Dark green poop is usually harmless and caused by something you ate. Leafy greens, food dyes, iron supplements, and even blueberries can turn your stool noticeably green. In most cases, the color returns to brown within a day or two once the food or supplement passes through your system.
That said, dark green stool can sometimes signal that food is moving through your intestines faster than normal, or less commonly, a bacterial infection. Understanding the difference between a dietary quirk and something worth paying attention to comes down to context: what you’ve been eating, how long the color persists, and whether other symptoms show up alongside it.
Foods That Turn Stool Dark Green
The most common reason for green poop is simply eating green things. Spinach, kale, broccoli, avocados, herbs, and matcha all contain chlorophyll, the pigment that gives plants their color. Your body doesn’t fully break down chlorophyll during digestion, so eating a large salad or a green smoothie can produce stool that ranges from bright green to a deep, dark green.
Pistachios get their color from the same pigment and can have the same effect. Blueberries, despite being purple, can also produce green shades depending on how they interact with bile during digestion. Artificial food coloring is another frequent culprit. Brightly frosted cupcakes, candy, or drinks with synthetic dyes keep tinting whatever they touch as they move through your digestive tract. Even foods that aren’t green themselves can produce green stool if they contain blue or green dyes.
Iron Supplements and Medications
If you recently started taking iron supplements, dark green or even blackish-green stool is a predictable side effect. The iron itself changes color as it reacts with digestive enzymes, and the darker the green, the more iron your body is processing. This is not a sign that anything is wrong. Some antibiotics can also tint stool yellow or green by disrupting the normal balance of gut bacteria, which changes how bile is processed.
How Bile Affects Stool Color
Your liver produces bile, a bright green fluid that helps break down fats. As bile travels through your intestines, bacteria gradually change its color from green to yellow to brown. That final brown shade is what gives normal stool its color.
When food moves through your intestines faster than usual, bile doesn’t have enough time to complete that color shift. The result is green stool. This is why diarrhea often comes out green regardless of what you ate. Anything that speeds up transit time, whether it’s a stomach bug, stress, a high-fiber meal, or irritable bowel syndrome (IBS), can produce the same effect. The green color in these cases reflects incomplete bile processing, not the presence of something dangerous.
Medical Causes Worth Knowing
While diet and transit time explain the vast majority of dark green stool, a few medical conditions can also be responsible. Bacterial infections in the gut, such as Salmonella, can cause persistent green diarrhea along with cramping, fever, and nausea. IBS can produce green stool during flare-ups, particularly when diarrhea is the dominant symptom.
The color itself is rarely the concerning part. What matters more is the full picture. Green stool that shows up once after a big plate of spinach is completely different from green diarrhea that lasts several days with a fever. If your stool doesn’t return to brown within a few days, or if you’re also dealing with pain, dehydration, or fever, that combination is worth getting checked out. Drink plenty of fluids if diarrhea is involved, since dehydration is the more immediate risk in those situations.
For reference, the stool colors that raise more serious concern are red and black, which can indicate bleeding somewhere in the digestive tract. Dark green on its own, without blood or tarry black streaks, is far less likely to point to something urgent.
Green Stool in Babies
Green poop in infants is extremely common and almost always normal. In the first few days of life, newborns pass meconium, a dark greenish-black stool that clears out material accumulated before birth. After that, breastfed babies can produce green stool for several reasons: not finishing a full feeding on one side (which means they get more of the thinner, lower-fat milk), a still-developing population of gut bacteria, or simply having a bout of diarrhea.
Babies on protein hydrolysate formula, the type used for milk or soy allergies, also tend to produce greener stool. As long as the baby is gaining weight, feeding well, and doesn’t have a fever, green poop in an infant is rarely a problem. Persistent green diarrhea in a baby, however, warrants a call to the pediatrician because infants dehydrate much faster than adults.
How Long Green Stool Typically Lasts
If the cause is dietary, your stool should return to its normal brown color within one to three bowel movements, depending on how quickly food moves through your system. If you stop eating the food in question and the green persists for more than a few days, that’s a sign something else may be going on, whether it’s a medication effect, an ongoing infection, or a digestive issue affecting how quickly food passes through your gut.