Intestinal Candidiasis

Candidiasis is a fungal infection caused by Candida, a genus of yeast that lives on the skin and inside of the mouth, throat, vagina, and GI tract. Intestinal candidiasis refers specifically to an abnormally high level of Candida detected in samples from feces, rectal swabs, or (rarely) the intestinal mucosa (the lining of the stomach or intestinal tract).

IC does not appear to have perceptible symptoms.^[1]

Controversial publications from the 1970s and ’80s claimed that intestinal Candida overgrowth lead to a long list of ailments, including fatigue, GI discomfort, recurring yeast infections, arthritis, acne, migraine headache, and heart issues, although most of these claims have been debunked.^[1]

IC may lead to diarrhea associated with antibiotics and irritable bowel syndrome with diarrhea (IBS-D), but more research is needed.

Intestinal yeast colonization is estimated from rectal swabs, fecal samples, mucosal samples, or duodenal samples (from the area connecting the stomach and small intestine). Clinical scoring systems, such as the Candida score and Candida index, estimate the risk of developing systemic fungal infections in critically ill patients, and include the extent of Candida colonization at multiple body sites in conjunction with other factors (e.g., length of hospital stay, prior use of antibiotics, prior surgery, and illness severity).

An average fecal sample is expected to contain less than 10^4 colony-forming units (CFU) per milliliter (mL), but there is no consensus on the correct threshold for IC diagnosis.^[1][2] Studies generally classify a concentration of 10^3 to 10^5 CFU/mL as IC.

IC doesn’t require treatment in otherwise healthy people. In premature babies and critically ill patients, reducing or limiting intestinal Candida colonization lowers the risk of developing a systemic fungal infection. This is commonly done with antifungal drugs.

Although probiotics aren’t likely to prevent invasive fungal infections, it appears that they can reduce the risk of Candida colonization in premature babies and critically ill children.^[3][4]

Vitamin D supplementation may be effective for reducing the prevalence of Candida colonization as well as systemic Candida infection (as measured by blood and urine levels of Candida).

Some studies have also investigated medium-chain triglycerides (MCT) with and without vitamin D. These results are promising, but preliminary.^[5][6]

Certain compounds extracted from oregano, pine, cinnamon, and coffee suppress Candida growth in cell culture models and denture stomatitis (mild oral inflammation due to thrush), but these haven't been studied in the human GI tract.^[7][8]

Contrary to popular belief, refined carbohydrate intake doesn’t increase the risk of developing IC, and most yeast found in stool is likely derived from food and saliva.^[9][10]

Unlike the microbiome, the mycobiome (i.e., the fungal microbiome, which includes Candida) is more closely associated with recent dietary patterns than with long-term habits. Although high-carb diets may produce short-term increases in Candida, they don’t seem to increase risk of IC, and low-carb diets (as well as low-yeast diets) don’t meaningfully affect the risk or severity of IC, either.^[9][11][12]

There is little-to-no research on other treatments for IC.

Most cases of IC (and subsequent invasive infection) are seen in preterm infants and critically ill or immunocompromised individuals. Additionally, certain medications, such as antibiotics and steroids, permeable intestines, invasive surgical procedures, hospitalization, and the use of broad-spectrum antibiotics make premature infants more prone to IC and invasive infections.^[3]

People with diabetes may also be more prone to IC, but these findings are complicated by this population’s comparatively high use of antifungals, antibiotics, and steroids (to control inflammation). Intestinal Candida counts can also be elevated as a result of swallowing oral Candida, and oral candidiasis (overgrowth of yeast in the mouth and throat) can occur in people who wear dentures or take the aforementioned medications.^[12][13][14]