Is MASLD Not Just a Liver Disease? Bidirectional Gut–Liver Crosstalk as a Driver of Chronic Liver Disease

Irritable bowel syndrome (IBS) and metabolic dysfunction-associated steatotic liver disease (MASLD) are two of the most common gastroenterological conditions worldwide. Traditionally viewed as unrelated, with one serving a canonical functional role and the other a purely metabolic function, these two processes have recently been linked by compelling evidence, challenging their traditional segregation and pointing to a significant, biologically relevant association. This review aims to evaluate the current evidence for a potential causal contribution of IBS to hepatic steatosis, critically examining the proposed pathophysiological mechanisms via the gut–liver axis while acknowledging that the available data are primarily observational. Notably, epidemiological studies demonstrate a 1.4–2.0-fold increased association between IBS and MASLD, independent of obesity and metabolic syndrome, though causality remains to be established. The primary mechanism is increased intestinal permeability (“leaky gut”) leading to endotoxemia, activation of hepatic toll-like receptor 4 (TLR4) receptors, and subsequent de novo lipogenesis. The relationship is bidirectional, with steatosis also worsening gut barrier function. Therefore, we highlight emerging evidence suggesting that irritable bowel syndrome, particularly the diarrhea-predominant subtype (IBS-D), may contribute to hepatic steatosis through plausible biological mechanisms, though direct causal evidence in humans remains limited. Accordingly, routine screening for metabolic dysfunction-associated steatotic liver disease (MASLD) may be warranted in patients with long-standing IBS-D.