Intermittent fasting (IF) regimens have gained considerable popularity in recent years, as some people find these diets easier to follow than traditional calorie restriction (CR) approaches. IF involves restricting energy intake on 1-3 d/wk, and eating freely on the nonrestriction days. Alternate day fasting (ADF) is a subclass of IF, which consists of a "fast day" (75% energy restriction) alternating with a "feed day" (ad libitum food consumption). Recent findings suggest that IF and ADF are equally as effective as CR for weight loss and cardioprotection. What remains unclear, however, is whether IF/ADF elicits comparable improvements in diabetes risk indicators, when compared with CR. Accordingly, the goal of this review was to compare the effects of IF and ADF with daily CR on body weight, fasting glucose, fasting insulin, and insulin sensitivity in overweight and obese adults. Results reveal superior decreases in body weight by CR vs IF/ADF regimens, yet comparable reductions in visceral fat mass, fasting insulin, and insulin resistance. None of the interventions produced clinically meaningful reductions in glucose concentrations. Taken together, these preliminary findings show promise for the use of IF and ADF as alternatives to CR for weight loss and type 2 diabetes risk reduction in overweight and obese populations, but more research is required before solid conclusions can be reached.
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