Intestinal Yeast Overgrowth – Driver of Multiple Symptoms

Jonathan Vellinga, MD -

Intestinal Yeast Overgrowth

There are many different types of yeast, including yeasts that help create bread and beer! They are types of fungi that mostly live in harmonious, mutually beneficial relationships with bacteria, plants, and humans (1). Yeasts, along with bacteria, viruses, and parasites, are part of the millions of microscopic organisms that humans host. Yeasts are a subcategory of fungus along with mushrooms and molds, and if someone is not being specific may use the terms “yeast” and “fungus” interchangeably. There are about 1,500 species of yeast, and they can have unique characteristics depending on their species. Some species of yeast, such as Candida, can create health problems by overgrowing in the human body.

The idea of yeast creating health problems has not always been accepted or popular. It’s been known for a long time that yeast dwells in and on humans, but it was thought that its presence was always benign. Then, in 1984, William G. Crook, M.D., wrote the book “The Yeast Connection,” outlining the symptoms of yeast overgrowth, bringing the condition to the public’s attention. It has remained a classic read for a good foundational knowledge of the condition, with new editions and cookbooks added over the years.

Candida albicans (C. albicans) – Yeast Species of Interest

Candida albicans is a species of yeast that is often the culprit in an overgrowth situation. It is a single-celled fungus that thrives in the human body and is often simply called “yeast” or “candida.” C. albicans lives on our skin and within us, mostly living in the linings of our gastrointestinal tract (mouth, throat, esophagus, stomach, small and large intestines, rectum), but also dwelling in the reproductive tracts (2). It is estimated that roughly half of adults have C. albicans in them without having negative symptoms. They divide easily, but the cell walls of yeast are very tough and difficult to penetrate, making them very hardy and resistant to medications. Oddly, C. albicans is known to produce a toxin that can damage the host’s cells (3).

Double Trouble – This Yeast Can Take Two Forms

Not only can C. albicans take the form of a cell, but they can also grow filamentous cells, tendrils that can grow out like a vine. These tendrils, called “hyphae,” can grow through groups of cells that form a tissue, such as intestinal linings. In the lab, they can grow through tissues as fast as 22 hours (4). Not surprisingly, the hyphae form of the yeast is considered “pathogenic,” meaning it can cause a health issue or disease. In severe (but rare) cases, C. albicans pierces the walls of the large intestine with the hyphae, causing an acute health crisis (5).

C. albicans can also become part of a biofilm or help create one. A biofilm is a tight mat of microorganisms that form together as a form of protection, which can be beneficial or pathogenic, as not all biofilms are dangerous to humans. In the intestine, C. albicans can help form a biofilm with their hyphae, which overlap like a basket weave and form a structure to which other microorganisms can also join. This biofilm is very difficult to eradicate once grown, as the microorganisms combine their protective capabilities, making it difficult for medications to penetrate the mass (6). This sets the yeast up to live a long time, creating a chronic condition of gut flora imbalance. They can clog up the large intestine, making water reclamation from the wastes more difficult.


The overgrowth of any of the Candida family of yeasts is called “candidiasis.” The symptoms may vary depending on where the overgrowth occurs. It is always our goal to find the root cause of illness, and we find that the overgrowth of Candida in the intestines is often the root cause of a wide variety of symptoms. If the underlying Candida overgrowth is not addressed, the symptoms can persist and worsen over time until the patient is seriously ill. The longer the condition persists, the harder it becomes to eradicate.

Yeast Overgrowth in the Small Intestines (SIFO - Small Intestine Fungal Overgrowth)

Many people are already familiar with SIBO – Small Intestine Bacterial Overgrowth. However, bacteria are not the only thing that can negatively impact the small intestine and disrupt the digestive tract. Normally the small intestine resists being populated by microorganisms. The small intestine naturally has an environment that discourages microorganisms from growing in there. However, there are a variety of conditions that make it more likely for funguses such as Candida yeasts to not only survive but thrive in the small intestine and start causing problems. The mere presence of GI symptoms can be an indication of an issue. There have been a few studies that showed that about 25% of people with “unexplained GI symptoms” actually had SIFO (7).