Chlorella, a green freshwater microalga, has been explored for its potential benefits in gastrointestinal health, including colitis. Preclinical studies, mostly in animal models, suggest that chlorella supplementation may exert anti-inflammatory effects in the colon. For example, rodent studies have shown that chlorella extracts can reduce colonic inflammation, decrease pro-inflammatory cytokines (such as TNF-α and IL-6), and improve antioxidant status in experimentally induced colitis models. These effects are thought to be due to chlorella's bioactive compounds, including chlorophyll, polysaccharides, and antioxidants, which may help modulate immune responses and oxidative stress in the gut.

However, direct evidence in human subjects with colitis (such as ulcerative colitis or Crohn's disease) is very limited. Only a few small clinical trials have investigated chlorella’s effects on broader gastrointestinal symptoms or immune markers, and these studies have typically involved healthy subjects or those with irritable bowel syndrome, not specifically colitis. There is currently insufficient high-quality clinical data to conclusively recommend chlorella as a treatment for colitis in humans. Most reviews and guidelines do not include chlorella among evidence-based interventions for inflammatory bowel diseases.

In summary, while preliminary scientific evidence from animal models suggests a potential benefit for colitis, the lack of robust human clinical trials means the scientific evidence is weak (rated 2/5). More research—especially well-designed human studies—is needed to determine chlorella’s efficacy and safety for colitis.