What Are the Rules of Intermittent Fasting?

Rules of Intermittent Fasting

December 30, 2021

Clinical Contributors to this story:
James Nangeroni, D.O.

Intermittent fasting is an eating style that some people use to help control their weight. You follow an eating schedule every day, only consuming food during  a set number of hours during a specific window of time, then fast for the  remaining hours.

Some people find intermittent fasting appealing because you don’t have to  remember to follow specific diet rules, scrutinizing which foods are ‘approved’  and which are not,” says bariatric surgeon, James Nangeroni, D.O. “Fasting for 12 or 16 hours each day may sound like a lot of time, but keep in mind that you’ll be asleep for 7 to 9 of those hours.

How to practice intermittent fasting  

There isn’t one single “right” way to practice intermittent fasting. Common  interpretations of this eating style include:  

  • Eating during a 12-hour window every day (between 7 a.m. and 7 p.m.,  for example) and fasting for the other 12 hours  
  • Eating during an 8-hour window every day (between 11 a.m. and 7 p.m.,  for example) and fasting for the other 16 hours  
  • Eating differently every other day: On odd days, eating sensibly  whenever you please, and on even days, restricting yourself to 500 or  600 calories for the entire day, with the bulk of calories in one meal  
  • Eating sensibly for 5 days of the week, and eating no more than 500 to  600 calories on 2 other days per week, spacing out the “fasting” days  
  • Eating sensibly for six days of the week, then fasting for the entire 24  hours on the seventh day  

People who practice intermittent fasting may adjust the eating style to fit their personal schedules. If you normally eat an early dinner and you want to fast for 16 hours a day, you can make your 8-hour eating window run from 10 a.m. to 6 p.m. If you’re a later eater, you can make your 8-hour window run from 12 p.m. to 8 p.m.  

Does intermittent fasting work? 

People may gradually lose weight when they practice intermittent fasting,  because they tend to consume fewer calories over the course of the day if they  can’t graze all day or snack late at night.  

Additionally, people may lose weight because when they eat significantly less  often, the body produces less insulin, the hormone that converts food into  energy. When you eat frequently, insulin helps your body store unused energy  as fat. But when you go without food for 12 hours or more, instead of storing  unused energy, your body burns through its existing energy stores, then begins  burning stored fat for energy, which aids weight loss.  

Adjusting to an intermittent fasting eating style  

It can be difficult to switch from an all-day eating style to a routine that  includes 16 or 24 hours of fasting, so you may want to ease into the practice. Start out by skipping breakfast for a few days to get used to fasting until noon,  or stop eating late-night snacks for a few days to shorten your eating window.  Gradually shrink the window until you’re used to eating during the desired  number of hours without feeling hunger pangs.  

It’s important to stay hydrated when you’re outside of your eating window.  Water, black coffee and unsweetened tea are all acceptable beverages that  won’t break your fast.  

Researchers are still studying the benefits of intermittent fasting, but some  studies have shown that the eating style can help people lose weight in the  short term.  

Special considerations should be made if you have ongoing health problems  and you should consult with a physician before pursuing major dietary changes.

Next Steps & Resources: 


The material provided through HealthU is intended to be used as general  information only and should not replace the advice of your physician. Always  consult your physician for individual care. 

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