Rationale:
There are no established guidelines or high-quality evidence supporting the widespread use of a fat-free diet in patients with cholecystitis or biliary colic, either as part of conservative treatment or postoperatively. This is the first clinical trial to assess the role of a more flexible diet, World Health Organization (WHO) diet, characterized by total fat <30% of daily energy intake and limited saturated fats (<10%), as an alternative to the traditionally prescribed fat-free diet, which contains <5% of total daily energy from fat, in symptomatic gallstone disease.

Methods:
Patients presenting with biliary colic or acute cholecystitis(RADIGAL-1), or undergoing cholecystectomy for gallstones(RADIGAL-2), are randomized to receive recommendations for either a fat-free diet or a WHO-diet. A follow-up at 3 months evaluates adherence, adverse events, and quality of life using the validated Gastrointestinal Quality of Life Index (GIQLI). Based on sample size calculations, recruitment targets are 136 patients for RADIGAL-1 and 106 for RADIGAL-2.

Results:
To date, 71.3% of the planned recruitment target for RADIGAL-1 and 92.5% of RADIGAL-2 participants have completed the 3-month follow-up. In RADIGAL-1, 88.7% achieved full compliance, 7.2% adhered for more than 50% of the time, and 2.1% adhered for less than 50% of the time. In RADIGAL-2, the compliance rates were similar: 89.8%, 7.1%, and 3.1%, respectively. The main reason for less than full adherence was that participants did not experience any symptoms (83%). Rates of adverse events were similar between diet groups (RADIGAL-1: 20.8% vs.22.4%, p=0.8; RADIGAL-2: 12.5% vs.18.4%, p=0.4), as were hospital readmissions (RADIGAL-1: 20.4% vs.12.5%,p=0.4; RADIGAL-2: 4.1% vs.4.2%,p=0.9). A decrease in QoL at 3 months was more frequent in the fat-free group (14.9% vs.4.2%,p=0.4 in RADIGAL-1; 6.1% vs.12.5%,p=0.4 in RADIGAL-2). At 3 months, GIQLI scores were similar between diet arms in both trials (RADIGAL-1: 136.4 ± 6.8 vs.136.3 ± 6.7; mean difference−0.1, 95% CI−2.8 to 2.6; p=0.9; RADIGAL-2: 134.8 ±10.7 vs.135.8 ±11.9; mean difference 1.0, 95% CI−3.6 to 5.6; p=0.7).

Conclusion:
Preliminary results suggest that the WHO diet is not inferior to the empirically prescribed fat-free diet in the management of symptomatic gallstone disease, regarding biliary adverse events and quality of life.