Guest blog by Lillian Craggs-Dino, DHA, RDN, LDN, CLT, FASMBS-IH Many people turn to intermittent fasting (IF) as a tool for weight management and metabolic health. It has been praised for its potential to support weight loss, regulate blood sugar levels, and potentially even promote longevity. But for individuals who have undergone bariatric surgery, questions often arise: Is intermittent fasting safe? Can it fit within a bariatric lifestyle? This blog explores what IF is, its potential benefits, and the key considerations for bariatric patients who may be curious about adopting this eating pattern. Understanding the Bariatric Diet Metabolic and bariatric surgery provides a restrictive tool that helps patients stay on track with their diet. The bariatric diet prioritizes protein, fluids, and essential vitamins and minerals to support recovery and long-term success. Bariatric dietitians also encourage specific eating habits that promote positive outcomes. Some programs recommend several small meals throughout the day, while others suggest eating three structured meals with no snacks if protein needs are met. There is no single approach that works for everyone—success depends on individual needs, tolerance, and surgical procedure. What Is Intermittent Fasting? Intermittent fasting is a time-restricted eating pattern that cycles between periods of eating and fasting. While there’s no universal definition, all IF protocols share the goal of reducing calorie intake by limiting eating windows. The approach became popular in the late 1990s and 2000s for its reported benefits in weight loss, blood sugar regulation, and cancer prevention. Research has shown that IF can also enhance autophagy, the body’s natural process of cleaning out damaged cells to support healthy function and energy balance.1,2,3,4 Common IF schedules include: 16:8 method: 16 hours of fasting, 8 hours of eating 18:6 method: 18 hours of fasting, 6 hours of eating 5:2 method: Two days per week of reduced-calorie intake Alternate-day fasting: Fasting every other day More details on different IF protocols can be found in the table below. Can Bariatric Surgery Patients Follow Intermittent Fasting? The short answer is yes, but with important precautions. Patients who have undergone bariatric surgery can follow an intermittent fasting plan, as long as they continue to meet the nutritional priorities of the bariatric diet, including: Adequate protein intake Consistent hydration Lifelong vitamin and mineral supplementation Because of the smaller stomach capacity after surgery, patients may find it challenging to consume enough nutrients during shortened eating windows. Dehydration is one of the most common risks. Additionally, limiting eating hours may make it harder to reach daily protein and calorie goals, especially early after surgery. Key Precautions and Tips Before starting an intermittent fasting regimen, bariatric patients should consult their healthcare team, including a registered dietitian nutritionist (RDN). Professional guidance ensures that IF is approached safely and effectively, while maintaining adequate nutrient intake. Patients interested in trying IF should: Begin gradually and monitor how their body responds Track protein and fluid intake, as well as energy levels Watch for signs of fatigue or dehydration Reevaluate regularly with their bariatric care team When done carefully, intermittent fasting may offer flexibility and metabolic benefits for some bariatric patients, but it must always support, not replace, the foundation of a balanced bariatric diet. Common Intermittent Fasting Protocols5 Protocol Frequency Duration Comment Alternate day fast (ADF) Every other day 24 hours Rotate a fasting day and an eating day; calorie-free beverages allowed on fasting days; some regimens show a 75% calorie reduction on fast days; cons: difficult to follow and may promote binge eating Time-restricted Every day 16:8, 18:6, and 20:4 Pros: easier for those who don't eat breakfast or snack after dinner Modified fast 2-3 times per week Small amounts of food allowed on fast days; defined as either 20-25% total calorie needs or 400-700 calorie/day. The 5:2 or 4:3 is included here: fasting for 2 days and then 5 days eating according to regular pattern (or fasting for 3 days and eating for 4) Weekly one-day fasting Once per week 24 hours Water only on fasting day 10-day juice fast Irregular frequency 240 hours No solid food; fruit juices and broth allowed Conclusion Intermittent fasting can be a viable eating pattern for some individuals after metabolic and bariatric surgery, but it’s not for everyone. Success depends on maintaining protein, hydration, and micronutrient intake while monitoring how your body responds. Always work closely with your bariatric team and RDN to ensure any dietary changes support your long-term weight management and health goals. References 1. Barnosky AR et al. Transl Res. 2014;164(4):302-311.2. Carter S et al. JAMA Netw Open. 2018;1(3):e180756.3. Carter S et al. Diabetes Res Clin Pract. 2019;151:11-19.4. Wolska W et al. Int J Mol Sci. 2025;26(10):4742.5. Grajower MM et al. Nutrients. 2019;11(4):873.