Background and aims: Lifestyle factors could influence the development of metabolic dysfunction–associated steatotic liver disease (MASLD). However, there is a lack of data including the consumption of ultra-processed foods (UPF) within the broad field of steatotic liver disease. Methods: Dietary intake and physical activity were assessed using standardized questionnaires in patients with MASLD, ALD and healthy controls. Liver disease severity was quantified by transient elastography and liver histology. Results: One hundred and fifty-two patients with MASLD were recruited and compared with 95 patients with ALD and 31 controls. Patients with MASLD consume significantly less total calories than patients with ALD (1620 vs. 2290 kcal/day, p < 0.0001), primarily due to lower alcohol intake, despite a higher body mass index. ALD patients consume lower proportions of proteins, lipids, carbohydrates, and dietary fibres than MASLD and control groups. Fibre intake is higher in the control group compared with the MASLD and ALD groups. In the biopsied MASLD subgroup, significant fibrosis is associated with a lower fibre intake (15 vs. 19 g/day, p = 0.03). No differences in NOVA category distribution are observed between MASLD and control groups, and UPF intake is not associated with liver histological severity. Controls devote a greater proportion of leisure-time physical activity (54% vs. 11% in MASLD and 17% in ALD, p < 0.0001). Conclusions: Patients with MASLD and ALD exhibit lower dietary fibre intake and reduced leisure-time physical activity compared with controls. Fibre intake, but not UPF consumption, is associated with fibrosis severity in MASLD.