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Intermittent Fasting - How Does it Work?

Intermittent fasting causes physiological changes and improves overall health. Learn more about how intermittent fasting works.
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Many people are trying intermittent fasting or thinking about trying it. But you might be wondering how intermittent fasting works. In this article, we discuss how intermittent fasting can cause many physiological changes that can improve your overall health.

Written by
Christine Richardson, PhD
Clinical Project Manager at Becton Dickinson

Most diets require you to watch how many calories you eat, which is burdensome, exhausting, and sometimes not effective. Intermittent fasting, on the other hand, doesn’t require you to control your calories or restrict your food, you just have to watch when you eat. 

Intermittent fasting has you decrease the timeframe you eat. And this can translate to a shorter eating window each day or going full days without eating. What’s nice about intermittent fasting is that there are a lot of variations so you can easily find something that can accommodate your lifestyle.

How Does Intermittent Fasting Work?

Whether or not you’ve tried intermittent fasting, you’ve probably wondered how it works. And that’s a great question! For years, we’ve been told that constant snacking or “grazing” is the best way to boost our metabolism and intermittent fasting is…well, the opposite of that, so it’s natural to wonder how this diet works. 

There are a few theories to explain how intermittent fasting is so effective and we will discuss them here.

Flipping the Metabolic Switch

Light switch.

When you don’t eat for a prolonged period of time, your body starts to run out of its stored sugar and will switch to using more of your stored fat for energy to fuel normal bodily processes. Some scientists have called this “flipping the metabolic switch” and people who use more fat for energy are called “metabolically flexible” (1).

What this means is that you literally teach your body how to burn more of your stored fat. This is how you can obviously lose body fat, and this is also what helps you become a healthier version of yourself.

Studies have shown that people who are more metabolically flexible are at less risk for developing metabolic conditions, especially insulin resistance (the underlying cause of diabetes type 2) (2).

This is all probably because we didn’t evolve eating all day every day. Our ancestors would go many hours each day or even days at a time without eating. With today’s modern agriculture, food is more readily available, which is great, but it also means that we are consuming food more frequently than what we have adapted to over time.

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Weight Loss

A scale and a measuring tape.

Intermittent fasting is an effective tool for weight loss. Yes, you are likely losing weight because you’re flipping your metabolic switch, and yes, becoming more metabolically flexible is associated with a decrease in your risk of diseases…but we can’t ignore how weight loss is contributing to improvements in your overall health.

Studies have shown that being overweight or obese increases your risk of developing various metabolic conditions such as type 2 diabetes, cardiovascular disease, cancer, non-alcoholic fatty liver disease, and more (3)

The weight loss you experience through intermittent fasting can contribute to improvements in your overall health. 

Circadian Rhythm

Moon behind trees at night.

Most of our bodily processes adhere to a certain rhythm based on the pattern of the sun i.e. sunlight and darkness. For example, digestive processes are upregulated during the day and continuously subside as the day goes on.

We evolved this way to maximize our chances of survival. Our bodies try to conserve energy by decreasing certain processes during times our ancestors were less likely to use them – we don’t eat while we sleep, so we don’t need those processes. Make sense?

This all being said, this is why restricting your eating window each day, like in a 16/8 diet, and not eating too late at night is incredibly beneficial for your health. Studies have shown that disruptions to your circadian rhythm are associated with an increase in risk for certain metabolic disorders such as insulin resistance, hypertriglyceridemia, hypertension, and more (4,5). 

What this all means is that intermittent fasting can help make sure you are eating in a window that aligns with your bodily processes, thereby allowing for improvements in your health.

One thing to keep in mind, however, is that you can still do intermittent fasting and disrupt your circadian rhythm. If you try alternate day fasting and are still eating midnight snacks, you are eating at a time when your body isn’t necessarily ready for food. Regardless of what fasting diet you choose to do, try not consuming calories past a certain time in the evening like 7:30pm or 8pm. Make the timing realistic to your personal schedule and commit.

Bottom Line

In summary, intermittent fasting helps you become more metabolically flexible, lose weight, and can align your daily eating pattern with your circadian rhythm. Put all of these together and you have a recipe for a diet that can really help decrease your risk of metabolic diseases. 

If you want to learn more about intermittent fasting or are looking for a group to help you with your fasting journey, join our community of women who are interested in intermittent fasting!


1. Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG, Leeuwenburgh C, Mattson MP. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity. Blackwell Publishing Inc.; 2018. p. 254–68. 

2. Goodpaster BH, Sparks LM. Metabolic Flexibility in Health and Disease. Cell Metabolism. Cell Press; 2017. p. 1027–36. 

3. Pi-Sunyer X. The medical risks of obesity. Postgrad Med [Internet]. NIH Public Access; 2009 [cited 2021 Jul 1];121:21–33. Available from: /pmc/articles/PMC2879283/

4. Mattson MP, Allison DB, Fontana L, Harvie M, Longo VD, Malaisse WJ, Mosley M, Notterpek L, Ravussin E, Scheer FAJL, et al. Meal frequency and timing in health and disease. Proc Natl Acad Sci U S A [Internet]. National Academy of Sciences; 2014 [cited 2021 May 6];111:16647–53. Available from: /pmc/articles/PMC4250148/

5. Huang W, Ramsey KM, Marcheva B, Bass J. Circadian rhythms, sleep, and metabolism. Journal of Clinical Investigation. 2011. p. 2133–41. 

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