Intermittent Fasting: The Basics
- Stacey Schley, MD
- Aug 23, 2020
- 3 min read

I’m sure you’ve heard of it – It’s shiny. It’s new. And it’s the latest craze now that keto has died down a bit. Intermittent fasting. Your co-worker is doing it. Your mother-in-law is doing it. Celebrities are doing it. So why aren’t you?
Before you jump into this latest craze, let’s all step back, take a few deep breaths, and learn what in the world we are talking about. In reality, very few individuals are following intermittent fasting in its purest form. Instead, intermittent fasting has become a very non-specific term relating to a myriad of diets during which an individual takes a break from eating or reduces calories for some specific duration of time. If we are being honest with ourselves, we’ve all been doing this our entire lives. Breakfast, after all, is breaking the overnight fast.
The new and improved form of this ideology, however, takes on a number of different shapes:
1) Timed-restricted feeding: this is one of the most popular forms of intermittent fasting at present. Basically, this involves extending some period of normal fasting (such as the period overnight or between meals). Traditionally, this involved eating over an 8-hour span (say 9AM-5PM) and fasting for 16 hours overnight (16/8 diet). However, as you might imagine, this concept can have numerous modifications simply by changing the fasting-to-eating ratio.
2) 5:2 diet: Another popular form of intermittent fasting. This is more accurately qualified as a type of modified fasting. On this diet, individuals never 100% restrict their feeding. Instead, on 2 days out of the week, they aim to eat ~25% of their normal allotted calories and on the other 5 days of the week they eat normally. There is no true fast on this diet, rather just a restriction of kcals for a specific amount of time.
3) Complete alternate-day fasting: If you are a purest, this one if for you. As the name implies, you completely fast every other day on this diet.
4) Prolonged periodic fasting: Simply put, this is a less frequent though more prolonged period of fasting. For example, some individuals choose to fast for an entire week on a quarterly basis throughout the year.
5) We could keep going here . . . for example, I went on a date about a month ago, and the guy fasted every day at lunch. When I asked why, he didn’t have a great reason. He just felt like this was “healthy” for him. Maybe it worked for him, though I’ll never know--- we didn’t make it past date #2.
You may think that the above terminology is all just semantics, but as we dig into the research, you will see that isn’t necessarily true. True periods of fasting may, or may not, have benefits above and beyond time restricted feeding due to “flipping the switch,” which I’ll talk more about in the near future. Before we get started, you should know that I left this research with more questions than answers, but that’s the fun of it. Diet and exercise are constantly evolving fields. Breakfast was once the most important meal of the day. Today, intermittent fasting is challenging that thought. Tomorrow, I might tell you that there is a study to suggest that you should eat two breakfasts every single day. Wouldn’t we all like to jump on that bandwagon?
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