Alternate Day Fasting and the 5:2 Diet: Effects on Body Weight and Metabolic Disease Risk Factors

The goal of this review is to summarize the effects of alternate-day fasting (ADF; 0–500 kcal fast day, alternated with an ad libitum intake feast day) and the 5:2 diet (2 fast days per week, 5 ad libitum feast days) on body weight and markers of cardiometabolic health in humans. Results reveal that ADF and 5:2 can produce clinically significant weight loss in individuals with overweight or obesity. Clinical trial evidence shows that these diets produce reductions in energy intake of approximately 10 to 30% and mild to moderate weight loss (1–8% from baseline). These regimens may lower coronary heart disease and diabetes risk by decreasing blood pressure, insulin resistance, and oxidative stress. LDL cholesterol and triglyceride levels are also reduced, but improvements in these lipid parameters are not consistent. Favorable changes in the diversity and overall composition of the gut microbiome have also been demonstrated, but more studies will be needed to confirm these findings. These diets do not produce deleterious changes in sleep, reproductive hormones, thyroid hormones, RMR, eating disorder symptoms, or diet quality. While these preliminary data offer promise for the use of ADF and the 5:2 diet as an alternative option to daily calorie restriction for treating obesity and metabolic disturbances, more research will be needed to provide crucial clinical evidence to support the use of fasting in clinical treatment guidelines.