There's some good news and some not so good news. Yes, McDonald's french fries are made with real potatoes. However, they also contain a whole lot of extras.

See also: Watch how the McRib is really made

The revelations come from the fast-food chain's new video, the latest in a series called "Our food. Your questions" in which Mythbusters co-host Grant Imahara tries to debunk rumors about their food.

In the clip, Imahara, "reverse engineers" the process of french fry production, to trace the food right back to the source: a potato that comes straight from the ground.

And it turns out they do use real potatoes, a mix including Russet Burbanks and Umatilla Russets to be precise. But then, as revealed in a companion video, they add a few extra ingredients.

Image: Eugene Hoshiko/Associated Press

Dextrose, a natural sugar, to keep the color consistent and sodium acid pyrophosphate, to keep the fries from graying, for starters. Natural beef flavor, hydrogenated soybean oil, dimethylpolysiloxane and TBHQ also join the party.

Together they add up to 337 calories and 17 grams of fat for a medium serving.

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