Dietitian Blog, MNT Guidelines, Patient Blog, Weight Management | Oct 1 2019

What’s up with intermittent fasting? Part one: The basics

Something to keep in mind before we dig into this topic is that the research is still in progress. We will cover more about this in our next intermittent fasting (IF) blog, but for now we must recognize that IF is still a relatively new topic in research (at least when it comes to applying it to all demographics of humans.)

As far as the basics go, the first thing you need to remember is that IF is not about restricting food, it’s simply about when you eat your food – it’s a pattern. I repeat, it’s a pattern of when you eat.

Today we are going to review the different types of IF (or the different patterns). It can be somewhat confusing because there are so many different names for each type of IF. But have no fear, because below you’ll find a description of each type with all the common names used. It’ll help you understand what patients or friends are talking about, regardless of what term they use.

Most common patterns of intermittent fasting

Time restricted fasting – 8:16 method or 16:8 method – 10:14 method

This pattern incorporates fasting every day. An individual will fast for a certain number of hours and eat for a certain number of hours. Most common is to fast within 16-hour time frame and eat within an 8-hour time frame. For example, you would eat between noon and 8 p.m. and fast from 8 p.m. to noon the next day.

You might also see this type called the “skip a meal” method since it’s often thought that breakfast is skipped. But remember, fasting isn’t necessarily restrictive, so it’s not about skipping meals. It’s just rearranging when you eat your meals.

Alternate day fasting – Modified fasting

With this pattern of IF, you would eat a normal diet one day (implying it’s not restrictive and includes nutrient dense food options), and then the next day you would fast. With this particular pattern, the guidelines are a little conflicting. Some say that on fasting days, you don’t consume any food while others say you are able to eat up to 25 percent of your energy needs (typically about 500 calories). Regardless of the type of fasting day you choose, you will eat every other day and fast on days in between.

5:2 method – Whole day fasting – Modified fasting

This pattern of IF looks at a seven-day week instead of day-to-day. Within a week period, you eat a normal (healthy) diet for five of those days. Then the other two days, you fast. You get to choose when you implement those two fasting days, and they do not have to be consecutive. This pattern is similar to Alternate Day Fasting in that you can eat up to 500-600 calories on fasting days.


This pattern is just a modified version of the 5:2 method, you choose one or two non-consecutive days within a week to fast. However, on the days that you fast, you completely abstain from eating altogether for 24 hours. Eat nothing, not even the 500 calories allowed on the Alternative Day Fasting method. This particular pattern of fasting is very common in many religions.

So, here’s the big take-away, IF is a pattern of when to eat. It is not about restriction or defining what to eat. Of course, it is always encouraged to follow a balanced, nutrient-rich diet while implementing IF. During Part Two of our IF series, we will look at the most up-to-date research on the risks and benefits of IF. Stay tuned!

Note to readers: The information discussed in this blog is not intended to replace medical advice. Please meet with your physician and dietitian before making any changes to your diet.

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Patterson RE, Sears DD. Metabolic effects of intermittent fasting. Annual Review of Nutrition. 2017;37:371-93.
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About Juliette Soelberg

Juliette Soelberg, MS, RD, LDN works as a clinical dietitian, and her experience ranges from long- and short-term rehab to outpatient counseling to critical care. She believes that evidence-based practice is the most effective way for dietitians to become assets to their organizations and advocates for their patients.

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