What could be causing my loose bowel movements that smell like acetone?

Loose Bowel Movements with Acetone Smell

Your loose bowel movements with an acetone smell strongly suggest ketosis or diabetic ketoacidosis (DKA), which requires immediate blood glucose and ketone testing to rule out a life-threatening metabolic emergency. 1, 2

Immediate Evaluation Required

Critical Tests to Obtain Now

• Blood glucose measurement - DKA is defined by glucose >250 mg/dL, and this is a medical emergency with 1-5% mortality 2
• Serum or urine ketone testing - elevated ketones (serum >0.5 mmol/L) combined with hyperglycemia confirms DKA 1
• Basic metabolic panel - check for anion gap metabolic acidosis (pH <7.3, bicarbonate <18 mEq/L) 2

Why Acetone Smell Matters

The acetone odor you're detecting is a hallmark sign of ketoacidosis - acetone is one of three ketone bodies produced when your body breaks down fat for energy instead of glucose, and it's volatile enough to be exhaled in breath and excreted in stool 1, 3, 4. This fruity/acetone smell is so characteristic that it can even trigger false-positive breathalyzer readings 4.

Most Likely Causes

Diabetic Ketoacidosis (Primary Concern)

• DKA occurs in both known diabetics and 33% of cases are in people without prior diabetes diagnosis 2
• Common precipitating factors include infection (most common), medication noncompliance, new-onset diabetes, or SGLT2 inhibitor use 1, 5
• Classic symptoms beyond diarrhea: polyuria (98%), polydipsia (98%), weight loss (81%), fatigue (62%), nausea/vomiting (46%), abdominal pain (32%) 2
• The loose stools occur because the metabolic derangement affects gut motility and the severe hyperglycemia causes osmotic diarrhea 2, 3

Ketogenic Diet or Fasting

• If you're following a very-low-carbohydrate ketogenic diet, nutritional ketosis can produce acetone smell without the dangerous acidosis of DKA 1
• However, this should be distinguished from pathologic ketoacidosis through blood testing 1

Alcoholic Ketoacidosis

• Can present similarly with ketone production and GI symptoms in the setting of alcohol use and poor nutritional intake 6

Red Flags Requiring Emergency Evaluation

Seek immediate medical attention if you have any of these alongside the acetone-smelling diarrhea:

• Kussmaul respirations (deep, rapid breathing) - this is your body trying to compensate for metabolic acidosis 3
• Altered mental status, lethargy, or confusion 2, 3
• Severe abdominal pain or persistent vomiting 2, 5
• Signs of dehydration/shock (hypotension, tachycardia, decreased urine output) 3
• Any known diabetes with recent illness or medication changes 1, 5

Diagnostic Algorithm

Step 1: Rule Out DKA (Urgent)

• Measure blood glucose immediately - if >250 mg/dL, proceed to emergency department 2
• Check urine ketones with reagent strips - highly sensitive for DKA with high negative predictive value 1
• If both elevated, obtain arterial blood gas, complete metabolic panel, and calculate anion gap 2

Step 2: If DKA Excluded, Evaluate Chronic Diarrhea Causes

Only proceed here if ketone testing and glucose are normal:

• Complete blood count and sedimentation rate (particularly important in younger patients for inflammatory conditions) 1, 7
• Celiac serology - crucial in younger patients as it's a common, treatable cause 7, 8
• Fecal calprotectin if under 45 years old to rule out inflammatory bowel disease 7
• Thyroid function tests - hyperthyroidism causes diarrhea and can alter metabolism 8
• Stool studies for ova and parasites based on exposure history 1, 7

Step 3: Consider Malabsorption if Stool Characteristics Suggest It

• If stools are bulky, pale, and malodorous (steatorrhea), evaluate for pancreatic insufficiency, bile acid malabsorption, or celiac disease 1, 8
• However, the acetone smell specifically points away from typical malabsorption and toward ketosis 1, 3

Critical Pitfall to Avoid

Do not dismiss the acetone smell as insignificant - this is a specific metabolic sign that warrants immediate glucose and ketone testing, even if you feel relatively well otherwise. DKA can progress rapidly over 24-48 hours and has significant mortality if untreated 2, 5. The presence of acetone in stool and breath indicates systemic ketone production that needs evaluation 3, 4.