What Happens When I Eat Trans Fat?

Donuts are often high in trans fats.
Those donuts may have trans fats. Jordan Siemens/The Image Bank/Getty Images

QuestionWhat happens to trans fat after it's ingested?  Does the body turn it into something? Or does it simply accumulate? Does it ever get eliminated from the body?  I'm asking because I'm not sure if we should be concerned with sometimes eating something that contains artificial trans fat by accident, and with all the trans fats that we ate before it was known to be harmful. 

Answer: Trans fats are digested and absorbed like all other fats.

Basically, the fats you eat are broken down in the small intestine, then the individual fatty acids (trans, saturated, poly- and monounsaturated) are absorbed across the small intestinal walls. 

From there, some fatty acids go straight to the liver via the portal vein, while others -- including the trans fatty acids -- are packaged up into chylomicrons and lipoproteins (cholesterol) and enter the bloodstream through the lymphatic system. They're transported throughout the body -- and if they're not used up, they're stored as fat, just like other fatty acids.

So, the more trans fat you consume, the more trans fatty acids you'll have in your body fat. When you use the trans fatty acids as energy, it's catabolized to carbon dioxide and water and removed from the body -- just like other fats.

The problem with trans fats is that they can increase your LDL cholesterol (the bad kind) and reduce HDL cholesterol (the good kind).

This increases your risk for cardiovascular disease and diabetes.

How Much Trans Fat is Okay?

The American Heart Association recommends you take in less than 1 percent of your daily calories come from trans fats. So, if you typically consume 2,000 calories per day, then only 20 calories can come from trans fats.

That's not much -- only about 2 grams.

The American Heart Association includes naturally-occurring trans fatty acids in that daily 2 grams. It's not clear that naturally occurring trans fats called conjugated linoleic acid are harmful -- they might even be beneficial -- but since they're found in meats and dairy products, they're accompanied by saturated fats that also raise your risk for cardiovascular disease. So it's best to avoid them.

Finding Trans Fats in Foods

Heres' where Nutrition Facts labels are your best friends. The amount of trans fats must be disclosed on the package label, as long as there are more than 0.5 grams per serving. Since the downsides of trans fats are well known at this point, there are fewer and fewer foods that contain them.

But what if you're eating food prepared at a restaurant or a friend's house --  how do you know if you're eating trans fats?

Typically, you still might find trans fats in cheaper commercial varieties of pastries, pie crusts, pizza crust, cookies, and crackers, and some forms of stick margarine.

 You can always ask what ingredients are used to make the dish you want to eat or avoid the foods that you think might contain them.

There's no need to panic if you accidentally consume some trans fat at a meal -- just go back to your regular healthy diet.  There's not much you can do about the trans fats you ate in the past either, but if you have other risk factors for heart disease, then make an appointment to see your healthcare provider, who can assess your overall risk and suggest appropriate dietary changes.


American Heart Association, "The Dish: Artificial or Natural? Taking in Trans Fats." Accessed May 6, 2016. http://www.heart.org/HEARTORG/GettingHealthy/FatsAndOils/TheDishwithDrEckel/The-Dish-Artificial-or-Natural-Taking-in-Trans-Fats_UCM_304897_Article.jsp.

American Heart Association, "Trans Fat." Accessed May 6, 2016. http://www.heart.org/HEARTORG/GettingHealthy/FatsAndOils/Fats101/Trans-Fats_UCM_301120_Article.jsp.

Gropper SS, Smith JL, Groff JL. "Advanced Nutrition and Human Metabolism." Sixth Edition. Belmont, CA. Wadsworth Publishing Company, 2013. Accessed May 6, 2016.

Smolin LA, Grosvenor, MB. "Nutrition: Science and Applications." Third Edition. Wiley Publishing Company, 2013. Accessed May 6, 2016.

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