IIRC, trans fats were banned in the US. I don't think it works be legal for them to contain them anymore.

Partially hydrogenated oils, a major source of artificial trans fats, have been banned. Not all trans fats have been banned and they are not all artificial, they are also naturally occurring.

Jiffy corn muffin mix doesn't contain partially hydrogenated vegetable oils and contains zero grams of trans fats per serving (I have seen it claimed that products may have less than 0.5 grams per serving and round down to zero).

https://www.fda.gov/food/ingredientspackaginglabeling/foodad...

https://en.wikipedia.org/wiki/Trans_fat

https://site.jiffymix.com/product/

I believe it did last time I looked at a box of it that I had in my kitchen. Maybe they removed them a little while back?

That's very possible. However, looking at 3rd party site that lists ingredients and nutritional information, Jiffy Corn Muffin Mix did not contain partially hydrogenated vegetable oils and listed zero grams of trans fats [0]. The site doesn't list when the information was added but the comment history goes back to 2011.

They do also have a page for a Jiffy Baking Mix (no corn, sounds similar to Bisquick) that did contain partially hydrogenated vegetable oils, enough for one gram trans fats per serving.

[0] https://www.fooducate.com/app#!page=product&id=43DBDE62-E10F...

[1] https://www.fooducate.com/app#!page=product&id=43BFE144-E10F...