Effect of Intermittent Fasting versus Continuous Caloric Restriction on Body Weight and Metabolic Parameters in Adults with Overweight or Obesity: A Narrative Review

Abstract Obesity and type 2 diabetes have reached epidemic proportions worldwide, including the Middle East and North Africa region. Intermittent fasting (IF) has been increasingly used to manage overweight/obesity and its metabolic complications. Physiologically, IF shifts the body's metabolism into ketosis (the metabolic switch) and induces cellular changes, which have a theoretical benefit over and above continuous caloric restriction (CCR). In this narrative overview of IF, the focus is on summarizing studies that compare IF to CCR in adults with overweight or obesity. The most commonly practiced types of IF (5:2, the alternate day fast, and the time-restricted eating) were included. Nine studies of 1-year duration or longer, with weight loss as the primary outcome, were summarized. The effect on body weight and improved metabolic parameters such as blood pressure, glycemic indicators, and lipid profile are described. Overall, IF was well tolerated and effective for weight loss in a manner comparable to CCR. The benefits were similar among adults with type 2 diabetes. There were no additional metabolic effects or benefits over and above CCR. However, more studies are needed to address specific details of IF, such as the type and timing of fasting and its application to different populations. In conclusion, IF is safe and beneficial for weight loss in adults with overweight/obesity with or without diabetes. It can be used as an alternative to CCR.