Non-alcoholic fatty liver disease in irritable bowel syndrome: More than a coincidence?

Table 1 Summarizes the literature on the co-existing prevalence of irritable bowel syndrome and non-alcoholic fatty liver disease to date

Author	Population studied	Study design	No. patients	Criteria for IBS diagnosis	IBS subtypes	Criteria for NAFLD diagnosis	Prevalence of NAFLD in IBS/ IBS in NAFLD	Outcomes
Hasanain et al[15]	IBS	Cross sectional study	100 patients with IBS	Rome III	IBS-C: 45%; IBS-D: 23%; IBS-M: 32%,	Ultrasound; No history of alcohol exposure; No exposure to steatogenic medications; Negative viral screen	74% of those with IBS had co-existing NAFLD	Moderate/severe NAFLD significantly associated with moderate/severe IBS (OR: 2.4, 95%CI: 1.3-62.7, P = 0.026)
Shin et al[16]	Healthy individuals via NHANES	Cross sectional study	2345 patients with IBS	Rome IV	IBS-C: 1023; IBS-D: 1322	Raised ALT or AST; Absence of excessive alcohol; Negative viral hepatitis screen	Prevalence of NAFLD in IBS-D: 12.9% (95%CI: 9.8-15.9); IBS-C: 9.0% (95%CI: 7.0-11.0)	NAFLD associated with diarrhoea vs normal bowel pattern (OR: 1.340, 95%CI: 1.007-1.784) and constipation (OR: 1.445, 95%CI: 1.028-2.031)
Arasteh et al[17]	IBS	Cohort study	1067 patients with IBS	Rome IV	IBS-D: 57 (5.3%); IBS-C: 380 (35.6%); IBS-U: 630 (59%)	Not documented	3.7%	Liver disease not associated with IBS (Coefficient: 0.26, OR: 1.30, 95%CI: 0.92-1.82)
Lee et al[19]	IBS vs control	Retrospective, cross sectional, case control study	83 IBS patients; 260 age and sex matched control	Rome III	IBS-C: 14.8%; IBS-D: 49.4%; IBS-M: 31.3%; IBS-U: 4.5%	Investigated raised ALT, GGT, AST and features of metabolic syndrome	16.9% of IBS patients had raised ALT; 24.1% had raised GGT	Significantly higher ALT in patients with IBS (16.9% vs 7.7%; P = 0.015); Significantly higher GGT in patients with IBS (24.1% vs 11.5%; P = 0.037); Significantly higher prevalence of metabolic syndrome in patients with IBS (32.5% vs 12.7%; P < 0.001)
Sarmini et al[73]	IBS vs control	Observational study	637942	Clinical diagnosis	Not documented	Not documented	Not available	Patients with IBS significantly more likely to develop NAFLD compared to non-IBS group (OR: 3.204, 95%CI: 3.130-3.279, P < 0.001)
Singh et al[24]	NAFLD	Retrospective analysis	632	Clinical diagnosis	Not documented	Ultrasound; Alcohol consumption < 20 g/d; Normal aetiological liver screen	186 (29.4%) patients with NAFLD had clinical diagnosis of IBS	IBS symptoms are highly prevalent in those with NAFLD
Jones-Pauley et al[22]	NAFLD	Cross-sectional study	130	Rome IV	Not documented	Not documented	38 (29.2%) patients with NAFLD met Rome IV IBS criteria	High prevalence of IBS in patients with NAFLD; Significant increase in prevalence of depression (18.4% vs 5.4%, P = 0.01) and anxiety (31.6% vs 9.8%, P = 0.002) in those with co-existing IBS compared to those with NAFLD without IBS

IBS: Irritable bowel syndrome; NAFLD: Non-alcoholic fatty liver disease; IBS-C: Constipation predominant IBS; IBS-D: Diarrhoea predominant IBS; IBS-M: Mixed IBS; IBS-U: Unsubtyped IBS; OR: Odds ratio; CI: Cumulative incidence; ALT: Alanine aminotransferase; AST: Aspartate aminotransferase; GGT: Gamma-glutamyl transferase.