The goal of this trial is to assess the effect on the quality of life (QoL) of recommending a fat-free diet versus a balanced WHO diet in symptomatic patients with gallstones and in patients undergoing cholecystectomy for gallstone disease. The main question it aims to answer is:

• Is balanced WHO diet as good as low-fat diet in terms of patient reported outcomes when gallstone disease is managed non-operatively (RADIGAL-1) or cholecystectomy is performed (RADIGAL-2)?

A validated QoL questionnaire (Gastrointestinal Quality of Life Index - GIQLI) will be administered both at baseline and during follow-up. Analysis of covariance with ordinary least squares estimation will be applied to estimate between-group differences in GIQLI scores at 3 months (primary endpoint). Patient adherence and the disease-related symptoms occurrence or hospitalizations will also be appraised (secondary endpoint).

Participants presenting with biliary colic or acute cholecystitis (RADIGAL-1) or undergoing cholecystectomy for gallstones (RADIGAL-2) will:

• be randomly assigned to recommending either a fat-free or a balanced WHO diet .
• be contacted via phone call to complete the GIQLI questionnaire and document overall adherence to the diets and secondary outcome events.

This trial examines the impact of diet on adverse events in gallstone disease, representing the first randomized study to focus on this aspect.

Inclusion Criteria (RADIGAL1):

• 18 years old or older
• presenting with biliary colic in the ED or outpatient clinic, with the surgical team deciding to proceed with non-operative treatment (Group 1)
• presenting with acute calculous cholecystitis in the ED, with the surgical team deciding to proceed with non-operative management (Group 2)

Exclusion Criteria (RADIGAL1):

• history of gastrointestinal disease which might affect diet, e.g., inflammatory bowel disease, irritable bowel syndrome, short bowel syndrome
• inability to provide informed consent
• unwillingness to adhere to the recommended diet
• food allergies or intolerances that would prevent following the diet
• dietary habits (e.g., vegetarians, vegans) that preclude adherence to the recommended diet
• gallstone related cholangitis without biliary colic or cholecystitis
• complications from acute pancreatitis, such as pseudocysts, walled off necrosis, among others

Inclusion Criteria (RADIGAL2):

• 18 years old or older
• undergoing uncomplicated cholecystectomy (open or laparoscopic without bile duct exploration) due to a history of biliary colic (Group 1)
• undergoing uncomplicated cholecystectomy (open or laparoscopic without bile duct exploration) due to acute cholecystitis (Group 2)

Exclusion Criteria (RADIGAL2):

• history of gastrointestinal disease which might affect diet, e.g., inflammatory bowel disease, irritable bowel syndrome, short bowel syndrome
• inability to provide informed consent
• unwillingness to adhere to the recommended diet
• food allergies or intolerances that would prevent following the diet - dietary habits (e.g., vegetarians, vegans) that preclude adherence to the recommended diet
• gallstone related cholangitis without biliary colic or cholecystitis
• complications from acute pancreatitis, such as pseudocysts, walled off necrosis, among others
• choledocholithiasis
• complicated cholecystectomy
• patients undergoing subtotal cholecystectomy
• whether primary operation differs from cholecystectomy (e.g., colectomy)
• patients having treated with percutaneous cholecystostomy