SIFO: Symptoms, Causes, and What the Research Says About Treatment

Something feels off in your gut — recurring bloating, gas, belching, or nausea you just can't explain. One reason doctors increasingly investigate: small intestinal fungal overgrowth (SIFO), a condition where too much fungus takes hold in the small intestine. Two clinical studies involving 244 participants with unexplained gastrointestinal symptoms found that roughly 1 in 4 had SIFO — 26% in one study (24 of 94 patients) and 25.3% in the other (38 of 150).

What Is SIFO?

Small intestinal fungal overgrowth is exactly what the name describes: an excessive number of fungal organisms in the small intestine, associated with gastrointestinal symptoms. It is not the same as SIBO (small intestinal bacterial overgrowth), though both share overlapping symptoms and can occur together.

Condition	Overgrowth type	Primary symptoms
SIFO	Fungal (most often Candida)	Bloating, gas, belching, nausea, diarrhea, indigestion
SIBO	Bacterial	Bloating, gas, diarrhea, abdominal pain

Candida — a yeast that normally lives in the gut, mouth, and elsewhere — is by far the most common fungal organism associated with SIFO. In healthy amounts Candida causes no problems; it only becomes an issue when the conditions in the small intestine allow it to multiply unchecked.

Candida is also linked to a wider range of gastrointestinal conditions, including IBS, Crohn's disease, and ulcerative colitis. If you want to know what Candida levels look like in your own gut, a whole-gut microbiome test can show you.

Symptoms of SIFO

The symptoms of SIFO closely overlap with other gut conditions — which is exactly why testing matters rather than guessing. Common signs include:

• Bloating
• Gas
• Belching
• Abdominal pain or discomfort
• Nausea
• Diarrhea
• Indigestion

What Causes SIFO?

Several factors can tip the small intestine's balance toward fungal overgrowth:

• Proton pump inhibitors (long-term use) — PPIs reduce stomach acid, which is one of your body's defenses against fungi and bacteria entering the small intestine. Low stomach acid raises the risk of GI overgrowth.
• Intestinal dysmotility — When the muscles of the small intestine move food through too slowly (a condition called dysmotility), it creates conditions where fungi can establish themselves. Dysmotility can be driven by conditions like diabetes, lupus, and Ehlers-Danlos syndrome.
• Frequent antibiotic use — Antibiotics can't distinguish between harmful and helpful gut microbes. As they clear problematic bacteria, they also remove the protective bacteria that keep fungi in check.
• Immunosuppressive medications — Drugs that dampen immune function reduce the body's ability to control fungal growth.
• Colectomy — A 2018 study (Rao et al., Clinical and Translational Gastroenterology) found that patients with colectomy had a significantly higher prevalence of combined SIBO/SIFO (24% vs 8% in controls, p = 0.017), and SIFO alone trended higher. The authors concluded that colectomy is a risk factor for intestinal overgrowth.

How Is SIFO Diagnosed?

The world of gut health tests continues to expand, but for SIFO specifically, the reference standard is a small bowel aspirate. During an upper endoscopy, a gastroenterologist passes a scope into the small intestine, collects a fluid sample from the duodenum, and sends it to a lab to look for elevated fungal counts.

At-home stool microbiome tests like Flore's can detect Candida and other fungi as part of the broader gut community — useful context for you and your clinician — but they test the colon contents, not the small intestine directly. SIFO diagnosis requires the aspirate.

How Doctors Approach SIFO

1. Antifungal medication

Once SIFO is confirmed by aspiration, the standard first step is a course of antifungal medication (typically fluconazole or nystatin) prescribed by your doctor. The 2015 Erdogan and Rao review noted that a 2–3 week antifungal course may improve symptoms, though evidence for complete eradication remains limited.

2. Probiotics as gut support

Probiotics come up often in SIFO conversations. A 2006 study found that Lactobacillus acidophilus therapy shortened the duration of fungal colonization of GI mucosa in experimental models. However, no clinical trials have shown probiotics alone clear SIFO. Think of them as a way to support the healthy microbial community alongside — not instead of — your doctor's plan.

3. Dietary changes

Some clinicians suggest a lower-sugar, Candida-focused diet alongside antifungal treatment. Candida thrives on glucose, so limiting refined carbohydrates and high-sugar foods is commonly recommended. The stricter "Candida diet" (no grains, alcohol, fermented foods) is not robustly validated in controlled trials, so talk to your clinician about what approach makes sense for you.

4. Improving gut motility

Poor gastrointestinal motility is both a cause and a perpetuating factor for SIFO. Two practical supports:

1. Regular aerobic exercise — physical activity helps stimulate gut movement.
2. Spacing meals at least three hours apart — this protects the migrating motor complex, the recurring muscular activity that sweeps the small intestine between meals.

5. Addressing stomach acid

If long-term PPI use is a contributing factor, your doctor may reassess whether acid reduction is still necessary. Some practitioners also suggest betaine HCl to support stomach acid; ask before trying one, particularly if you have ulcers, reflux, or take acid-reducing medications.

The Bottom Line

SIFO is a clinically recognized but often overlooked cause of unexplained GI symptoms. The research suggests roughly 1 in 4 people investigated for unexplained gut symptoms may have it. Because the symptoms overlap with SIBO, IBS, and Candida overgrowth, testing is the only reliable way to know what you're dealing with.

If SIFO is confirmed, the path is straightforward: antifungal medication from your doctor, support through diet and movement, and addressing any underlying risk factors (PPI use, dysmotility). Once the acute phase is behind you, re-establishing a healthy gut microbial community — through diet, fermented foods, and a probiotic matched to your gut data — helps maintain what you've rebuilt.

SIFO FAQ

What is SIFO?

SIFO stands for small intestinal fungal overgrowth — a condition where fungi (most often Candida) are present in excessive numbers in the small intestine, causing symptoms like bloating, gas, belching, nausea, and diarrhea.

What is the difference between SIFO and SIBO?

SIFO is a fungal overgrowth in the small intestine; SIBO is a bacterial overgrowth there. The symptoms overlap considerably, and some people have both conditions simultaneously, which is why testing by a gastroenterologist is the only reliable way to tell them apart.

How is SIFO diagnosed?

SIFO is diagnosed via a small bowel aspirate — fluid collected from the small intestine during an upper endoscopy. A laboratory then checks the sample for elevated fungal counts. At-home stool tests can detect Candida and fungi in the colon but do not diagnose SIFO in the small intestine.

How do doctors treat SIFO?

Once confirmed, the typical first step is a 2–3 week course of antifungal medication (fluconazole or nystatin) prescribed by a physician. Dietary changes (reducing refined sugar), improved gut motility (exercise, spacing meals), and addressing risk factors like long-term PPI use are common supporting steps.

Can probiotics help with SIFO?

Research suggests certain Lactobacillus strains can help support a balanced gut environment, but probiotics are not a treatment for SIFO and have not been shown to clear it in clinical trials. They are a tool for maintaining gut health alongside — not instead of — your doctor's treatment plan.

Is SIFO the same as Candida overgrowth?

SIFO is specifically fungal overgrowth localized to the small intestine; Candida overgrowth is a broader term that can describe too much Candida anywhere in the body (gut, mouth, vaginal canal, skin). Because Candida is the most common fungus in SIFO, there is significant overlap, but the terms are not identical. Learn how to test for Candida overgrowth.

This article is for general education and is not medical advice. It is not intended to diagnose, treat, cure, or prevent any disease. If you have symptoms that concern you, speak with a licensed healthcare provider.

Candida and SIFO often look similar. If you're not sure which you're dealing with, start with the four Candida tests compared.