Most Likely Causes (Ranked)
When you're dehydrated, urine becomes more concentrated. Normal metabolic byproducts — including trace ketones and diacetyl — that are usually diluted enough to be odorless become concentrated enough to detect. This is the simplest and most common cause.
Low-carb and keto diets force the body to burn fat for energy, producing ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone). These ketones are excreted in urine and produce a sweet, buttery, or popcorn-like smell. High protein intake also increases urea and branched-chain amino acid metabolites.
Pregnancy hormones (particularly hCG) change metabolism, and many pregnant women experience ketosis, especially in the first trimester due to morning sickness and reduced carb intake. Gestational diabetes in the second/third trimester also causes ketone buildup.
In Type 1 or Type 2 diabetes, the body can't properly use glucose. It burns fat instead, producing high levels of ketones. When ketones build up excessively, they spill into the urine, creating a sweet or popcorn-like smell. This can be an early warning sign of diabetes.
Fenugreek (produces sotolon — maple syrup/butterscotch smell), asparagus, coffee, garlic, and some B vitamins can change urine odor. Meal replacement shakes (like Huel) with certain artificial flavors can produce a popcorn-like urine smell.
How to Fix It
Increase Water Intake
$0First step — works for the most common cause.
- 1Drink at least 64-80 oz of water daily. On keto, aim for 100+ oz.
- 2If urine is dark yellow, you need more water. Aim for pale straw-colored urine.
- 3Drink a large glass of water first thing in the morning to address overnight dehydration.
- 4If the smell resolves with hydration, dehydration was the cause.
Adjust Diet if Needed
$0If dietary ketosis is producing the smell.
- 1On keto: the smell is expected and harmless. It often diminishes after 2-4 weeks of adaptation.
- 2If the smell bothers you, adding 20-50g more carbs per day can reduce ketone production while keeping you in mild ketosis.
- 3Reduce BCAA supplements if you're taking them — these contribute to the buttery smell.
- 4Track the smell against your protein intake to identify your personal threshold.
Check Blood Sugar
$15-100If no dietary explanation exists.
- 1Buy an at-home glucose meter ($15-30 at any pharmacy) and test fasting blood sugar.
- 2Normal fasting glucose: 70-99 mg/dL. Prediabetic: 100-125. Diabetic: 126+.
- 3If elevated, see your doctor for an A1C test, which shows your average blood sugar over 3 months.
- 4Urine ketone test strips ($8-15) can confirm whether ketones are present.
When to Call a Professional
Popcorn urine + extreme thirst + frequent urination + weight loss — get tested for diabetes immediately.
Popcorn urine + nausea/vomiting + confusion (especially in a diabetic) — possible DKA. Seek emergency care.
Popcorn urine during pregnancy — mention it to your OB/GYN as it may indicate gestational diabetes.
Persistent unusual urine odor for more than a week with no dietary explanation — warrants medical evaluation.
How to Prevent It
Stay well-hydrated — dilute urine means dilute (undetectable) odor.
Monitor blood sugar if you have diabetes risk factors.
Track dietary changes vs. urine changes to identify triggers.
Regular annual blood work catches prediabetes before it progresses.
The Ketone Connection
The 'popcorn' smell specifically comes from diacetyl (2,3-butanedione), the same compound that gives movie theater popcorn its buttery aroma. Diacetyl is a metabolic byproduct that appears in small quantities during normal metabolism but increases significantly during ketosis. It's produced alongside the three main ketone bodies: acetoacetate, beta-hydroxybutyrate, and acetone.
In urine, these compounds are usually present at levels below the detection threshold (you can't smell them). But when concentrated by dehydration, or when ketone production is elevated from diet or diabetes, concentrations rise above the ~0.1 ppm detection threshold for diacetyl. Fun fact: the same compound is used as an artificial butter flavoring in microwave popcorn, which is why the association is so specific.
Frequently Asked Questions
No — the most common causes are dehydration and dietary ketosis. Diabetes is a possibility only if the smell persists without a dietary explanation and is accompanied by other symptoms.
It typically appears in the first 1-3 weeks and diminishes as your body becomes more efficient at using ketones. Staying very hydrated helps reduce the concentration.
Yes — dehydration concentrates all urinary metabolites, including diacetyl and other ketone-related compounds that produce the buttery popcorn smell.
If it resolves with hydration or has a clear dietary cause, no. If it persists for more than a week without explanation, or you have symptoms of diabetes, see a doctor.
Related but different. Sweet/fruity urine is more associated with high ketone or sugar levels (diabetes). Popcorn/buttery is specifically associated with diacetyl from mild ketosis or dehydration.