Why Does My Poop Smell Like Cabbage?

Cabbage and stool share a surprisingly overlapping set of sulfur-containing chemicals, so when your poop smells like cabbage, it usually means your gut bacteria have been busy breaking down sulfur-rich foods or amino acids into the same volatile compounds that give cruciferous vegetables their distinctive funk. The overlap is not a coincidence: the methyl sulfides responsible for most of what we recognize as “fecal odor” belong to the same chemical family as the compounds that give cabbage, broccoli, and Brussels sprouts their smell. Whether the trigger is last night’s coleslaw or something happening deeper in your digestive system, the explanation starts with sulfur.

Why Cabbage and Stool Smell Alike

For decades, textbooks blamed two compounds called skatole and indole for the smell of stool. Research using gas chromatography and mass spectrometry overturned that assumption, finding that the dominant odor-producing chemicals in feces are actually methyl sulfides: methanethiol, dimethyl disulfide, and dimethyl trisulfide.¹ These sulfur-based molecules are pungent at extremely low concentrations, which is why even a small shift in their production can make a big difference to your nose.

Cabbage and its relatives in the Brassica family are loaded with their own sulfur compounds. When you chop, cook, or chew them, they release sulfides, polysulfides, isothiocyanates, and thiols, all of which contribute to that sharp, slightly rotten-egg aroma.² Once these compounds reach your large intestine, gut bacteria further metabolize them into the same methyl sulfides that define fecal odor. So if you eat cabbage, you are literally feeding your colon the raw ingredients for a more cabbage-scented output.

What Your Gut Bacteria Do With Sulfur

Your colon is home to trillions of microorganisms, and several groups specialize in processing sulfur. Sulfate-reducing bacteria are the main producers of hydrogen sulfide in the gut, using sulfate as a fuel source. But they are not the only contributors. Other bacteria break down the sulfur-containing amino acid cysteine through a process that also releases hydrogen sulfide.³ Hydrogen sulfide itself has that classic rotten-egg smell, and it serves as a precursor to the methyl sulfides that dominate stool odor.

The composition of your personal microbiome matters here. Two people eating the same cabbage-heavy meal can produce very different odors because one person’s gut may harbor more sulfate-reducing bacteria than the other’s. The microbiome also shifts in response to habitual diet. If you regularly eat high-sulfur foods, the bacterial populations that thrive on sulfur tend to grow, which can amplify the effect over time. Conversely, someone who rarely eats cruciferous vegetables and then has a big serving may notice a particularly dramatic change because their gut flora suddenly gets a sulfur windfall it is not accustomed to handling smoothly.

Foods Beyond Cabbage That Trigger the Same Smell

Cabbage gets the blame because it is one of the most sulfur-rich everyday foods, but the entire Brassica family shares this trait. Broccoli, Brussels sprouts, cauliflower, kale, and bok choy all contain high levels of the same sulfur-based flavor compounds.² Garlic and onions belong to the Allium family and deliver a different mix of sulfur compounds, but the endpoint in the colon is similar: more raw material for bacteria to convert into smelly sulfides.

Protein-rich foods also contribute, because the amino acids methionine and cysteine are both sulfur-containing. Research on how dietary methionine influences excreta odor found that higher methionine intake produced significantly higher concentrations of methanethiol, dimethyl disulfide, and dimethyl trisulfide.⁴ In plain terms, a high-protein meal heavy in eggs, red meat, or dairy gives your gut bacteria more sulfur amino acids to work with, which can push stool odor in that cabbage-like direction even if you have not touched a vegetable.

Beer and wine deserve a mention too. Both contain sulfites and sulfur compounds from fermentation, and beer especially can deliver meaningful amounts of sulfate to the colon. A night of heavy drinking can shift colonic chemistry toward more hydrogen sulfide production, which might explain why the morning after smells particularly rough.

How Transit Time Affects Odor

The speed at which food moves through your digestive tract plays a surprisingly large role in what your stool smells like. A study of healthy volunteers found that shorter transit times were associated with higher counts of sulfate-reducing bacteria and higher concentrations of fermentation byproducts, including short-chain fatty acids.⁵ When food moves quickly through the colon, the environment tends to favor bacteria that produce hydrogen sulfide rather than bacteria that consume it (such as methane-producing organisms, which were less abundant in faster-transit individuals).

This has a practical implication: anything that speeds up your digestion can change stool odor. A high-fiber meal, a strong cup of coffee, a stomach bug, stress, or even certain medications that increase gut motility can all accelerate transit and shift the balance toward more sulfur-producing bacteria. If you notice the cabbage smell on days when your bowel movements are looser or more frequent than usual, faster transit is a likely factor, even if your diet has not changed.

Slower transit, on the other hand, gives methane-producing microorganisms more time to consume hydrogen in the colon, which can actually reduce sulfide production. People who tend toward constipation may notice a different odor profile than people who tend toward faster bowel habits, and neither pattern is inherently a problem as long as it is consistent for you.

When to Consider a Medical Cause

Most of the time, cabbage-scented stool is a dietary issue and nothing more. But a persistent change in stool odor, especially one that does not track with what you have been eating, can occasionally signal something that deserves attention.

Inflammatory bowel disease is one condition where clinicians and patients both report noticeable changes in fecal odor during flare-ups. The volatile organic compound profile of stool shifts during active inflammation, and researchers have explored whether these odor changes could even serve as a diagnostic marker.⁶ If you are having persistent changes in stool odor alongside symptoms like cramping, blood in the stool, or unintentional weight loss, it is worth bringing up with a doctor.

Bile acid diarrhea is another condition that changes stool character. People with this condition have accelerated colonic transit and an altered stool microbiome, with reduced conversion of primary bile acids to secondary bile acids.⁷ The altered bacterial activity and faster transit can both shift the odor profile. Bile acid diarrhea is underdiagnosed and often mistaken for irritable bowel syndrome, so if you have chronic watery diarrhea with unusually pungent stool, it may be worth asking about specifically.

Malabsorption of any kind can worsen stool odor because undigested nutrients reaching the colon become extra fuel for bacterial fermentation. Conditions affecting the pancreas, celiac disease, and lactose intolerance can all increase the load of unabsorbed material that bacteria ferment, potentially amplifying sulfur compound production. The accumulation of odorous compounds can also result from compromised function of the liver or kidneys, not just the gut itself.⁸

Sugar Alcohols and Artificial Sweeteners

If you have not changed your vegetable or protein intake but have recently started consuming more sugar-free products, the culprit might be sugar alcohols. Sweeteners like xylitol, sorbitol, and maltitol are poorly absorbed in the small intestine, so a large fraction of what you consume reaches the colon intact. There, bacteria ferment it, producing gas and sometimes shifting the odor of stool. At higher doses, sugar alcohols can cause osmotic diarrhea, which speeds transit and can further change the smell.⁹ The good news is that many people adapt over days to weeks as their gut bacteria adjust to the new substrate, so the smell may ease if your intake stays consistent.

Trimethylaminuria and Systemic Odor Conditions

Rarely, an unusual body or stool odor has a genetic basis. Trimethylaminuria, sometimes called fish malodor syndrome, is a condition in which the body cannot fully break down trimethylamine, a compound produced during digestion of certain foods. In healthy people, more than 90% of trimethylamine is converted to an odorless form before being excreted.¹⁰ People with trimethylaminuria excrete excess free trimethylamine, which has a strong fishy or sulfurous smell that can show up in urine, sweat, breath, and stool. The smell is usually described as more fishy than cabbage-like, but some people perceive it differently, and the overlap in sulfur chemistry means the distinction is not always clean.

Trimethylaminuria is quite rare, so it is not a likely explanation for most people reading this article. However, if you have a persistent body odor or stool odor that does not respond to dietary changes and has been present since childhood or adolescence, it may be worth discussing with a doctor who can order a urine test for trimethylamine levels.

Why You Can Smell It So Easily

Part of the reason this kind of stool odor catches your attention is that human noses are extraordinarily sensitive to sulfur compounds. This is not a fluke. Research on olfactory receptors shows that at least one human receptor for thiols (low-molecular-weight sulfur compounds) requires copper ions to function, and this receptor responds to sulfur-containing gases at remarkably low concentrations.¹¹ From an evolutionary standpoint, being able to detect even trace amounts of sulfur gas was useful for avoiding spoiled food, low-oxygen environments, and predators. The downside of this finely tuned alarm system is that a modest uptick in sulfide production in your colon registers as a dramatic change in smell, even if nothing is medically wrong.

This also explains why you might notice a cabbage-like stool odor that your partner or housemate claims they cannot detect. Individual variation in olfactory receptor genes means some people are much more sensitive to specific sulfur compounds than others. You may be picking up on a change that is real but objectively quite small in chemical terms.

Practical Ways to Reduce the Smell

No universal treatment exists for unusually smelly stool, and evidence-based guidelines for managing fecal odor are limited.⁸ That said, a few strategies are worth trying if the smell bothers you:

• Track your diet: Keep a simple food diary for a week or two and note what you ate the day before any particularly pungent bowel movements. If cruciferous vegetables, garlic, onions, eggs, or high-protein meals reliably precede the smell, you have your answer. You do not necessarily need to eliminate these foods entirely; reducing serving sizes or spreading them across multiple meals can lower the sulfur load your colon receives at once.
• Stay hydrated: Adequate water intake supports normal transit time and dilutes the concentration of fermentation products in the colon. Dehydration slows things down, but it can also concentrate odorants in a smaller stool volume.
• Moderate alcohol intake: Cutting back on beer and wine reduces the sulfate and sulfite load reaching the colon, which in turn reduces hydrogen sulfide production.
• Gradually introduce high-fiber foods: Sudden large increases in fiber, especially from cruciferous vegetables, overwhelm the gut’s ability to process them smoothly. Increasing fiber intake slowly over a couple of weeks gives your microbiome time to adapt.
• Check your supplements: Some protein supplements, particularly those high in methionine or cysteine (common in whey protein concentrates), can increase sulfur compound production. If you started a new supplement around the time the smell changed, that is a reasonable suspect.

Electronic Noses and the Future of Stool Diagnostics

The volatile organic compounds in stool are not just a nuisance; researchers are actively developing technology to use them for medical diagnosis. Electronic nose devices use sensors paired with pattern-recognition algorithms to detect specific combinations of gases in stool samples, and early work suggests these patterns can distinguish between healthy individuals and those with gastrointestinal diseases.¹² The idea is that different diseases produce different “smell fingerprints” because they alter the microbiome and its metabolic output in characteristic ways.

This technology is still largely experimental, but it is a genuinely interesting frontier. Current diagnostic methods for many gut conditions involve invasive procedures like colonoscopy or time-consuming stool cultures. If a device could reliably screen for conditions like inflammatory bowel disease or certain infections just by analyzing the gases above a stool sample, it would make early diagnosis faster, cheaper, and far more pleasant for patients. For now, though, the best diagnostic tool for occasional cabbage-smelling stool remains a food diary and a bit of patience.