Why is poop green after eating fast food?

Experiencing green poop after eating fast food is usually common and often harmless. It typically happens for one of two main reasons:

• Artificial food dyes: Some fast foods, drinks, and desserts contain green, blue, or black dyes that can pass through digestion and tint stool green.
• Fast digestion (bile): Greasy or very fatty foods can sometimes move stool through the intestines more quickly. Bile starts out green, and if it doesn’t have enough time to be broken down into brown pigments, stool can look green.

In many cases, the color change goes back to normal once the food has fully passed through your system, which is often within a day or two, though timing can vary from person to person.

Staying hydrated can help support normal digestion.

If the green stool lasts more than a few days, or comes with severe abdominal pain, persistent diarrhea, fever, or blood, get medical advice.