A Look at Intermittent Fasting

Clock Fasting

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Intermittent Fasting – What is it and is it for you?

Intermittent Fasting (IF) is not a new idea – fasting was recommended by ancient philosophers (e.g., Hippocrates, Socrates, and Plato[1]) and is practiced in many religions (e.g., during Lent in Christianity, Ramadan in Islam, Yom Kippur and other days in Judaism) – but it was the most-googled weight loss idea in 2020.  Intermittent Fasting has been of interest to the medical community at least since the early 1960s, when the Journal of the American Medical Association published articles regarding its potential for treating obesity.

Intermittent Fasting is an umbrella term that includes a number of different approaches to caloric restriction.  Some regimens work better for some people than others so the variety of plans offers individuals a choice – you can try them out to find one you like.  For many, IF works well, either as a way to kick-start a weight loss plan or as a lifestyle.    

What it is

Intermittent Fasting is what it sounds like – you fast for specified periods and eat when you’re not fasting.  There are two common ways to practice IF:  one is to eat few (or no) calories on certain days, the other is to restrict eating to certain hours of a day.[2]  In IF, fasting can mean consuming no calories or consuming up to 500 calories.


Here are four popular types of IF[3]:

  • 24-hour fast.  Consume no calories for an entire day.  This is usually practiced one or two days per week.
  • 2/5 or twice a week.  Fast for two non-consecutive days per week – some people ingest no calories, some consume up to 500 calories in the middle of the fast.  For the other five days, you eat as usual.
  • Alternate day fasting.  Every other day is a fasting day where caloric intake is restricted to 500 calories (some people consume no calories). 
  • Time restricted eating (TRE). This approach is measured in hours rather than days - you are not restricting calories, but can eat only within the same specific timeframe every day.  For people who can’t tolerate full day fasting, this may be an easier way to practice IF - you can eat breakfast later or cut out snacking after dinner to meet the time restrictions. In addition, this can be done two or three days a week – not necessarily every day.  Here are two examples of time restricted eating:

-   14/10.  Fast (no caloric intake) for 14 hours per day and eat only during the other 10.  For example, you could fast between 8:00 at night and 10:00 the next morning.

-   16/8. Fast (no caloric intake) for 16 hours and eat only during the other 8.  This could mean fasting between 6:00 at night and 10:00 the next morning. 

IF has been touted by many celebrities (e.g., Jennifer Aniston, Terry Crews, Chris Pratt, Gisele Bündchen[4],[5]) and some athletes (e.g., WNBA star, Sue Bird[6]), which partly explains its popularity and status as “most googled.”   Another reason is that the variety of IF regimens allows individuals to pick an option that seems least painful. 

Positive results

One of the reasons IF seems to work for weight loss is that time restricted eating – whether by day or set hours – appears to result in the intake of fewer calories per week. For example, even if you eat whatever you want within the time frame allowed, you will still likely cut out after dinner drinks and snacks, which can be a lot of extra calories.[7]  While most people try IF to lose weight, it may also offer other health benefits.

If you don’t eat for at least 12 hours (ideally 16), your body burns through glucose and starts tapping fat for fuel.  Compared to calorie-restricted diets, intermittent fasting tends to trigger more belly-fat loss.[8]

One study observed people with metabolic syndrome who received standard medical care (including statins and anti-hypertensives) who also followed a 14/10 Time Restricted Eating (TRE) pattern.  After 12 weeks, TRE led to weight loss, lower blood pressure, and lower levels of “bad cholesterol.”[9]

Intermittent Fasting may reduce inflammation and improve blood sugar levels. 

According to an Intermittent Fasting Q and A on the Mayo Clinic website,

It appears that fasting for a short time can produce ketosis — a process that occurs when the body doesn't have enough sugar for energy, so it breaks down stored fat instead, causing an increase in substances called ketones. Fasting also affects metabolic processes in the body. These processes trigger a number of responses, including decreased inflammation, improved blood sugar regulation and better response to physical stress. The research shows intermittent fasting could have other health benefits, as well, but more study is needed. [10]

Some followers of IF have reported, anecdotally, that they have more energy and clarity, and that they sleep better (which could be a result of not eating right before bed).

Possible negative side effects

Intermittent Fasting can have negative side effects, including irritability, headache, low energy, hunger, poor work or activity performance.  And some people should NOT practice IF, including the following:[11]

  • pregnant women
  • children
  • people at risk for hypoglycemia
  • people with certain chronic diseases
  • people at risk for an eating disorder

It is important to consult your physician before starting any major diet or exercise regimen.

Scallops Asparagus

Maintain a balanced diet while practicing Intermittent Fasting

Because there is little long-term research regarding IF, we don’t yet know of any related long-term health benefits or risks.[12]  We do know that if you eat only junk food, you’re not likely to lose weight.

So don’t just count your calories, make your calories count!

It’s important to maintain a healthy, balanced diet even if you restrict the time in which you’re eating.  Many of the most popular diets today (Mediterranean, keto, paleo, gluten free, whole30) include lots of vegetables, fruits, and healthy proteins, such as those found in seafood. 


Please talk with your health care provider about any complementary health approaches you use and before you make big changes in your regular diet.



[1]  https://www.npr.org/templates/story/story.php?storyId=16513299

[2]  Stiepan, D. (2020). Mayo Clinic Minute:  Is intermittent fasting a quick fix? Mar. 2, 2020. https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-minute-is-intermittent-fasting-a-quick-fix/

[3]  Martin, C. (2019). What is Intermittent Fasting and does it really work?  The New York Times, Nov. 23, 2019. https://www.nytimes.com/2019/11/23/style/self-care/intermittent-fasting-benefits.html

[4]  https://www.marieclaire.com.au/intermittent-fasting-celebrities

[5]  https://www.delish.com/food/g22617665/celebrities-intermittent-fasting/

[6]  Florsheim, L. (2021). WNBA Star Sue Bird on Intermittent Fasting and the breakfast she swears by.  WSJ Magazine, The Wall Street Journal, Jan. 4, 2021. https://www.wsj.com/articles/wnba-star-sue-bird-on-intermittent-fasting-and-the-breakfast-she-swears-by-11609767248

[7]  https://www.menshealth.com/nutrition/a29192545/intermittent-fasting-beginners-guide/

[8]  Csatari, J. (2020). 7 Intermittent Fasting benefits that aren’t weight loss.  Men’s Health, Jul. 7, 2020. https://www.menshealth.com/nutrition/a30148896/intermittent-fasting-benefits/

[9]  Wilkinson, M.J., Manoogian, E.N.C., Zadourian, A., Lo, H., Fakhouri, S., Shoghi, A., Wang, X., Fleischer, J.G., Navlakha, S., Panda, S., and Taub, P.R. (2019). Ten-Hour time restricted eating reduces weight, blood pressure, and atherogenic lipids in patients with metabolic syndrome.  Cell Metabolism, 31 (1)92-104. https://doi.org/10.1016/j.cmet.2019.11.004

[10]  Torborg, L. (2020).  Mayo Clinic Q and A:  Long-term benefits and risks of intermittent fasting aren’t yet known. Mar. 10, 2020.  https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-long-term-benefits-and-risks-of-intermittent-fasting-arent-yet-known/

[11]  https://health.clevelandclinic.org/intermittent-fasting-4-different-types-explained/

[12]  Torborg, L. (2020).  Mayo Clinic Q and A:  Long-term benefits and risks of intermittent fasting aren’t yet known. Mar. 10, 2020.  https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-long-term-benefits-and-risks-of-intermittent-fasting-arent-yet-known/

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