Medically Safe Rate of Weight Loss for the Treatment of Obesity: a Guideline Based on Risk of Gallstone Formation

Objective: Currently recommended rates of weight loss for obese persons are not based on demonstrated health risks. The authors attempt to determine a medically safe rate of weight loss based on currently available data on the risk of gallstone formation during active weight loss.

Methods: All prospective studies published in the English language on the formation of gallstones in obese persons during active weight loss were reviewed and evaluated. A statistical analysis was performed using studies of at least 4 weeks' duration that included information on diet composition, rates of weight loss, length of follow-up, and incidence of gallstone formation. A statistical model was fit to the data from the studies that met the criteria.

Results: Nine subject groups derived from five published reports met the criteria for inclusion in the analysis. When the results of these groups were evaluated statistically, a curvilinear relationship between incidence of gallstone formation and rate of weight loss was demonstrated. The relationship was best described by an exponential regression curve, with an adjusted r2 of 0.98 and a dramatically increasing risk of gallstone formation at rates of weight loss above 1.5 kg per week.

Conclusion: Risk of gallstone formation in obese persons during active weight loss seems to increase in an exponential fashion. The data suggest that rates of weight loss should not exceed an average of 1.5 kg per week.