Tomatoes can harmlessly turn your stool red, a common observation that often causes alarm. This predictable result occurs because certain food components pass through the digestive tract largely intact. Recognizing this natural process helps demystify the startling change in appearance.
Why Tomatoes Can Survive Digestion
The vibrant red color of a tomato comes from lycopene, a carotenoid pigment embedded within the plant’s cell walls. The human digestive system lacks the specific enzymes needed to completely break down the tough, outer layers of plant material, especially the tomato skin. This outer layer is primarily cellulose, an insoluble dietary fiber that resists digestion and adds bulk to the stool.
Lycopene is a fat-soluble compound that must be released from the cellular matrix before it can be absorbed. While cooking tomatoes helps disrupt these cell walls and increases the pigment’s bioavailability, consuming raw or lightly processed products allows a significant amount of the pigment to remain unreleased. This undigested lycopene remains protected by the cellulose and passes through the gastrointestinal tract, resulting in a noticeable red hue.
Identifying the Source of Red Stool
The appearance of red stool raises concerns about internal bleeding, but the cause is dietary in most cases. Distinguishing harmless food pigment from blood involves examining the physical characteristics of the color. Redness caused by tomatoes often appears patchy, streaky, or as recognizable particles of skin or seeds scattered within the stool. These undigested remnants typically do not dissolve in the toilet water and will not leave a uniform red stain on the toilet paper.
Blood presents differently depending on where the bleeding originates in the gastrointestinal tract. Bright red blood (hematochezia) suggests bleeding lower down, such as from hemorrhoids or a fissure. It often appears as streaks on the outside of the stool or stains the water uniformly red. Darker, maroon, or black, tarry stools (melena) indicate bleeding higher up in the stomach or upper small intestine, where stomach acid has altered the blood. The absence of other physical symptoms, such as fever, abdominal pain, dizziness, or vomiting, strongly indicates a dietary source. If the redness persists after stopping red foods, or if it is accompanied by concerning symptoms, medical evaluation is warranted.
Other Foods That Change Stool Color
Tomatoes are not the only food capable of altering waste color, as many deeply pigmented foods survive the digestive process.
Common Dietary and Medicinal Causes
- Beets contain the reddish-purple pigment betanin, which can turn stool pink or deep red.
- Products with high concentrations of artificial food coloring, such as red gelatin, soft drinks, or brightly colored frostings, can tint the stool.
- Dark blue or purple foods, like blueberries or black licorice, may result in a stool color that appears dark green or black due to concentrated natural pigments.
- Excessive consumption of dark leafy greens, such as spinach, can lead to a green-tinged stool because of the high chlorophyll content.
- Certain medications and supplements, including iron supplements or bismuth subsalicylate, can also cause the stool to become dark or black.