From the Guidelines
Fasting for 3-4 days for weight loss is not recommended without medical supervision due to potential risks of muscle loss, nutritional deficiencies, electrolyte imbalances, and metabolic slowdown. While short-term fasting can lead to quick weight loss, much of this is water weight that returns when normal eating resumes [ 1 ]. Extended fasts can also trigger disordered eating patterns in susceptible individuals. For sustainable weight loss, a better approach is moderate calorie reduction (500-750 calories below maintenance) combined with regular physical activity.
Key Considerations
- Intermittent fasting methods like 16:8 (16 hours fasting, 8 hours eating) or 5:2 (5 normal days, 2 very low calorie days) tend to be safer alternatives if you're interested in fasting approaches [ 1 ].
- Anyone with medical conditions, taking medications, pregnant, or with a history of eating disorders should absolutely consult a healthcare provider before attempting any fast.
- Sustainable lifestyle changes that you can maintain long-term will always be more effective for lasting weight management than extreme short-term measures [ 1 ].
Important Evidence
- A study of alternate-day fasting in adults with NAFLD led to weight loss and improvement in lipid parameters, but no change in liver stiffness by transient elastography [ 1 ].
- The American Heart Association recommends matching intake of total energy (calories) to overall energy needs and achieving a level of physical activity that matches (for weight maintenance) or exceeds (for weight loss) energy intake [ 1 ].
From the Research
Health Effects of 3 or 4 Day Fasts for Weight Loss
- The health effects of 3 or 4 day fasts for weight loss are not directly addressed in the provided studies, which focus on intermittent fasting protocols such as alternate-day fasting, whole-day fasting, and time-restricted feeding 2, 3, 4.
- However, a study on twice-weekly 36-hour intermittent fasting found that this protocol can attenuate hunger, increase ß-hydroxybutyrate, and maintain weight loss 5.
- Another study compared intermittent fasting one day versus two days per week, matched for total energy intake and expenditure, and found that two days of intermittent fasting per week resulted in greater reductions in body weight and waist circumference 6.
Safety and Efficacy of Intermittent Fasting
- Intermittent fasting has been shown to be an effective strategy for weight loss, with studies demonstrating significant reductions in body weight, body fat, and improvements in clinical health markers 2, 3, 4, 6.
- However, the safety and efficacy of intermittent fasting depend on various factors, including the specific protocol used, individual health status, and nutritional adequacy 3.
- It is essential to consult with a healthcare professional before starting any fasting regimen, especially for individuals with underlying health conditions or nutritional deficiencies.
Considerations for Weight Loss
- Weight loss is a complex process, and there is no one-size-fits-all approach 2.
- Intermittent fasting may be a useful dietary strategy for weight loss, but it is crucial to consider individual factors, such as lifestyle, preferences, and health status, when choosing a weight loss approach 2, 3.
- A well-planned and balanced diet, combined with regular physical activity and a healthy lifestyle, is essential for achieving and maintaining weight loss 4, 6.