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Intermittent Fasting

Written by: Samantha Migliore
Friday April 26, 2019

Chances are you've heard about a dieting style that has gained popularity over the past couple of years, intermittent fasting. But what is it exactly? Intermittent fasting is a diet style that cycles between periods of fasting and periods of unrestricted eating. There are different types of intermittent fasting, which vary by the restriction period length and the amount of food eaten during the restriction period. The various types of intermittent fasting are:


  • Complete alternate-day fasting: involves alternating between complete fasting (all energy-containing food and beverage) and unrestricted eating over a period of two days

  • Modified fasting: allows for 20-25% energy consumption on fasting days. People using this regimen typically follow a 5:2 cycle (2 days restriction, 5 days unrestricted)

  • Time- restricted feeding: involves time windows throughout each day of restriction and no restriction (i.e. only eat between 12pm - 8pm).

Intermittent fasting is promoted as a diet that will result in weight loss, metabolic health, and help to improve high blood pressure or high cholesterol levels. But how much of this is true? A systematic review published in the Journal of the Academy of Nutrition and Dietetics looked at 13 different human intervention studies involving the three categories of intermittent fasting. It was concluded that any intermittent fasting regimens could result in weight loss, but there was little evidence that this method was any more effective than basic calorie restriction. There is little to no evidence supporting claims that intermittent fasting can help other conditions or diseases, such as high blood pressure, diabetes, or CVD. Although there are limited studies, the review also concluded that time-restricted fasting with a nighttime fasting interval has potential to help lower fasting glucose and improve HDL/LDL levels due to synchronization with daily circadian rhythm.

Although intermittent fasting has been shown to result in weight loss, it is not for everyone. Fasting periods of any length (16-24 hours) could be difficult for a person who is accustomed to eating every few hours. It may be an unsustainable lifestyle change and basic calorie restriction could be a better option. Intermittent fasting is not appropriate for people with diabetes (or other conditions that require food due to medication), actively growing adolescents, people with eating disorders, or pregnant/breastfeeding women. Another study published in the Academy of Nutrition and Dietetics, by Janet Polivy, looked at the psychological consequences of food restriction. She found that voluntary food restriction could result in “excessive eating or bingeing when restrictions are lifted, heightened emotional responsiveness, and cognitive disruptions,” (Polivy, 1996). The intervals of unrestricted eating which follow the periods of restriction could result in a calorie surplus, which could ultimately offset the deficit from intervals of fasting.

All in all, intermittent fasting has the potential to result in weight loss, but there is not enough evidence to say it is any more effective than fundamental calorie restriction. If utilized, the fasting interval regimen should be chosen to best fit lifestyle and habits. Intervals of fasting and food restriction have the potential to have psychological consequences, which could counteract any progress made during periods of restriction. Therefore, intermittent fasting is not a one size fits all diet and would work better for people who are accustomed to eating only 1-2 meals/day or do not eat for long periods of time.

References:
Diet Review: Intermittent Fasting for Weight Loss. (2018, January 19). Retrieved April 19, 2019, from https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/intermittent-fasting/

Patterson, R. E., Laughlin, G. A., LaCroix, A. Z., Hartman, S. J., Natarajan, L., Senger, C. M., . . . Gallo, L. C. (2015). Intermittent Fasting and Human Metabolic Health. Journal of the Adademy of Nutrition and Dietetics, 115(8), 1203-1212. doi:https://doi.org/10.1016/j.jand.2015.02.018

Polivy, J. (1996). Psychological Consequences of Food Restriction. Journal of the Academy of Nutrition and Dietetics,96(6), 589-592. doi:https://doi.org/10.1016/S0002-8223(96)00161-7