Onions are a nutritious vegetable with many health benefits. However, fresh onions are high in FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols), which may be problematic for people with Irritable Bowel Disease (IBD). Eating fermented onions may reduce FODMAP problems and increase the availability of bioactive compounds, especially quercetin. This could help those with IBD enjoy the wonderful flavours of onions in everyday meals, while potentially reducing symptoms of IBD and improving gut health.
Onions are high in fructans, one of the FODMAPs that has been shown to have negative effects on IBD due to its poor absorption in the small intestine, leading to symptoms of Irritable Bowel Syndrome (IBS) in IBD patients.
Fermentation of onions has been shown to enhance onion’s antioxidant activity and the availability of bioactive compounds such as flavonoids and short-chain fatty acids (SCFAs). Diets containing a high content of fermented foods have been shown to increase microbiome diversity and decrease inflammatory activity.
Therefore, fermentation of onion may reduce onion’s FODMAP characteristics and improve IBD. This study aimed to evaluate the effect of fermented onion on gut health in rats induced with IBD. The results showed that fermented onion treatment significantly reduced the mucosal damage by inducing a significant increase in the goblet cell number and the thickness of the mucus layer. Fresh onion, on the other hand, caused a considerable reduction in goblet cells.
In this study, the rats that received the fermented onion showed significantly less intestinal damage compared to the control group that received fresh onion. The fermented onion group also had a higher number of goblet cells, which help to maintain the integrity of the intestinal epithelium by secreting mucin, which contributes to the ongoing replenishing of the intestinal mucus layer. This appears to be the first study that reports the effect of fermented onion on mucus production.
Major immunoglobulins that constitute mucosal immunity are IgA and IgG. IgA is the main antibody generated within the intestines, while IgG is the most prevalent antibody in the peripheral blood. Previous research has shown that patients with IBD had higher levels of serum IgG in the intestinal lumen, as well higher IgA due to impaired mucosal barriers. In this study experiment, IgG and IgA levels in the rats that received fermented onion were significantly reduced, and this group showed improvement in inflammation factors.
The differences in effects between fermented and fresh onions on gut health might be due to the degradation of FODMAP compounds by fermentation, which results in an increase in butyrate in the fermented onion groups, as butyrate has been shown to control oxidative stress in numerous studies. The differences in the chemical compounds of fresh and fermented onions may be another factor that might play a role in the different effects of these two types of onions.
Practice Tips
- Fermented onions are a great way for sufferers of IBD to enjoy the delicious flavour of onion in everyday foods and may also help improve gut health and alleviate symptoms of IBS
- Make a jar of fermented onions and keep in the fridge to add to sandwiches, savoury platters and poke bowls. They make a great accompaniment to all Indian-inspired meals
Reference
Sangpreecha, N.; Chanmuang, S.; Park, K.-H.; Sangar, M.; Sharma, D.; Song, D.; Park, Y.-J.; Sung, H.-M.; Promyo, K.; Ham, K.-S. Effects of Fermented Onion on Gut Health in Dextran Sodium Sulfate (DSS)-Induced Inflammatory Bowel Disease (IBD) Rats. Appl. Sci. 2023, 13, 1590. https://doi.org/10.3390/app13031590
