The Benefits of 24 Hour Fasting: Is it worth the hype? – Tom Coffey Fitness

Introduction To The Benefits of 24 Hour Fasting

Intermittent fasting has exploded in popularity over the last half a decade or so. The rise in popularity is, in no small part, to the many popular books that have been published on the topic. Some of these books include: Leangains, The Obesity Code, Fast Diets For Dummies, and many more.

The most common type of fasting usually involves fasting for 12 to 16 hours per day, then using the remaining 8 to 12 hours for eating. This style of intermittent fasting is referred to as 16/8 fasting.

However, there are benefits to fasting for longer than 16 hours, even as long as 24 hours.

In the rest of this article we’re going to use science to examine the 24 hour fast benefits  and help decide if a 24-hour fast is actually worth your time.

Caution: Basically until the last few paragraphs we’re going hard in the paint with science jargon here. This is mostly because I’m a closet science nerd, who has an affinity for scientific research.

However, if you want to save yourself like 9 minutes of (mostly science) reading, then here is my (non-sciency) take on intermittent fasting for 24 hours:

• Doing a long duration fast every once in a while is great from a health perspective

•If you’re experienced with fasting and interested in fasting for one full day, then I suggest you give it a try and see what you think

•If you’re not experienced with fasting yet I suggest that you cut your teeth with a shorter fast of 8-12 hours, and slowly work up to a 24 hour fast.

Ok, still with me?


Let’s do this.

Types of 24 Hour Fasts

Before we dive into the benefits of 24 hour fasting, it’s worth taking a look at two of the more popular models for this type of fasting.

Alternate Day Fasting (ADF)

Alternate-day fasting is one of the most popular styles of 24-hour fasting that is examined in the research. This type of fasting was popularized by Dr. Krista Varady in her  widely popular book titled “The Every Other Day Diet”.

Basically with ADF you eat normally on one day and then on the next day you fast for 24 hours. You repeat the cycle of one day I love eating and one day of fasting for as long as you want.

Whole-day Fasting (WDF)

Whole-day Fasting involves fasting for periods of 24 hours, but only doing so one or two times per week. You may also hear this called “The Leangains Method”.

This style of fasting seems to be growing in popularity with the general public, possibly because it’s a bit easier to implement than an full-bore ADF style fast.

Reasons To Fast For 24 hours (Science….Engage)

Intermittent fasting has been shown to increase health by decreasing metabolic risks for diseases such as diabetes, obesity, or even cardiovascular disease [1,2].

Intermittent fasting is thought to have a very positive effect on circadian rhythm, as well as on weight regulation, and even improvements in mood [4].

Weight Loss (You’re already beautiful in my book)

Intermittent fasting has been proven to successfully help people lose weight and keep it off for extended periods of time. However what’s really interesting is that multiple studies have shown that over a long enough time there isn’t a significant difference in weight loss between intermittent fasting groups in caloric restriction groups [6,8].

As it seems common problems with calorie restriction are that it tends to cause higher levels of overall hunger, which in turn leads to overeating and kicks people out of the calorie deficit [3].

It’s really interesting that  when fasting, especially for longer periods of time, feelings of hunger seem to go away. Twenty four hour fasting protocols, such as Alternate Day Fasting or Whole-day Fasting, may actually be better alternatives than long-term calorie restriction [3].

Shifting To Fat Burning Mode (Ketones. Yay)

Okay to be completely blunt fat burning mode” isn’t exactly an accurate description of what happens during longer fasts. in our bodies restore glycogen in a couple of places, namely the liver and skeletal muscle.

After about 24-48 hours of fasting we start to burn through the glycogen stored in our liver (hepatic glycogen) [12].

When this happens there is a metabolic switch from glycogen (sugar) to the production of fat derived ketone bodies and free fatty acids [7].

After liver glycogen is depleted, which really only occurs after long-term fasting (or prolonged exercise), ketone bodies, fat derived glycerol, and amino acids generate glucose to fuel the brain [7,10].

So yes, basically this means that you can use longer duration fasts (Cough **24 hours** cough) to start breaking down fat tissue into usable energy.

Ok, I feel like I need to say this because people are going to ask—NO, fasting for 24 hours does NOT mean you will enter into ketosis.

That is something entirely different and largely depends on the individual. It can actually take days to weeks to enter into ketosis.

Metabolic Function (WTFudge does that mean?)

Fasting has been shown to have very powerful health benefits on markers of metabolic function.

In a review of the fasting literature studies showed that periods of intermittent fasting lead to decreases in fasting insulin and fasting glucose levels [4]. Fasting has also been shown to cause significant decreases in total cholesterol, LDL cholesterol, and triglyceride levels [5].

Fasting has also demonstrated improvements in inflammatory markers, including C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), adiponectin, leptin, and brain-derived neurotrophic factor (BDNF) [4].

On top of the positive metabolic improvements that seem to occur with longer fasts, gut health also seems to improve. I mean this kind of makes sense, because when you’re not eating you’re giving your gut a chance to clean itself out, which seems to improve overall gut health, improve digestibility, and decrease gut inflammation.

Longer duration fasts definitely appear to have positive effects on our gut’s mircobiota [4].

Sleep (More like counting sheep)

Humans are wired to sleep when it’s dark and be active when it’s light.  only within the past a hundred years or so have humans developed the luxury of being able to eat at virtually any time of the day.

It is thought that limiting food to just the daytime may improve circadian rhythm and improve health [1].Unfortunately, most of the literature supporting the effect of meal timing on circadian rhythm is largely based on animal research.

However, we do know that in shift workers ( people who may be working at night and asleep during the day) there is an increased risk of obesity, diabetes, cardiovascular disease, and some types of cancers [1,4].

There is a growing and robust body of literature supporting the eating most of your food earlier in the day is associated with lower weight and improved health [1]. Observational studies have reported that people who ate at nighttime eat experienced poor sleep quality and a shorter overall time asleep. Nighttime eating has also been reported to increase insulin resistance which increases risk for obesity, diabetes, and cardiovascular disease [4].

As it seems more research is needed to determine if eating late at night messes up your circadian rhythm (ie…disrupts sleep), but as it seems, the answer seems to be moving in the direction of “Yes it does”.

Cancer Prevention (FU Cancer)

Although the research on this is minimal, intermittent fasting is  theorize to play a role in cancer prevention and Studies suggest that combining intermittent fasting with chemotherapy is an effective treatments of cancer [10].

The line of thinking here is that short-term fasting before and immediately after chemotherapy could be a powerful tool to help minimize adverse side effects, such as nausea. Researchers are also thinking that fasting may somehow prime chemo-resistant cancer cells to become more sensitive to the chemotherapy treatment [10].

I’m not a doctor and cannot speak on this topic any further.

However,  if using intermittent fasting as a tool to potentially help fight cancer is something that interests you, it may be worth talking to your doctor more about this.

Should You Fast For 24 Hours?

Phew, ok I know the above section was pretty heavy in scientific literature and jargon.

But the good news is that if you’re into reading the scientific research surrounding intermittent fasting I’ve provided a links to all of the studies referenced in the reference section below.

Note:  All of the studies referenced here were full studies (no abstracts) that are open source and available to the general public.

Okay, let’s have some fun and talk about if you should fast for 24 hours, or not.

First of all we do need to think of intermittent fasting as a skill.

Developing skills takes time and consistency. Fasting is no different. If you’re already fasting regularly for 12 to 16 hours per day, then yes I do think you’re ready to try a 24 hour fast.

However, if you are brand new to the idea of fasting I recommend that you start with a shorter fast and slowly work up to a 24 hour fast.

How Many Days In a Week Should You Fast For 24 Hours?

Based on my own intermittent fasting experience, hearing other people’s experience, alternate-day fasting protocol seems to be quite an enjoyable.  I mean, it is a hard sell to ask someone to eat exactly zero food every other day of the week.

Because of this, if you’re interested in fasting for 24 hours I recommend that you limit this to one day per week. This is similar to the Whole-day Fast protocol we outlined above.

Honestly, after you have some experience with fasting, intermittent fasting for 24 hours/ one time per week is actually quite easy. If fasting for 24 hours is something that interests you, which if you’re still reading this by now, my guess is it does, my suggestion is to try it once and see what you think.

As we touched on in this article there are a lot of positive health benefits that come from 24 hour fasting.

A Really Pro Tip on Fasting For 24 Hours

Ok, so you’ve taken the plunge and decided to try a full day of fasting.

Want a pro tip from someone who’s, well, done it?


I recommend eating normally one day, but end with dinner. Then, fast until the next day’s dinner.

The reason this “dinner to dinner” type of fasting works well is for a couple reasons:

• You don’t go to bed hungry which usually keeps people up

• If you’re busy the next day you’ll distract your mind from feelings of hunger

• And, when you fast this way you’re really only missing two meals (breakfast and lunch) the following day

In my experience with 24 hour fasting, the “dinner to dinner” approach seems to be a solid approach to longer term fasting. Of course, please  try whatever you think will work best for your schedule and set you up for success.

I hope you enjoyed this article.

Thank you for reading.



[2] – Intermittent fasting: the science of going without

[3] – Intermittent Fasting: The Choice for a Healthier Lifestyle

[4] – Metabolic Effects of Intermittent Fasting

[5] – Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial

[6] – Intermittent versus on‐demand use of a very low calorie diet: a randomized 2‐year clinical trial

[7] – Fasting: Molecular Mechanisms and Clinical Applications

[8] – Effect of Alternate-Day Fasting onWeight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults

[9] – Impact of intermittent fasting on health and disease processes

[10] – Stem Cells Matter in Response to Fasting

[11] – Regulation of skeletal muscle energy/nutrient-sensing pathways during metabolic adaptation to fasting in healthy humans

[12] – Prolonged fasting-induced metabolic signatures in human skeletal muscle of lean and obese men



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