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Nutrition & Health Info Sheets for Consumers - Intermittent Fasting

Nutrition & Health Info Sheets contain up-to-date information about nutrition, health, and food. They are provided in two different formats for consumer and professional users. These resources are produced by Dr. Rachel Scherr and her research staff. Produced by Nora Mooney, Allison Kou, Junxi Wei, Britt Loofbourrow, PhD Candidate, Anna M. Jones, PhD, and Rachel E. Scherr, PhD.

What is Intermittent Fasting? 

Intermittent fasting is a popular eating pattern in which a person restricts the time frame in which they eat, known as fasting [1]. Some people practice it as a weight loss method. However, we need more research to prove its benefits for humans.

What are some of the different methods of intermittent fasting?

  • 16:8 Method: The 16:8 method breaks up a 24-hour day into an 8-hour period and a 16-hour period. Individuals eat food during the 8-hour period, and avoid foods and drinks that contain calories during the 16-hour period. Some eating periods may be between 10am-6pm, 11am-7pm, or 12pm-8pm, so that most of the fasting occurs during sleep [2].
  • 5:2 Method: Individuals will choose to fast two days out of the week to be fasting days. Individuals can either avoid food and drink altogether or simply eat very little (~400-600 calories per day). During the other five days of the week, individuals will eat normally [2].
  • Alternate Day Fasting: Individuals fast every other day, meaning they will eat normally on one day, fast the next day, and repeat. Fasting in this method means eating around 500 calories per fasting day [2].
  • Whole Day Fasting: Individuals choose one or two days to fast during the week. During each 24-hour fasting day, individuals will avoid foods and drinks that contain calories [3]. 

What are some reasons that people participate in intermittent fasting? 

Many people participate in intermittent fasting to lose weight. It is different from other weight loss methods because it does not focus on limiting or removing specific foods from the diet. Instead, it limits the time frame in which a person eats [1].

People may also participate in intermittent fasting for medical reasons, such as for certain medical tests, or religious reasons, such as fasting for certain holidays.

Does intermittent fasting have any health benefits?

There are mixed results about whether intermittent fasting is beneficial for human health. Some studies show health benefits from intermittent fasting [2, 4, 5] while other studies show no benefits and even negative effects [6]. Multiple animal experiments have been done to determine if intermittent fasting improves symptoms of metabolic syndrome, which include high cholesterol, blood pressure and blood glucose [7, 8]. In studies with animals, intermittent fasting lowered weight and blood pressure [7]. However, similar research is needed to learn if these effects also occur in humans.

A small human study found that intermittent fasting may have positive health effects in people with type 2 diabetes by improving pancreatic function and how insulin works in the body [8, 9, 10]. More research is needed to investigate whether intermittent fasting or the weight loss that were beneficial [11].

Intermittent fasting has the potential to reduce inflammation within the body [9, 10]. Chronic inflammation can lead to harmful conditions such as cancer [13]. It isn’t known exactly how intermittent fasting reduces inflammation, but one hypothesis is that eating fewer calories than needed could lead to health benefits over time [9]. More research is needed to learn more about possible health benefits from intermittent fasting.

Can intermittent fasting be harmful?

Even though there are benefits to intermittent fasting, there are also some risks [14]. Participants of intermittent fasting may not drink enough water or consume enough nutrients [5]. Some people might overeat after a fasting period, which may lead to weight gain over time [5, 15]. Some people who participate in intermittent fasting report having headaches and feeling depressed, tired, or easily annoyed [5, 16]. Individuals may also have a higher chance of getting infections, developing eating disorders, or becoming dehydrated [5].

References

  1. Obert J, Pearlman M, Obert L, Chapin S. Popular Weight Loss Strategies: a Review of Four Weight Loss Techniques. Curr Gastroenterol Rep. 2017;19(12):61. 
  2. Patterson RE, Laughlin GA, LaCroix AZ, Hartman SJ, Natarajan L, Senger CM, et al. Intermittent Fasting and Human Metabolic Health. J Acad Nutr Diet. 2015;115(8):1203-12. 
  3. Tinsley GM, La Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015;73(10):661-74.
  4. Wegman MP, Guo MH, Bennion DM, Shankar MN, Chrzanowski SM, Goldberg LA, et al. Practicality of intermittent fasting in humans and its effect on oxidative stress and genes related to aging and metabolism. Rejuvenation Res. 2015;18(2):162-72.
  5. Horne BD, Muhlestein JB, Anderson JL. Health effects of intermittent fasting: hormesis or harm? A systematic review. Am J Clin Nutr. 2015;102(2):464-70.
  6. Soeters MR, Lammers NM, Dubbelhuis PF, Ackermans M, Jonkers-Schuitema CF, Fliers E, et al. Intermittent fasting does not affect whole-body glucose, lipid, or protein metabolism. Am J Clin Nutr. 2009;90(5):1244-51.
  7. Longo VD, Mattson MP. Fasting: molecular mechanisms and clinical applications. Cell Metab. 2014;19(2):181-92.
  8. Barnosky AR, Hoddy KK, Unterman TG, Varady KA. Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Transl Res. 2014;164(4):302-11.
  9. Halberg N, Henriksen M, Soderhamn N, Stallknecht B, Ploug T, Schjerling P, et al. Effect of intermittent fasting and refeeding on insulin action in healthy men. J Appl Physiol (1985). 2005;99(6):2128-36.
  10. Carlson MG SW, Campbell PJ. Fuel and energy metabolism in fasting humans. American Journal of Clinical Nutrition. 1994;60:29-36.
  11. Brown JE, Mosley M, Aldred S. Intermittent fasting: a dietary intervention for prevention of diabetes and cardiovascular disease? Br J Diabetes Vasc Dis. 2013;13(2):68-72.
  12. 12.Johnson JB SW, Cutler RG, Martin B, Hyun D, Dixit VD, Pearson M, Nassar M, Maudsley S, Carlson O, John S, Laub DR, Mattson MP. Alternate Day Calorie Restriction Improves Clinical Findings and Reduces Markers of Oxidative Stress and Inflammation in Overweight Adults with Moderate Asthma. Free Radical Biology & Medicine. 2007;42(5):665-74.
  13. de Azevedo FR, Ikeoka D, Caramelli B. Effects of intermittent fasting on metabolism in men. Revista da Associação Médica Brasileira (English Edition). 2013;59(2):167-73.
  14. Aksungar FB, Topkaya AE, Akyildiz M. Interleukin-6, C-reactive protein and biochemical parameters during prolonged intermittent fasting. Ann Nutr Metab. 2007;51(1):88-95.
  15. Libby P. Inflammatory Mechanisms: The Molecular Basis of Inflammation and Disease. Nutrition Reviews. 2007;65(12):140-6.
  16. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2017;39:46-58.

Inquiries regarding this publication may be directed to cns@ucdavis.edu. The information provided in this publication is intended for general consumer understanding, and is not intended to be used for medical diagnosis or treatment, or to substitute for professional medical advice.