Whether you are new to intermittent fasting or have been doing it for a while, you might have never considered doing a 24-hour fast. We get it, not eating for 24 hours…an entire day!…seems pretty daunting at first. 

You could practice intermittent fasting your entire life and not ever complete a 24-hour fast, and that’s ok.  But if you have been fasting for at least 18 hours and you want to give a longer fast a try, what better opportunity than Thanksgiving? A 24-hour fast means you’ll have to skip breakfast and lunch on Thanksgiving day to then feast on your holiday favorites, likely with more gusto and appreciation than if you had been munching all day. Use the LIFE Fasting Tracker to stay motivated!

Benefits of a 24-hour fast

One of the biggest benefits of performing a 24-hour fast is that your body will be in a state of heavy ketosis for a longer period of time than it might be otherwise.  Ketosis is the process through which your body uses stored fat as its primary energy source once it’s exhausted the glucose (sugar) from your last meal and the glycogen stored in your liver.

Another benefit of a 24-hour fast is that your body has the chance to perform autophagy, the process through which your body removes old and damaged components, or turns them into things your cells can use. Recycling is good for your body too!

While we still have a lot to learn about autophagy, it’s being increasingly linked to having an improved healthspan: having a body that performs and behaves younger than the actual years you’ve lived.

Fast with us for the 24 hours leading up to Thanksgiving lunch or dinner! Use the LIFE Fasting Tracker to stay motivated.

Stages of a 24-hour fast 

When you finish dinner, your body starts breaking down the food for energy. It uses some of the energy to fill your liver with glycogen, which is just a string of glucose (sugar) molecules. Any excess calories are converted to triglycerides and stored in fat cells.

First 8 hours: Your body is running off of the food from your dinner. The fat, carbohydrate and protein from that meal are broken down and used to meet your body’s energy requirements. 

Hours 8-12: For the next 4 hours, your body has typically used up all of the energy from your last meal and it’s turning to a wonderful source of stored energy: glycogen from your liver!  Your liver typically has several hours worth of energy stored at any time.

Hour 12: Once you’ve hit 12 hours into your fast, the energy from your food is long gone, and the energy stored in your liver is starting to run out as well.  At this point your body will begin turning to the largest energy store you have access to – your fat!  Fat is incredibly energy-dense, but your body can’t use it as-is for fuel, it needs to convert that fat into ketone bodies for energy.

When the ketones in your blood or breath start getting elevated, you know your body has turned to fat as its primary fuel source.  Having ketone bodies in the blood or in your breath is where the term “ketosis” comes from.

The best way to know when you’ve reached ketosis is to test your blood or breath using a ketone meter.  We have our favorites (BIOSENSE and Keto-Mojo) available for purchase at a discounted rate in the app.

Hour 18: Once you are at the 18-hour mark, your body has typically switched over entirely to ketones from fat as its energy source. At this stage most people are in “heavy” ketosis.

24 hours: By the time you hit 24 hours, autophagy has also typically ramped up and your body is recycling underperforming and damaged cells.  Congrats, you’ve made it!

What to eat before a 24-hour fast

Eating low-carb  is a good idea before any fast. Eating a meal rich in healthy fats, such as lean proteins, avocados, nuts and plant-oils will keep you full longer. Eating a lot of simple and refined carbs, such as white rice, bread, pasta, sweets, and juices, will shoot your blood sugar and insulin sky-high, making you feel sluggish and hungry soon after. When eating carbs before a fast, go for the complex kind. These include whole fruits and grains, vegetables, brown rice, and legumes. Complex carbs have fiber which slows the absorption of glucose as well as the rise of blood sugar and insulin. Having less available sugar in your system will help you enter ketosis (fat-burning mode) faster, as there won’t be as much readily-available glucose floating around from your last meal. It will also help you get better sleep

Tasty and healthy salmon steak with asparagus, broccoli and red pepper on a gray plate. Top view. Flat lay.
Eat a low carb meal before any fast to stay full longer.

Getting through a 24-hour fast

The hardest part of fasting for 24 hours is getting hungry!  

A 24-hour fast typically involves skipping breakfast and lunch, so there will be times when it feels like the hunger is just too much to take. If you ever feel negative side effects or feel unsafe at all throughout your fast, have some food, talk to your doctor if necessary, and try again another day.

When you fast for 24 hours you are going to have to battle ghrelin.  Ghrelin is a hormone released when your stomach is empty and has the effect of telling your brain you are hungry, and also prepping your body for energy storage. Just remember that the effects of ghrelin (hunger) only last a little while and then typically subside.  It can be helpful to keep yourself busy (make a phone call, go out for a walk, decorate your Thanksgiving table, etc) or have some calorie-free fluids (such as hot or cold coffee or tea) to help you get through the hunger pangs.

Something that can also be helpful when struggling with feeling hungry is to think about all the benefits happening in your body during this time.  We talked earlier about autophagy, but research is also revealing good things that happen in your brain while in a fasted state.

There is a chemical in your body called Brain Derived Neurotrophic Factor, or BDNF for short.  This chemical plays a role in learning, memory, and overall keeping your brain flexible and healthy.  

As you age, BDNF gradually declines.  Recent research has demonstrated that the levels of BDNF in your body increase with fasting.  It can be powerfully motivating to think of how you are taking care of your brain and helping prevent age-related decline in brain health as you fast!

How to break a 24-hour fast 

In the case of Thanksgiving, with a feast…but start small!

Homemade Roasted Thanksgiving Day Turkey with all the Sides
Enjoy your Thanksgiving feast after your fast!

 Fill your plate with some protein (like turkey breast), vegetables, legumes and whole grains – green beans, carrots, collard greens, sweet potatoes, beans, etc, and save the carb-loaded Thanksgiving dishes for last. Before you dig into your plate, take a moment to breathe and take in all the smells and colors of your plate. Take a fork-full of each dish at a time, savoring each bite. As you eat, take some pauses to chat with the person next to you, comment on how wonderful the food is, take some swigs of water or wine. After you’ve tasted everything, decide what you want to eat more of based on how you feel and what tasted best to you. This mindful eating approach to Thanksgiving will not only help you enjoy the meal more and notice all the tastes and flavors, but will help you tune into your satiety level and stop eating before you reach that point of being completely uncomfortable or “stuffed.” Plus, you want to leave room for dessert!

When it’s not Thanksgiving, similar rules apply. Start small to avoid overeating and limit or avoid simple carbohydrates such as sugar, white breads or pastas, sweets, etc.  Your meal should have a nice balance of protein, complex carbohydrates, and healthy fats.  A simple way to think of it is to have a protein with some veggies, along with some nuts, seeds, or healthy oils.

If you are cooking

Preparing meals while fasting will make it harder to stick to your fasting goal, but it can be done! Keep water around at all times and try getting someone else to taste the food for you. 

Doing a 24-hour fast isn’t for everyone, but hopefully you’ve learned there are some considerable benefits to giving it a try.  It can be done healthily and safely, and you might just find that it becomes something you enjoy.  

Happy fasting!



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