From the Guidelines
Fasting can be a beneficial practice for overall health when done properly, with potential benefits including improved insulin sensitivity, reduced inflammation, and weight management, as supported by recent studies such as 1 and 1. To practice fasting safely, it is essential to start with intermittent fasting approaches, such as the 16:8 method or the 5:2 method, and gradually allow the body to adapt over several weeks.
- Stay well-hydrated during fasting periods by drinking water, black coffee, or unsweetened tea.
- When not fasting, focus on nutrient-dense whole foods, including lean proteins, healthy fats, complex carbohydrates, fruits, and vegetables.
- Take any prescribed medications as directed by the doctor, as fasting may affect how medications work.
- People with certain health conditions, including diabetes, eating disorders, pregnancy, or those who are underweight, should avoid fasting without medical supervision.
- Break fasts gently with small, easily digestible meals rather than large feasts. The most recent and highest quality study, 1, highlights the importance of individualized and culturally sensitive treatment for people with diabetes who fast, including education on glucose checking, medication adjustment, and meal choices pre- and post-fast. It is crucial to be aware of potential risks, such as dehydration and thrombosis, especially in hot and humid climates or among individuals who perform hard physical labor, as noted in 1. Overall, fasting can be a valuable practice for improving overall health, but it is essential to approach it mindfully and consistently, with proper guidance and precautions.
From the Research
Effects of Fasting on Overall Health
- Fasting has been shown to produce mild to moderate weight loss (1-8% from baseline) and consistent reductions in energy intake (10-30% from baseline) 2
- Intermittent fasting regimens, such as alternate-day fasting (ADF), the 5:2 diet, and time-restricted eating (TRE), may benefit cardiometabolic health by decreasing blood pressure, insulin resistance, and oxidative stress 2, 3
- Fasting has also been linked to improved appetite regulation and favorable changes in the diversity of the gut microbiome, although evidence for these effects is limited 2, 4
- The potential health benefits of fasting can be related to both the acute food restriction and chronic influence of weight loss, and may include increased life and health span, enhanced intrinsic defences against oxidative and metabolic stresses, improved cognition, and a decrease in cardiovascular risk 5, 4, 6
Metabolic Effects of Fasting
- Modified fasting regimens appear to promote weight loss and may improve metabolic health by influencing metabolic regulation via effects on circadian biology, the gut microbiome, and modifiable lifestyle behaviors such as sleep 3
- Fasting can lead to a switch from glucose to fat and ketones as an energy source, which can have beneficial effects on cognition and appetite regulation 4
- Intermittent fasting has been shown to have long-term benefits for overall and specific organismal health and longevity, including extended longevity, weight loss, and counteracting various disease conditions 6
Safety and Efficacy of Fasting
- Intermittent fasting is generally safe and does not result in energy level disturbances or increased disordered eating behaviors 2
- Fasting can be an effective strategy for weight loss and maintenance, particularly when combined with other lifestyle changes such as a healthy diet and regular exercise 5, 3
- Different protocols of intermittent fasting, including intermittent fasting, periodic fasting, or long-term fasting, can be used to achieve health benefits, and the choice of protocol may depend on individual preferences and needs 4