Dark green poop is almost always caused by something you ate, a supplement you’re taking, or food moving through your digestive system faster than usual. It’s rarely a sign of something serious on its own, but the specific shade and any accompanying symptoms can help you figure out what’s going on.
How Poop Gets Its Color
Your liver produces bile, a bright green fluid that helps you digest fats. As bile travels through your intestines, bacteria break it down and chemically transform it from green to yellow to brown. That’s why healthy stool is typically some shade of brown: it means bile had enough time to be fully processed during digestion.
When food moves through your large intestine too quickly, bile doesn’t have time to break down completely. The result is stool that retains some of that original green pigment. The faster the transit, the greener the stool. This is why diarrhea often has a greenish tint, regardless of what you ate.
Foods That Turn Stool Dark Green
The most common culprit is simply eating a lot of green vegetables. Kale, spinach, broccoli, and other leafy greens contain chlorophyll, the pigment that makes plants green. Eat enough of it, especially in concentrated forms like green smoothies or juices, and the pigment overwhelms the brown color bile normally produces. The darker and more concentrated the greens, the darker green your stool can become.
Green food coloring and dyes are another frequent cause. Flavored drink mixes, ice pops, frosted cupcakes, and candy can all produce surprisingly vivid green stool. Blue and purple dyes can have a similar effect, since blue mixed with the yellow-brown of bile creates green. If you recently ate something with artificial coloring, that’s likely your answer.
Iron Supplements and Medications
Iron supplements are well known for changing stool color, and dark green is one of the more common results. The iron itself isn’t fully absorbed, and the unabsorbed portion reacts with digestive enzymes to produce a deep green or even black-green shade. This is completely expected and not harmful. If you’ve recently started an iron supplement or a multivitamin with iron, that’s almost certainly the explanation.
Antibiotics can also cause green stool through a different mechanism. The bacteria in your gut that are responsible for converting bile pigments to brown can be killed off during a course of antibiotics. Without those bacteria doing their job, stool tends to come out green or yellowish until your gut flora recovers.
Infections and Rapid Transit
Bacterial infections from Salmonella or E. coli, viral infections like norovirus, and parasites like Giardia can all cause green diarrhea. These infections trigger a rapid “gush” through the intestines, so bile passes through unprocessed. The green color in these cases is less about the infection itself and more about how fast everything is moving.
The key distinction is what comes along with the color change. Infection-related green stool typically shows up alongside abdominal pain, fever, vomiting, or watery diarrhea. If you have green stool with no other symptoms, an infection is unlikely. Irritable bowel syndrome (IBS) can also speed up transit enough to produce green stool during flare-ups, particularly during episodes of diarrhea-predominant IBS.
Green Stool in Babies
Green poop in infants is common and has its own set of causes. Breastfed babies sometimes produce green stool when they don’t finish feeding entirely on one side, which means they get more of the thinner, lower-fat foremilk and less of the fattier hindmilk. This changes how the milk is digested and can give stool a greenish color.
Babies on protein hydrolysate formula, the type used for milk or soy allergies, frequently have green stool as a normal side effect. Newborns who are exclusively breastfed may also produce green stool simply because they haven’t yet developed the full range of intestinal bacteria needed to convert bile pigments to brown. Diarrhea in infants causes green stool for the same reason it does in adults: rapid transit.
When Green Stool Signals a Problem
A single episode of dark green stool, or even a few days of it, is almost never concerning if you feel fine otherwise. If you can trace it back to a meal, a supplement, or a bout of stomach upset, the color should return to brown within a day or two once the cause passes.
Pay closer attention if green stool persists for more than a few days without an obvious dietary explanation, or if it comes with fever, ongoing diarrhea, abdominal pain, weight loss, vomiting, or blood. These combinations can point to an infection, inflammatory condition, or malabsorption issue worth investigating. Stool that changes colors frequently without a clear pattern is also worth mentioning to a healthcare provider, since it can reflect ongoing digestive irregularities.