- Zonna X et al. The Association Between Crohn’s Disease and Patient Response to Yeast: A Review of the Literature. Gastroenterol Insights 2024; 15(4): 1064-1074. https://doi.org/10.3390/gastroent15040073.
Saccharomyces cerevisiae (baker's or brewer's yeast) is found in many of our foods, especially in baked goods. It has long been suspected of acting as a possible antigen in IBD.
The anti-Saccharomyces cerevisiae antibody is directed against the mannan component of the cell wall of baker's yeast and has been researched in connection with IBD since the early 1990s. At that time, it was first noticed that patients with CD had significantly higher IgG and IgA titres against S. cerevisiae compared to healthy individuals, but also to patients with ulcerative colitis (UC). Since then, ASCA has repeatedly been shown to be a specific marker for CD. However, its low sensitivity again limits its diagnostic value.
Although no correlation has yet been found between elevated antibody titres and sensitivity to yeast in nutrition, CD patients appear to react to yeast-containing foods and benefit from a yeast-free diet, as several studies have shown. In contrast, UC patients tolerated products with yeast without any problems.
Whether yeast even plays a role in the pathogenesis of CD is still controversial. The theory of immune sensitisation has been repeatedly supported in several studies. According to this theory, the yeast antigen mannan leads to strong immune activation in CD patients with a subsequent cascade of increased cytotoxicity, chronic T-cell activation, damage to the mucosal barrier and increased inflammation. Dysregulated T helper (Th) cells, which are falsely activated against various microbial antigens and could therefore contribute to the pathogenesis and severity of CD, could be responsible for this.
ASCA as a potential prognostic marker is another exciting area of research. Some studies suggest that the immune response to yeast may have significant potential for predicting the onset and progression of Crohn's disease. For example, elevated antibody titres have been associated with disease severity, the likelihood of complications and the need for surgical intervention. It is therefore possible that ASCA could become relevant for risk stratification in the future and help with treatment decisions.
Finally, research into the intestinal microbiome in IBD has been in full swing for some time. Here too, yeast and their antigens could lead to substantial changes. For example, differences in the composition of the microbiome have been found in ASCA-positive and -negative patients. Significant differences were also found in the microbiome of CD and UC patients. According to some authors, these differences could also have an aetiological and phenotypic impact.
After several decades of research, many questions about nutrition and its role in chronic inflammatory bowel diseases such as Crohn's disease and ulcerative colitis remain unanswered. However, there is growing evidence that yeast fungi and the immune response they induce play an important role. The question is whether and when this will have concrete consequences for diagnostics, therapy and prognosis.