Fatty acids, total trans

Trans fat is a type of dietary fat formed when liquid vegetable oils are chemically hardened, or that occurs naturally in small amounts in beef, lamb, and dairy. Of all dietary fats, it is the one health authorities single out most strongly, because it both raises LDL ("bad") cholesterol and lowers HDL ("good") cholesterol — a combination linked to increased heart disease and stroke risk that has led U.S. regulators to remove its main industrial source from the food supply.

What is trans fat

Trans fats get their name from the geometry of a chemical bond in the fatty acid chain. Most naturally occurring unsaturated fats have a "cis" bond configuration; trans fats have a "trans" configuration instead, which straightens the molecule and makes it behave more like a saturated fat — solid and shelf-stable — even though it's technically unsaturated. Industrial, or artificial, trans fat is created by partially hydrogenating liquid vegetable oils — bubbling hydrogen gas through the oil with a catalyst — to make partially hydrogenated oils (PHOs), which were widely used in shortening, margarine, and fried and baked goods because they extend shelf life and add texture. Per MedlinePlus, PHOs are made when "liquid oils are turned into solid fats, like shortening or margarine," and the ingredient-list phrase to watch for is "partially hydrogenated." A smaller amount of trans fat also occurs naturally, produced by bacteria in the stomachs of ruminant animals, which is why trace amounts turn up naturally in beef, lamb, and dairy products such as cheese and butter even without any industrial processing.

Health effects of trans fat

As with saturated fat, there is no health benefit associated with consuming trans fat — every documented effect runs toward increased risk. MedlinePlus states that trans fats raise LDL cholesterol while also lowering HDL cholesterol, a combination that "can cause cholesterol to build up in your arteries" and increases the risk of heart disease and stroke; the same page also links high trans fat intake to increased diabetes risk through its effect on body weight, since trans fats carry the standard 9 calories per gram of any dietary fat. Harvard T.H. Chan School of Public Health, The Nutrition Source describes trans fat as creating inflammation in addition to its cholesterol effects, and cites a dose-response relationship in which each additional 2% of daily calories from trans fat is associated with a 23% higher risk of coronary heart disease.

How much you need

There is no Recommended Dietary Allowance, Adequate Intake, or Tolerable Upper Intake Level for trans fat — the DB's nutrient_rda table has no row for it, and none should exist, because trans fat serves no required function in the body. The guidance here is a limit, not a target, and it's the strictest of any dietary fat: MedlinePlus states plainly, "Your body does not need trans fat. You should avoid it or eat as little as possible." That is a qualitative "as low as possible" standard rather than a specific gram or percent-of-calories ceiling, which reflects the fact that no beneficial level of intake has been identified.

Signs of low and high intake

There is no deficiency associated with low or zero trans fat intake — trans fat performs no essential biological function, so eating none of it carries no documented nutritional downside. On the high-intake side, the concern is the same cardiovascular pattern described above rather than an acute toxicity: sustained higher trans fat intake is associated with elevated LDL cholesterol, reduced HDL cholesterol, arterial plaque buildup, and higher long-term risk of heart disease, stroke, and type 2 diabetes, per MedlinePlus. These are cumulative, dietary-pattern effects, not symptoms that appear from a single exposure.

Warnings & interactions

No drug or supplement interactions are documented for dietary trans fat — as with saturated fat, the relevant caution is dietary rather than pharmacological. The clearest regulatory action on this nutrient came from the U.S. Food and Drug Administration, which in 2015 determined that partially hydrogenated oils are no longer "Generally Recognized as Safe" for use in food; manufacturers were barred from adding PHOs to most foods after June 18, 2018, with the FDA stating that removing PHOs from processed foods "could prevent thousands of heart attacks and deaths each year." The FDA also noted that trans fat has not fully disappeared from the food supply, since it still occurs naturally in small amounts in meat and dairy. Because no RDA/AI/UL exists, there is no defined "above-UL" threshold to report — the standing caution is simply to keep intake as low as possible, per the guidance in the section above, and it applies to the general population rather than a specific at-risk subgroup.

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