Differential Effects of Alternate-Day Fasting Versus Daily Calorie Restriction on Insulin Resistance

Objective This study compared the effects of alternate-day fasting (ADF) with those of daily calorie restriction (CR) on body weight and glucoregulatory factors in adults with overweight or obesity and insulin resistance. Methods This secondary analysis examined the data of insulin-resistant individuals (n = 43) who participated in a 12-month study that compared ADF (25% energy needs on "fast days"; 125% energy needs on alternating "feast days") with CR (75% energy needs every day) and a control group regimen. Results In insulin-resistant participants, weight loss was not different between ADF (-8% +/- 2%) and CR (-6% +/- 1%) by month 12, relative to controls (P < 0.0001). Fat mass and BMI decreased (P < 0.05) similarly from ADF and CR. ADF produced greater decreases (P < 0.05) in fasting insulin (-52% +/- 9%) and insulin resistance (-53% +/- 9%) compared with CR (-14% +/- 9%; -17% +/- 11%) and the control regimen by month 12. Lean mass, visceral fat mass, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, blood pressure, C-reactive protein, tumor necrosis factor alpha, and interleukin 6 values remained unchanged. Conclusions These findings suggest that ADF may produce greater reductions in fasting insulin and insulin resistance compared with CR in insulin-resistant participants despite similar decreases in body weight.