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Intermittent Fasting: Tapping Into Our Biological Roots

How did humans operate before the invention of electricity and the lightbulb? Using the sun, of course! The O.G. lightbulb, our bodies have evolved over centuries to function around the rise and fall of the sun each day, 12 hours of light and 12 hours of dark.

Centered around the timing of the sun, every cell in the human body operates on what's called circadian rhythms. You've most likely heard this term before in regards to sleep, but did you know it controls much, much more than just sleep?

Our cells expect us to operate with respect to these circadian rhythms. Eating, sleeping, digesting, exercising, breathing, thinking...all of these processes and more are influenced differently depending on the time of day.

As humans have evolved though, we have created technologies that disrupt these cycles: lightbulbs, phones, computers, televisions, etc. While these technologies are amazing in their own ways, they allow us (and sometimes encourage us) to stay up later into the night and operate for longer than 12 hours per day. Combine this with our 24/7 access to food and we can eat whenever we want, disrupting the 12-hour or less time frame our digestive systems expect from us.

Before the inventions mentioned above, humans had natural periods of feasting and fasting. They didn't have refrigerators or freezers to keep their meat from the hunt or their berries from harvest edible for long periods of time. Fasting is something our bodies expect and helps keep your digestive system (and hormones associated with digestion) functioning properly.

The term intermittent fasting is very similar to the term time-restricted eating. Both encourage the consumption of food within an 8-12 hour window, sometimes even less. Intermittent fasting may last for days depending on the length of the fast. When we consume food for more than 12 hours in a day, our bodies do not have the proper amount of time to clean and recover during sleep which prepares us for the next day.

Digestion takes a lot of energy and blood, so 13 or more hours of consuming food is very taxing for the body. When we eat, blood needs to be pumped to the digestive system in order to provide the proper nutrients and oxygen for food breakdown and absorption. That means less blood is available for other functions in the body, including cognition (brain functioning). This is why one of the benefits of intermittent fasting is improved mental ability/clear mind; the brain is able to receive more blood and oxygen. This is also why you feel lethargic after that delicious Thanksgiving dinner.

As digestion occurs, insulin levels rise in order to absorb all that new glucose that just entered the body. We are designed to have natural rises and falls of insulin throughout the day so when we are constantly eating and eating past that 12 hour window, we are producing more and more insulin. Over time, this can lead to insulin resistance and type 2 diabetes.

Intermittent fasting and time-restricted eating allow glucose and insulin levels to fall completely and put the body into a fat-burning state for a period of time. Here are some tips on how to try both for yourself and maybe implement one or both into your life.


Intermittent Fasting

  • Determine the length of your fast. It is not recommended to start with longer than 24 hours if this is new for you. Once you get more accustomed, maybe lengthen the fasts to 48 hours.

  • Make sure to get electrolytes (sodium, potassium, magnesium, calcium, etc.). You can use a sprinkle of Himalayan salt in water or an electrolyte mix with no added sugar or artificial sweetener.

  • Stick to water, zero-calorie (no artificial sweeteners) flavored water, coffee, or tea while fasting.

  • Stay away from diet soda products (you should avoid these anyways, but especially while fasting).

  • If you are sick and/or experiencing vomiting or stomach cramps while fasting you should end the fast immediately.

  • Consult a physician if taking medication to treat a pre-existing condition. Many medications need to be taken with food.

  • Please note: long-term calorie reduction is not the same as fasting. Consume maintenance calories during your eating window.

  • When you break your fast, avoid high sugar or high carbohydrate meals to keep your blood sugar from going on a roller coaster. Aim for veggies, healthy fats, and protein. Bone broth is another good post-fast option.

Time-Restricted Eating

  • Pick and eating window (12 hours max, ideally 8-10 hours) that works for your schedule each day. For example, if you go to bed at 10 pm, set the end of your eating window at 8 pm (2 hours before bed) and start your eating window somewhere between 8 am and 12 pm.

  • Your window will have to take into account the amount of food you need to eat each day. If you are attempting to lose weight, you can most likely get in your daily calories in a smaller window than someone trying to gain weight who needs more food.

  • Make sure you are finished eating by the end of your eating window. If your end time is 8 pm, that doesn't mean start dinner at 8 pm.

  • Time-restricted eating is a more consistent method to have in place for your daily life. Sticking to your window as many days as possible each week will most likely result in better sleep, improved recovery, and more energy.


Whichever method you choose to try, make it a regular practice in your life. Remember, we didn't evolve as humans having access to food 24/7 so practicing fasting or time-restricted eating is tapping into and respecting the biological roots that our bodies are designed around.

To learn more about either of these methods and see which one is right for you, feel free to schedule a free 15-minute chat with us using this link.


In wellness,

Braeden Yacobucci, RDN/RD, LD, CF-OL1

Cara Barton, OTR/L, PN1, CF-L1

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