]
What research found
| Question | Finding | Strength |
|---|---|---|
| Heart disease and death | A pooled analysis of observational studies found total trans fat linked to higher all-cause death (RR 1.34, 95% CI 1.16 to 1.56), coronary heart disease death (1.28) and total coronary heart disease (1.21). Industrial trans fat was linked to coronary heart disease (1.42), ruminant trans fat was not (0.93). [6] | Observational, moderate certainty for heart outcomes |
| Scale of harm worldwide | WHO says industrially produced trans fat is linked to over 278,000 deaths a year, and that high intake raises coronary heart disease risk by 21%. [5] | Estimates, modeled |
| Dose | The Harvard Nutrition Source says each extra 2% of daily calories from trans fat is associated with a 23% higher risk of coronary heart disease. [9] | Observational |
| Blood fats | Trans fat raises LDL and lowers HDL cholesterol. [4] [9] | Reported by health bodies |
| Ruminant trans-palmitoleic acid and diabetes | The pooled analysis found a lower diabetes risk with a ruminant marker (RR 0.58), but this is one observational signal. [6] | Observational, low certainty |
Limits and recommendations
| Body | Statement, as read |
|---|---|
| WHO | Trans fat of any type should be no more than 1% of total energy, about 2.2 g a day on a 2,000-calorie diet. Industrially produced trans fat is not part of a healthy diet. [5] [10] |
| NHS | Adults should have no more than about 5 g of trans fat a day. [11] |
| FDA | Trans fat raises LDL cholesterol, which raises heart disease risk. [1] |
The WHO figure of 2.2 g and the NHS figure of 5 g come from different bodies and different years of advice. They are general population figures, not personal doses. We did not find a trans-fat-specific rule for pregnancy or for children in the sources read; ask your clinician if you have a heart condition.
Related pages
Frequently asked questions
Is trans fat still allowed in US food?
The FDA ruled in 2015 that PHOs are not generally recognized as safe, with most uses ending June 18, 2018. [2] Natural trans fat in dairy and meat is not covered. [1]
Why does my label say 0 g but list partially hydrogenated oil?
Under the FDA rule, under 0.5 g per serving is shown as 0 g. [3] The ingredient list is the better check. [3]
Is the trans fat in butter as harmful as in margarine?
WHO treats both as equally harmful. [5] A pooled observational analysis linked industrial trans fat to heart disease but not ruminant trans fat, though the authors note people usually eat more of the industrial kind. [6] Studies cannot settle this fully.
What is the daily limit?
WHO: under 1% of energy. NHS: about 5 g for adults. [5] [11] These are public guidance, not a prescription for you.
Do cooking oils make trans fat when heated?
In the sources we read, trans fat in oils was discussed as an ingredient, not as a result of home cooking. Proper evidence not found in the sources we read. See smoke points and cooking with oil for what is known about heated oils.
References
- U.S. Food and Drug Administration. Trans fat. Page last updated 04/30/2024. Read 2026-10-24.
- U.S. Food and Drug Administration. Final determination regarding partially hydrogenated oils (removing trans fat). Read 2026-10-24.
- U.S. Food and Drug Administration. Small entity compliance guide: trans fatty acids in nutrition labeling, nutrient content claims, and health claims. Read 2026-10-24.
- MedlinePlus. Facts about trans fats. Read 2026-10-24.
- World Health Organization. Trans fat fact sheet. January 2024. Read 2026-10-24.
- de Souza RJ et al. Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies. BMJ 2015 (abstract read via Europe PMC). Read 2026-10-24.
- U.S. Department of Agriculture. FoodData Central, SR Legacy (April 2018): items 173410, 171431, 171411, 172336, 167702, 171412, 171009, 171413, 171401, 171015. Read 2026-10-24.
- U.S. Food and Drug Administration. How to understand and use the Nutrition Facts label. Read 2026-10-24.
- Harvard T.H. Chan School of Public Health, The Nutrition Source. Types of fat. Read 2026-10-24.
- World Health Organization. Healthy diet fact sheet. Read 2026-10-24.
- NHS. Different fats in food. Read 2026-10-24.