5 Reasons We All Should Fast, and 1 Reason Why We Shouldn’t

fasting, intermittent fasting, longevity, weight loss, health

I wanted to write this article to address a question I hear often:

Do I need to Fast to Be Healthy?


In short, probably. But what exactly does that mean?


Thanks in large part to Dr. Jason Fung and others, intermittent fasting (IF) has emerged from the shadows of the health movement to now being discussed every day on social media, as if we have been doing it for decades.


And here’s the secret: We actually have been doing it for decades. In reality, it’s more like centuries.


Think of how we evolved. There wasn’t a convenience store, grocery store, restaurant, or fast food joint on every corner.  We had to hunt and forage for our food. That took time and was sometimes unsuccessful. The natural result, therefore was periods of eating interspersed with periods of fasting.


Modern society is a far cry from that evolutionary period, as we now have a 24/7 eating cycle with late night taco runs, vending machines and snacks available at a moment’s notice, and misguided advice that we need to eat every two hours to stimulate our metabolism and lose weight (awful advice with no scientific backing, mostly promoted by snack food companies).  We have plenty of reason to believe this constant eating cycle has contributed to our current obesity/diabetes/insulin resistance epidemic.


The good news is that we can reverse that trend. We can reverse it by bringing back fasts.


What exactly is fasting?


First we need to define what fasting means, and what time restricted eating means. Time Restricted Eating (TRE), means eating only in a specific time window, and not eating the rest of the day. For instance 18:6 means not eating for 18 hours straight, then eating over a 6-hour period. This can be 12:12, 16:8, 18:6 or even 22:2. They key is that you have an extended period of time each day when you are not consuming calories.


More extensive fasts, 24-72 hours or even longer, are really what we refer to when we say intermittent fasting. For this explanation, I will refer to extended fasts and TRE together as they have similar benefits. I will explore the differences and go into more scientific detail in a future post.


Here are the top 5 reasons we should all fast


1.    Fasting is the most efficient way to lose weight.

Forget the fat burning foods, forget the cleanses and detoxes. Not eating is the key to losing weight. But do it intermittently. That’s why it’s called intermittent fasting. Chronic calorie restriction doesn’t work long term since it forces our bodies to reduce our resting metabolic rate (RMR), thus stalling weight loss and increasing frustration. Intermittent calorie restriction, on the other hand, allows for weight loss without changing our RMR, the key to healthy and successful long-term weight loss.


2.    IF is a great way to lower insulin.

It just makes sense. If there is no food coming in, there is no need for insulin to rise. Insulin will stay at its low steady basal rate, and there will be no elevations or spikes. That keeps the area under the curve low, right where we want it. Low insulin means we can mobilize our fat stores, and possibly more importantly, it protects us from the harmful long-term effects of hyperinsulinemia.


3.    Intermittent Fasting is the key to longevity.

The one consistent finding in longevity research, from single cell organisms up to primates, is that calorie restriction works. But as we have learned from chronic calorie restriction experiments in humans, it’s not so clear cut. First, its miserable and most people would rather die younger that live longer with chronic calorie restriction. Agree?

Second, our bodies adapt to chronic calorie restriction and thus make it difficult to maintain the health benefits. Intermittent calorie restriction, on the other hand, has the promise of all the longevity benefits without all the baggage that comes with it. The fountain of youth only helps if we like how it tastes.


4.    It’s easy!

What’s easier than skipping breakfast? No planning, no shopping, no cooking, no cleaning. Simply walk out the door.  In our hectic everyday lives, we should welcome anything that takes less time and makes our lives a little easier. Fasting does exactly that. Just make sure you bring a water bottle with you wherever you go, and maybe some sea salt to put in your water. Stay well hydrated and enjoy the simplicity.


5.    There are many ways to make fasting work for you.

 There is more than one way to have a successful fast. As mentioned previously, 18:6 can work wonders for most people. For those who are more adventurous, a 72-hour water fast can have amazing results. And there is everything in between. Just follow the simple rules of staying hydrated, paying attention to how you feel, avoiding anything with calories, and even avoiding calorie-free sweeteners. The rest of the details can be individualized to fit your life and your goals.


The Top Reason Why You shouldn’t fast


Fasting can work wonders for most people, but it can also be dangerous for others. If you take medications for diabetes, hypertension or other medical conditions and you’re trying to fast on your own, don’t do it! Fasting can cause significant harm in these circumstances if not done with proper precaution. That doesn’t mean it can’t be done. In fact, it can still be incredibly beneficial. Just make sure you are working with an experienced clinician who can help coach you through it safely.


Here’s one last bonus tip.


Don’t give in to temptation once the fast is over.


How you break your fast can be just as important as how you fast.


  1. Break the fast with a small low carb snack such as bone broth
  2. Have your first meal an hour or two after your snack
  3. Resist the urge to “reward” yourself with high carb foods or junk food. Your gastrointestinal system isn’t ready for that. Plus, why work so hard to keep insulin low if you are just going to spike it when you are done? Stick to your usual, healthy, high quality low-carb fare.
  4. Resist the urge to increase your calorie intake to “make up” for the fast. If anything, the first 12 hours should have fewer calories than your usual eating pattern, slowly returning to normal (not supra-normal) over the next 24 hours.


Pretty easy, right? I am a big fan of simple, safe and effective. When done right, intermittent fasting hits all three criteria.


Is intermittent fasting right for you? It may just be.

If you are interested in Fasting, but are unsure where to start, or want to learn more of the benefits, my free Full Guide to Fasting E-Book is for you!



This E-Book discusses the benefits of fasting, an overview of different types of fasting, and a guide on how to fast correctly, so that you can see the best results.

Thanks for reading,

Bret Scher, MD FACC

Founder, Boundless Health





8 thoughts on “5 Reasons We All Should Fast, and 1 Reason Why We Shouldn’t”

    1. Thanks Glen! Great to hear from you. I saw a nice write up about you in the local paper. Nice work! I am sure your book is getting lots of well deserved attention. 

    1. I’m glad you enjoy it. For me, that is the secret to health and longevity- finding things that are effective and people actually enjoy doing!

  1. Thanks for the short blog on TRF/fasting. Aside from the immediate benefit of weight loss (for me at any rate) it seems as though, as I understand it, one of the positive side effects is keeping your basal insulin at a relatively low level except during the periods that you actually need it. For those of us who are both overweight and elderly (71) additional questions have to do about advisability of fasting for longer than… say 24 hours… and the relative importance of protein/muscle loss particularly in the more elderly population. I’m assuming that if one meets the criteria or most of the criteria for metabolic syndrome that one is insulin resistant and even if the A1c is in the normal range it is likely that the insulin levels are probably at the “diabetes in situ” level.


    In any event I have not really seen any information that provides a consensus between Phinney and Fung regarding protein/muscle loss during fasting and I suspect that would be a more critical issue amongst the elderly to resolve… particularly since insulin resistance is correlated with age as are difficulties metabolizing protein/losing muscle. (On a slightly different topic there doesn’t seem to be explicit guidance in the keto world on protein intake for the elderly on a low-carb diet… Can you be on a keto diet with high protein if not a carnivore… What would the recommended levels be… as much as you like until you stop losing weight? … or what other criteria might be involved?) I may have just missed this information as I cruise the Internet… and I do understand that any given answer would have to be in the context of the individual and their particular situation.

    1. Hi Joe. Great questions. Maintning muscle mass is crucial at any age, but especially as we get into our 70s and beyond. Morbidity and mortality from falls is essentially nonexistant until we get into our 70s and older, and that can theroretically be completely preventable with proper strength maintenance. Most of the studies showing muscle loss with fasting are longer than 5 day fasts. That doesnt mean it cant happen on shorter ones, but it is less common. Personally I feel one key is to maintain resistance training during a  fast to continue to stimulate muscle growth/maintenance, and to make sure that continnues while refeeding. That is also why I recommend starting a fasting protocol under professional guidnace to ensure it is being done safely. As for protein intake on a keto diet, much of that can depend on your baseline insulin sensitivity and your activity level. You can easily measure your ketone levels and see how they change with varying amounts of protein intake. Then you can decide how to best strike the balance between muscle mass maintenance and treating insulin resitance. It is a balancing act that is different for everyone but is also completely doable with the right information. Thanks for your comments! 

  2. Hey. I’m currently a senior in high school. I am 6’2 and I still have a couple more inches to grow. I weigh 280 pounds and carry most of it in my stomach but I do have dense bones and muscle. Would a time restricted fast negatively affect my growth or overall health? Also I would choose a time restricted one and not a intermediate fast because that is too extreme for me. I hope you can help me out!

    1. Hi Peter. Thanks for your message. While I can’t give any specific advice for you as an individual, I can say that under proper guidance, time restricted eating timed appropriately with exercise can show benefits for body composition. They key would be working with someone to find the right timing for you.

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Bret Scher, MD FACC

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