What’s the hype behind intermittent fasting?


By: Sarah Pittman BS, Graduate Student in Food Science and Human Nutrition at the University of Illinois

Intermittent fasting, also known as intermittent energy restriction, is a diet strategy gaining popularity. People following this diet eat only at certain times, with the hope that restricting caloric intake will result in weight loss. There are 3 types of intermittent fasting: periodic fasting, time-restricted feeding, and alternate-day fasting.

Periodic fasting/whole day fasting:

  • Includes whole-day fasting or energy restriction
  • 1 or 2 fasting days per week and normal eating patterns the other days
  • May eat up to 500-600 calories on fasting days (25% of regular daily caloric intake)

Time-restricted feeding:

  • Eat only during a certain number of hours per day
  • Fasting for 16 hours and eating for 8 hours is an example of the 16:8 diet

Alternate-day fasting:

  • The strictest form of intermittent fasting, this pattern alternates between fasting and feast days (normal intake)
  • 2 categories:
    • Complete alternate-day fasting: no calories are consumed on fasting days
    • Modified alternate-day fasting: allows 500-600 calories on fasting days

What does the research say?

  • There is some limited research that the diet produces weight loss
  • Initial human studies that compared alternate-day fasting to eating less every day showed both works equally for weight loss
  • Most studies have been limited to just a few months at a time, so the long term benefits of intermittent fasting are unknown

Therefore, intermittent fasting has not yet proven to be a research-based, sustainable weight loss strategy. While the data does not support it as a long-term weight loss plan, time-restricted eating may be beneficial for individuals who have trouble curbing late-night snacking.


Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. American Journal of Clinical Nutrition, January 2005. Link: http://ajcn.nutrition.org/content/81/1/69.full

Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Internal Medicine, May 2017. Link: http://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2623528

Monique Tello M. Intermittent fasting: Surprising update – Harvard Health Blog. Harvard Health Blog. Published 2019. Accessed December 2, 2019. Link: https://www.health.harvard.edu/blog/intermittent-fasting-surprising-update-2018062914156

Publishing H. Any benefits to intermittent fasting diets? – Harvard Health. Harvard Health. Published 2019. Accessed December 2, 2019. Link: https://www.health.harvard.edu/diet-and-weight-loss/any-benefits-to-intermittent-fasting-diets


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