Urine that smells like butter or popcorn is usually a sign that your body is burning fat for fuel and releasing byproducts called ketones. This can happen from dietary changes, fasting, or unmanaged blood sugar levels. Less commonly, the smell comes from supplements, dehydration, or a bacterial infection. The odor itself is rarely dangerous, but it sometimes points to a condition worth checking on.
Ketones Are the Most Likely Cause
When your body doesn’t have enough carbohydrates for energy, it switches to burning stored fat instead. This process, called ketosis, produces three types of ketone bodies: acetoacetate, beta-hydroxybutyrate, and acetone. Your kidneys filter these compounds out through urine, and the mix can create a smell people describe as buttery, popcorn-like, or sweet. Acetone on its own tends to smell more like nail polish remover, but acetoacetate and its breakdown products contribute a richer, more butter-like note.
You don’t need to be on a strict ketogenic diet for this to happen. Skipping meals, fasting, intense exercise on an empty stomach, or simply eating fewer carbs than usual for a few days can push your metabolism into mild ketosis. The smell is typically strongest in the morning, when you’ve gone the longest without eating.
Unmanaged Diabetes Can Do the Same Thing
If you’re noticing a persistent buttery or sweet smell and you haven’t changed your diet, your blood sugar may be the issue. In diabetes, cells struggle to absorb glucose from the bloodstream. When they can’t get enough, the liver begins converting fat into ketones as an alternative fuel source. Those ketones spill into the urine in larger quantities than you’d see from simple dieting.
High blood sugar also causes the kidneys to dump excess glucose directly into urine, which can smell sweet, syrupy, or fruity on its own. The combination of sugar and ketones in urine often produces a distinctive sweet-buttery odor that people find hard to place. If you’re also experiencing unusual thirst, frequent urination, fatigue, or unexplained weight loss, those are signs that blood sugar levels need medical attention. A severe version of this, called diabetic ketoacidosis, can develop quickly and is a medical emergency.
B Vitamins and Supplements
B-complex vitamins are a well-known cause of unusual urine odor. Your body absorbs what it needs and excretes the rest, especially with water-soluble vitamins. The surplus can give urine a strong, unfamiliar smell that some people interpret as buttery or savory. You’ll often notice a bright yellow or neon color at the same time, which is a giveaway that supplements are the cause. Other water-soluble supplements can produce similar effects. If the smell appeared around the same time you started a new vitamin, multivitamin, or protein powder, that’s likely your answer.
Dehydration Concentrates the Smell
Sometimes the underlying cause of the odor is mild, but dehydration makes it noticeable. When you’re not drinking enough water, your urine becomes more concentrated. Compounds that would normally be diluted enough to be odorless become strong enough to detect. This is why buttery or unusual urine smells often seem worse first thing in the morning or after a workout. Drinking more water throughout the day and checking that your urine stays a pale straw color is a simple way to test whether dehydration is amplifying the smell.
Urinary Tract Infections
Bacterial infections in the urinary tract can produce foul or unusual-smelling urine. Certain bacteria, particularly types that break down urea (a normal waste product in urine), generate ammonia and other compounds that create strong, sometimes savory or rancid odors. The smell alone isn’t enough to diagnose an infection, but if it comes with burning during urination, cloudy or discolored urine, pelvic pressure, or a frequent urge to go, an infection is a strong possibility. A simple urine test can confirm or rule it out.
Protein Metabolism Disorders
Rarely, unusual urine odor comes from the body’s inability to break down certain compounds from food. Trimethylaminuria is one such condition, caused by a genetic variation that prevents an enzyme from processing a nitrogen-containing compound called trimethylamine. This typically produces a fishy odor rather than a buttery one, but the broader category of metabolic disorders can create a range of unexpected smells depending on which compounds accumulate. These conditions are uncommon and usually present from childhood, so they’re unlikely to explain a new smell in adulthood.
How to Narrow Down the Cause
Start with the simplest explanations. Think about what you’ve eaten in the last day or two. A low-carb meal pattern, a skipped lunch, or a heavy workout on light food intake can all trigger mild ketosis. Check whether you recently started any new supplements or vitamins.
Drink more water for a day or two and see if the smell fades. If it does, concentrated urine was likely making a minor odor more prominent. If the buttery smell persists for more than a few days despite normal eating, adequate hydration, and no new supplements, it’s worth getting a urine test. A basic urinalysis can detect ketones, glucose, and signs of infection, all of which point to the most common causes. The test is quick, inexpensive, and gives you a clear answer.