Green poop is almost always harmless. It usually means you ate something rich in green pigment, or food moved through your intestines faster than usual. In both cases, the color comes down to one thing: how your body processes bile, the yellow-green digestive fluid your liver produces to break down fat.
Bile starts out green. As it travels through your intestines, bacteria break it down and it gradually shifts from green to yellow to brown. Anything that shortens that journey or adds extra green pigment to the mix can leave you with a surprisingly green result in the toilet.
Green Foods Are the Most Common Cause
If you’ve been eating a lot of leafy greens, that’s your answer. Spinach, kale, broccoli, and other dark green vegetables are packed with chlorophyll, the pigment that makes plants green. Your body doesn’t fully break chlorophyll down, so it passes through and tints your stool. The more you eat, the more vivid the color.
Leafy greens aren’t the only culprits. Pistachios get their green color from chlorophyll and other plant pigments. Avocados, fresh herbs, and matcha (powdered green tea) can all do the same thing. Even bright-colored frosting, candy, or drinks with artificial food dyes can turn your stool unusual shades, green included. The dye keeps tinting whatever it touches as it moves through your digestive tract.
Fast Digestion and Diarrhea
When food moves through your intestines quickly, bile doesn’t have enough time to complete its color change from green to brown. The result is stool that looks green, sometimes bright green. This is especially common during a bout of diarrhea, a stomach virus, or food poisoning, where everything is being pushed through at high speed.
You might also notice green stool after eating something that didn’t agree with you, during a stressful period, or any time your gut is more active than usual. Once your digestion returns to its normal pace, the color will follow.
Iron Supplements and Medications
Iron supplements are a well-known cause of dark green stool, sometimes so dark it looks almost black. This is a normal side effect, and some physicians actually consider it a sign that the iron is being absorbed properly. If the color bothers you, a lower dose may help, but it’s worth checking with whoever prescribed the supplement before adjusting.
Certain antibiotics can also cause green stool by disrupting the balance of gut bacteria. Since those bacteria are responsible for breaking bile down into its final brown color, killing some of them off temporarily changes the equation. The color typically returns to normal once you finish the course of medication and your gut bacteria recover.
Green Stool in Babies
Green poop in infants is common and rarely a concern, but the causes differ from adults. A newborn’s very first bowel movements (meconium) are dark green to black, which is completely normal. In the days and weeks that follow, stool color can range widely.
Breastfed babies sometimes produce green stool if they aren’t finishing a full feeding on one side before switching. The earlier portion of breast milk is lower in fat, and missing the higher-fat milk that comes later can affect how the baby digests it. Babies on protein hydrolysate formula, the type used for milk or soy allergies, also tend to have green stool. Breastfed infants who haven’t yet developed a full community of intestinal bacteria may see green stool as well. In all of these cases, the baby is typically healthy.
Diarrhea in infants can also cause green stool for the same reason it does in adults: bile moves through too quickly to change color. If your baby has diarrhea along with green stool, staying on top of hydration is the priority.
When Green Stool Signals Something More
A day or two of green stool after a big salad or a stomach bug is nothing to worry about. But green stool that persists for more than a few days without an obvious dietary explanation is worth bringing up with a doctor.
Pay closer attention if the green stool comes with diarrhea that won’t quit, fever, stomach cramps, or signs of dehydration like dizziness, dry mouth, or dark urine. These symptoms together can point to an infection or inflammation that needs treatment. In young children and infants, dehydration develops faster, so persistent diarrhea with green stool warrants quicker attention.
On its own, green poop is one of the least worrying color changes your stool can make. Red or black stool (when you haven’t eaten beets or taken iron) is far more clinically significant, since those colors can indicate bleeding in the digestive tract. Green, by comparison, is usually just your dinner making its presence known.