The 5:2 diet, an eating plan characterized by 5 days of unrestricted eating and 2 days of fasting per week, is effective for weight reduction and reducing the risk for cardiovascular disease in patients with overweight and obesity, according to a systematic review and meta-analysis published in the International Journal of Endocrinology.

“Although fasting may cause mild symptoms, none of the articles reported serious adverse effects of the 5:2 diet, suggesting that this diet is safe and feasible,” wrote corresponding author Chunli Piao, MD, and colleagues.

The review and meta-analysis included 20 randomized controlled trials that studied the effects of the 5:2 diet in 1,393 participants with overweight and obesity in North America, Europe, Asia, and Oceania. Among participants, 689 were in intervention groups and 704 were in control groups.

The 5:2 diet significantly reduced body weight, BMI, waist circumference, body fat percentage, hip circumference, fat mass, low-density lipoprotein (LDL) cholesterol, and systolic blood pressure (SBP) relative to findings in the control group, according to the meta-analysis. Fat-free mass of which muscle is the main component also significantly decreased with the 5:2 diet.

“This may be due to muscle loss through mechanisms such as energy deficit, metabolic adaptation, inadequate protein intake, or reduced physical activity,” researchers wrote.

In addition, people of middle age had significantly more success losing weight and fat compared with younger and older age groups. The authors wrote that this may be due to the fact that middle-aged people have a higher willingness to lose weight and are better able to participate in fasting programs.

Common physical symptoms associated with the 5:2 diet included fatigue, feeling cold, headache, dizziness, and constipation. Common psychologic symptoms were difficulty concentrating, bad temper, and sleep disturbances. Side effects were mild, though, and resolved after fasting. The researchers emphasized that the 5:2 diet is not suitable for all people, and even mild side effects can be harmful to vulnerable groups, such as older adults or people with frailty.

“The patient’s physical condition during the fasting period should be monitored,” researchers advised, “and timely adjustments should be made accordingly.”