A sweet or fruity scent in stool is an unusual phenomenon. While the typical odor of feces is unpleasant, a distinct change in aroma suggests an alteration in the chemical processes occurring within the body. This shift from a foul scent to a fruity one signals that digestion, metabolism, or the gut environment has changed significantly.
The Chemistry of Stool Odor
The characteristic strong odor of feces results from the breakdown of unabsorbed food matter by anaerobic bacteria in the large intestine. These gut microbes produce a mixture of volatile organic compounds (VOCs) during fermentation. Primary contributors are sulfur-containing compounds like hydrogen sulfide, which creates a rotten-egg smell, and methanethiol.
Nitrogen-containing molecules such as indole and skatole also contribute to the pungent smell. Skatole, also known as 3-methylindole, is a byproduct of the bacterial decomposition of the amino acid tryptophan. The combination of these sulfurous and nitrogenous compounds defines the noxious aroma of human waste.
Ketone Production and Diabetic Ketoacidosis
One concerning cause of a fruity or sweet odor relates to the body’s metabolic state, specifically the production of ketones. Ketosis occurs when the body, unable to use glucose for energy, begins to break down fat stores instead. This survival mechanism produces three types of ketone bodies: acetoacetate, beta-hydroxybutyrate, and acetone.
Acetone is a highly volatile compound that is chemically similar to nail polish remover and carries a noticeable sweet or fruity scent. While the body normally expels acetone primarily through the breath and urine, high concentrations can potentially lead to its presence in stool. An elevated level of ketones, combined with high blood sugar, can rapidly lead to a life-threatening condition called Diabetic Ketoacidosis (DKA).
DKA is most common in individuals with undiagnosed or poorly controlled Type 1 diabetes, where a severe lack of insulin prevents cells from utilizing glucose for fuel. The excessive production and accumulation of acidic ketones overwhelm the body, leading to metabolic acidosis.
Dietary and Digestive Factors
If the fruity smell is not related to a metabolic state like ketosis, it is often linked to the fermentation of unabsorbed simple sugars in the digestive tract. When the small intestine fails to properly break down or absorb certain carbohydrates, these molecules travel into the large intestine. There, the dense population of gut bacteria rapidly ferments the sugars, producing gases and short-chain fatty acids that can sometimes yield a sweet odor.
This effect can result from a sudden increase in artificial sweeteners, such as sorbitol or xylitol, or highly fermentable carbohydrates known as FODMAPs. Since these substances are poorly absorbed, they become readily available food sources for the gut flora. Malabsorption disorders, where the gut struggles to process nutrients like fructose or lactose, can also cause sugars to pass through undigested, resulting in a similar fermentation and scent profile.
Another digestive factor involves the disruption of the gut microbiome, which can be caused by recent antibiotic use. Antibiotics clear out both harmful and beneficial bacteria, allowing certain microbes to proliferate and change the chemical makeup of the stool. In rare cases, an infection with the bacterium Clostridioides difficile (C. diff) is known to produce an unusually sweet or sickly-sweet odor due to the compounds it releases.
Identifying Concerning Symptoms
While a change in diet or a course of antibiotics can often be the benign cause of a sweet-smelling stool, the possibility of a serious underlying condition means certain accompanying symptoms should not be ignored. The sudden onset of a fruity odor, especially alongside excessive thirst, frequent urination, or unexplained weight loss, requires urgent medical evaluation. These symptoms are closely associated with uncontrolled high blood sugar and the risk of DKA.
Other red flags that elevate concern include persistent diarrhea, severe abdominal pain, vomiting, or signs of confusion or fatigue. Any persistent change in stool odor that lasts longer than a few days, or is paired with any sign of systemic illness, warrants a consultation with a healthcare professional. A medical evaluation can determine if the scent is simply a dietary effect or a sign of a more significant metabolic or infectious process.