Urine that smells like butter is usually caused by specific chemical compounds your body produces during normal metabolism or in response to certain health conditions. The buttery smell most often traces back to a compound called diacetyl (or its close relative acetoin), the same molecule that gives movie-theater popcorn and actual butter their characteristic aroma. Several situations can cause these or similar compounds to show up in your urine.
Ketones and a High-Fat Diet
When your body burns fat for fuel instead of carbohydrates, it produces ketone bodies as a byproduct. This happens during low-carb or ketogenic diets, fasting, or when you skip meals for an extended period. Ketones are excreted through both your breath and your urine, and they can create a range of unusual smells, from fruity and sweet to something closer to buttery or oily.
If you’ve recently changed your diet to include more fat and fewer carbs, this is one of the most common explanations. The smell typically becomes noticeable within a few days of entering ketosis and often fades as your body adapts to burning fat more efficiently. Staying well-hydrated helps dilute the concentration of ketones in your urine and reduces the intensity of the odor.
For people with diabetes, a strong, unusual urine smell can signal diabetic ketoacidosis, a serious condition where ketone levels climb dangerously high. This is more likely if the smell is accompanied by excessive thirst, frequent urination, nausea, or confusion. In that case, it’s a medical emergency rather than a dietary quirk.
Bacterial Infections That Produce Buttery Compounds
Certain bacteria that cause urinary tract infections literally manufacture the compound responsible for a butter-like smell. Species in the Klebsiella, Enterobacter, and Serratia families use a metabolic pathway called 2,3-butanediol fermentation, which produces acetoin and 2,3-butanediol as byproducts. Acetoin is a direct precursor to diacetyl, the molecule most closely associated with a buttery aroma.
Unlike a typical E. coli UTI, which tends to produce a more ammonia-heavy or generally foul odor, infections involving these acetoin-producing bacteria can give urine a distinctly buttery or popcorn-like quality. You might also notice cloudiness, a burning sensation when urinating, increased urgency, or pelvic discomfort. If the buttery smell persists for more than a day or two and is paired with any of these symptoms, a urine culture can identify the specific bacteria involved so it can be treated appropriately.
B Vitamins and Supplements
B-complex vitamins are one of the most common supplement-related causes of changes in urine smell. They’re water-soluble, so your kidneys flush out whatever your body doesn’t absorb, often turning your urine bright yellow in the process. The excess compounds and fillers in the supplement can also alter the scent in ways people describe as fatty, yeasty, or buttery.
If you recently started a new multivitamin or B-complex supplement and noticed the change, that’s likely the explanation. The smell should be consistent with when you take the supplement and will disappear if you stop taking it for a few days. Other water-soluble supplements can have similar effects.
Dehydration Concentrates the Smell
Sometimes the buttery compounds were always there in trace amounts, but dehydration made them noticeable. When you don’t drink enough water, your urine becomes more concentrated, and every dissolved compound, including the ones that create odor, is present in a higher ratio. What might be an undetectable hint of butteriness in diluted urine becomes obvious when the urine is dark yellow or amber.
Drinking enough fluid to keep your urine a pale straw color is the simplest way to test whether dehydration is amplifying an otherwise harmless smell.
Rare Metabolic Conditions
A few inherited metabolic disorders can cause unusual urine odors, though these are uncommon and almost always diagnosed in infancy. The most well-known is maple syrup urine disease (MSUD), where the body can’t properly break down certain amino acids found in protein. The buildup produces a compound called sotolone, the same molecule found in actual maple syrup and fenugreek. Sotolone’s aroma sits somewhere between caramel, maple, and butter, which is why some people describe it as buttery rather than sweet.
MSUD affects roughly 1 in 185,000 newborns and is caught through routine newborn screening in most countries. Adults who notice a new buttery urine smell are extremely unlikely to have an undiagnosed case. However, milder “intermediate” forms of the condition do exist and can become noticeable during periods of illness or high protein intake.
Foods That Change Urine Odor
Your kidneys filter out the breakdown products of everything you eat, and some foods produce metabolites with a buttery or rich scent. Fenugreek is a notable example: it contains sotolone, and people who consume fenugreek supplements or dishes heavy in fenugreek spice often report a maple or butter-like smell in their urine and sweat within hours. Asparagus is famous for producing a sulfurous odor, but less commonly discussed foods like certain cheeses, butter-heavy dishes, and foods cooked with diacetyl-containing flavorings can also shift urine toward a buttery scent as their components are metabolized and excreted.
If you can link the smell to a specific meal or ingredient, it will typically resolve within 24 to 48 hours as your body finishes processing those compounds.