Intermittent fasting: Is it right for you?

The practice of intermittent fasting has become quite popular in diet culture. You might have heard it helps with weight loss and improves certain health markers. But does it really live up to all the hype? Intermittent fasting has been beneficial for many people, but for others—especially when fuel for performance is a consideration—it might do more harm than good.

What is intermittent fasting?

Fasting itself is not a new practice. In fact, it’s a common tradition in various religions. Intermittent fasting, however, is a dietary practice that involves abstaining from food for certain periods of time to improve health. It is practiced in many ways, but the most common methods are time-restricted feeding and alternate-day fasting.

Time-restricted feeding involves fasting each day for an extended period, usually 16–20 hours. This leaves a 4–8 hour window in which you can consume food. Alternate-day fasting involves eating normally one day, followed by a day of little to no intake of food. Fasting days in alternate-day fasting can range from 2–4 days each week. An example of this is the 5:2 diet, which involves 5 days of normal eating and 2 nonconsecutive days of fasting each week.

Benefits of intermittent fasting

You’ve probably heard about some of the benefits of intermittent fasting. The available research indicates that weight loss is the most common outcome. Many people also experience improvements in certain health markers such as blood sugar and cholesterol levels. Another proposed benefit is increased longevity.

For example, if you practice time-restricted feeding and only eat within the hours of 1100 to 1900, you might find this an easy way to reduce your calorie intake, especially if you’re someone who tends to eat a lot at night. This is especially true if you like sweets and treats right before bed. Similarly with alternate-day fasting, many people don’t make up for what they didn’t eat on their fasting days, which ultimately creates a calorie deficit.

Because intermittent fasting reduces your calorie intake, it can help support weight loss. By itself, weight loss can help improve various markers of health, which is why the practice has been beneficial for so many. However, keep in mind that if you follow a balanced, calorie-restricted diet, you can also experience the same benefits. The outcome of intermittent fasting is often no different when compared to a reduced-calorie diet that doesn’t limit feeding times.

What else to consider

At this time, the long-term effects of intermittent fasting are still unknown. It is uncertain whether this eating regimen can be practiced safely over time and, if it can, what the benefits are. Short-term intermittent fasting works wonderfully for some people, but not everyone experiences the benefits. If you’re curious how it might work for you, keep a food diary to track how you normally eat compared to what you eat during intermittent fasting.

If you try intermittent fasting, also consider the types of foods you eat. If you eat nutrient-dense, high-quality foods, you’re likely to benefit more than someone who feasts on empty calories and low-nutrient foods.

The downside to intermittent fasting

Many people are successful with intermittent fasting, but for others it can be too restrictive. A common complaint is managing hunger, which can be problematic for those prone to overeating. For example, if you don’t start eating until noon each day, you might find yourself so ravenous by then that you end up gorging yourself when your eating window begins.

Even if you don’t experience overwhelming hunger, you could experience other side effects such as headaches, moodiness, or the inability to focus. These are all side effects of not fueling your body properly. It might also be difficult to consume the wide variety of foods and nutrients your body needs each day within a short period of time.

Intermittent fasting also can interfere with your social life. You might find it difficult to plan events with family and friends that take place while you’re trying to adhere to a particular fasting regimen.

Effects on athletic performance

If you participate in regular exercise, the most significant downside to intermittent fasting is its effect on athletic performance. Many athletes who try intermittent fasting find their workouts suffer because they need regular meals and snacks throughout the day to provide fuel for exercise and recovery. The timing of meals and snacks around workouts is key to promote optimal performance. It can be difficult to push yourself during exercise when you haven’t eaten. Plus, delaying food after exercise can slow your recovery.

If you want to try intermittent fasting, consider exercising during your feeding window, so you can eat before and after activity. Fasting or not, you might want to review HPRC’s article on nutrient timing to get the most out of your workouts and optimize recovery.

When intermittent fasting might not be safe

If you’re among those in a few special groups, you should avoid intermittent fasting because it might pose significant health risks such as malnutrition or poor growth. These groups include:

  • Growing children and adolescents
  • Pregnant and breastfeeding women
  • Anyone with a history of an eating disorder
  • Diabetics
  • The elderly

Intermittent fasting and military wellness

Intermittent fasting is a popular dietary practice that has helped many people lose weight and improve their health. Although it’s beneficial for many, others don’t experience the same positive outcomes. Military Service Members might find it particularly difficult to practice intermittent fasting when events such as training exercises and deployments affect their eating schedule. Restricting food intake might do more harm than good in these situations, especially when optimal physical and cognitive performance is required. A visit with a Registered Dietitian can help you decide if intermittent fasting is appropriate or if other nutrition and weight-loss strategies might be better options.

CHAMP wants to know:
How useful was the information in this article?


plus icon minus icon

Academy of Nutrition and Dietetics, American College of Sports Medicine, & Dietitians of Canada. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. 116(3), 501–528. doi:10.1016/j.jand.2015.12006

Anonymous. Diet Review: Intermittent fasting for weight loss.   Retrieved 11 December 2020 from

Anonymous. (2019). Not so fast: Pros and cons of the newest diet trend.   Retrieved 11 December 2020 from

Anonymous. (2020). 5 questions about intermittent fasting.   Retrieved 11 December 2020 from

Cioffi, I., Evangelista, A., Ponzo, V., Ciccone, G., Soldati, L., Santarpia, L., . . . Bo, S. (2018). Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: A systematic review and meta-analysis of randomized controlled trials. Journal of Translational Medicine, 16(1), Article 371. doi:10.1186/s12967-018-1748-4

Edinburgh, R. M., Hengist, A., Smith, H. A., Travers, R. L., Betts, J. A., Thompson, D., . . . Gonzalez, J. T. (2019). Skipping breakfast before exercise creates a more negative 24-hour energy balance: A randomized controlled trial in healthy physically active young men. Journal of Nutrition, 149(8), 1326–1334. doi:10.1093/jn/nxz018

Fernando, H., Zibellini, J., Harris, R., Seimon, R., & Sainsbury, A. (2019). Effect of Ramadan fasting on weight and body composition in healthy non-athlete adults: A systematic review and meta-analysis. Nutrients, 11(2), Article 478. doi:10.3390/nu11020478

Gordon, B. (2019). What is intermittent fasting?   Retrieved 11 December 2020 from

Horne, B. D., Muhlestein, J. B., & Anderson, J. L. (2015). Health effects of intermittent fasting: Hormesis or harm? A systematic review. American Journal of Clinical Nutrition, 102(2), 464–470. doi:10.3945/ajcn.115.109553

Kerksick, C. M., Wilborn, C. D., Roberts, M. D., Smith-Ryan, A., Kleiner, S. M., Jäger, R., . . . Kreider, R. B. (2018). ISSN exercise & sports nutrition review update: Research & recommendations. Journal of the International Society of Sports Nutrition, 15(1), Article 38. doi:10.1186/s12970-018-0242-y

La Bounty, P. M., Campbell, B. I., Wilson, J., Galvan, E., Berardi, J., Kleiner, S. M., . . . Antonio, J. (2011). International Society of Sports Nutrition position stand: Meal frequency. Journal of the International Society of Sports Nutrition, 8(1), Article 4. doi:10.1186/1550-2783-8-4

Lettieri-Barbato, D., Giovannetti, E., & Aquilano, K. (2016). Effects of dietary restriction on adipose mass and biomarkers of healthy aging in human. Aging, 8(12), 3341–3355. doi:10.18632/aging.101122

Levy, E., & Chu, T. (2019). Intermittent fasting and its effects on athletic performance. Current Sports Medicine Reports, 18(7), 266–269. doi:10.1249/jsr.0000000000000614

Mirmiran, P., Bahadoran, Z., Gaeini, Z., Moslehi, N., & Azizi, F. (2019). Effects of Ramadan intermittent fasting on lipid and lipoprotein parameters: An updated meta-analysis. Nutrition, Metabolism and Cardiovascular Diseases, 29(9), 906–915. doi:10.1016/j.numecd.2019.05.056

Mundi, M. (2020). What is intermittent fasting? Does it have health benefits?   Retrieved 11 December 2020 from

Nitkin, K. (2020). Intermittent fasting: Is it for you?   Retrieved 11 December 2020 from

Papamichou, D., Panagiotakos, D. B., & Itsiopoulos, C. (2019). Dietary patterns and management of type 2 diabetes: A systematic review of randomised clinical trials. Nutrition, Metabolism and Cardiovascular Diseases, 29(6), 531–543. doi:10.1016/j.numecd.2019.02.004

Roky, R., Houti, I., Moussamih, S., Qotbi, S., & Aadil, N. (2004). Physiological and chronobiological changes during Ramadan intermittent fasting. Annals of Nutrition and Metabolism, 48(4), 296–303. doi:10.1159/000081076

Rynders, C. A., Thomas, E. A., Zaman, A., Pan, Z., Catenacci, V. A., & Melanson, E. L. (2019). Effectiveness of intermittent fasting and time-restricted feeding compared to continuous energy restriction for weight loss. Nutrients, 11(10), Article 2442. doi:10.3390/nu11102442

Seimon, R. V., Roekenes, J. A., Zibellini, J., Zhu, B., Gibson, A. A., Hills, A. P., . . . Sainsbury, A. (2015). Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Molecular and Cellular Endocrinology, 418, 153–172. doi:10.1016/j.mce.2015.09.014

Tello, M. (2018). Intermittent fasting: Surprising update.   Retrieved 11 December 2020 from

Trepanowski, J. F., Kroeger, C. M., Barnosky, A., Klempel, M. C., Bhutani, S., Hoddy, K. K., . . . Varady, K. A. (2017). Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese adults. JAMA Internal Medicine, 177(7), 930–938. doi:10.1001/jamainternmed.2017.0936

Vieira, A. F., Costa, R. R., Macedo, R. C. O., Coconcelli, L., & Kruel, L. F. M. (2016). Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: A systematic review and meta-analysis. British Journal of Nutrition, 116(7), 1153–1164. doi:10.1017/s0007114516003160