Fasting to improve health or lose weight is having a moment right now. But is fasting really going to get you to your health goals? The short answer is yes, but like anything else, there’s a balance to it.
What you’ll find regarding fasting on the internet, TikTok, Instagram, and from fasting-zealot influencers can be dangerous. While it’s true that you’ll experience some good benefits with any form of fasting, there are also detriments that come along at certain extremes.
As nutrition professionals, I believe it’s our job to accurately inform and emphasize the risks just as much as the benefits. The purpose of this information is to provide you with the tools you need to make well-informed decisions that are best for you.
Fasting can take many shapes and forms. It includes everything from:
- Overnight fasting.
- Shortened eating windows (14-16 hr fasts).
- 24, 48, and 36 hr fasts.
- Religious fasting such as Ramadan, Lent, or Yon Kippur.
- Mulitple day or week water fasts.
The challenge with talking about “fasting for health” is that it encompasses so many different strategies. Information on it can be vague in light of this. How do you know if that type of fasting you’re doing is the type that offers X, Y, or Z benefits?
Just as with everything I implement with clients or share online, what matters most is how you feel doing it!
If you don’t feel well with your approach – it’s not what your body needs. If you’re thriving, that’s great! You’ve found a strategy that works great for you in this season of life. Just remember to be mindful that what works great for you may not work for others.
Where to Begin
Deciding where to start can be challenging. Let’s cover the right and wrong ways to implement a fasting regimen so that you can best decide for yourself.
Everyone should be fasting. Your body cleanses, resets, detoxes, and clears “zombie cells” when you’re fasting (1). Extended periods of not eating encourage your body to tap into stored energy, i.e., carbs and fats, and aids in weight loss and better metabolic health.
Your body needs and expects to fast each day. You can implement a healthy fasting regimen seamlessly into your life with little thought, or you can go about it in a more intentional way. The most important thing to remember is that balance is key. Problems arise if the frequency and duration are too long.
The right way to fast:
- With your circadian rhythm – stop eating 3 hours before bed and wait 1 hour after waking before eating (2).
- Time Restricted Feeding – eat only within an 8, 10, or 12-hour window (3).
- Modified/fasting-mimicking diets – caloric restriction for 1-4 days at a time (more on this below).
The wrong way to fast:
- 24-hour fasts – While this does induce health benefits, there are many downsides (4, 5).
- Extended day fasting (36, 48, 72hr) – Your body will start to break down (6). It can also harm women’s hormone balance (7, 8).
- Week-long water fasts – noticing a pattern? Too much and too often is not ideal. There might be some health benefits, but they do not come without detriments.
Will you find research, practitioners, social media accounts, and endless blogs touting that these “wrong” ways to fast are good for your health? Absolutely. And I agree – they can offer great health benefits. But what is often left out of these conversations are the downsides.
Studies have looked at the eating behavior and psychological impact of 24-hour fasting in individuals. This form of fasting can lead to irritability/mood dysregulation, increased food intake afterward, more snacking, and worsened cravings (4, 5).
You need a steady supply of amino acids from protein to support your metabolic processes. You can’t make hormones and neurotransmitters without them. They’re required for phase 2 detoxification in the liver (8). They’re also the building blocks of tissues like muscles, organs, hair, skin, nails, connective tissue, etc.
Your body starts to break down tissues after 18 hours of fasting to supply amino acids where they’re most critically needed, like hormone and neurotransmitter production (9). We want to maintain a healthy lean body mass (LBM) level. Higher levels of LBM lead to longer lifespans and health spans in humans (10, 11, 12).
Many proponents of extended-day fasting cling to studies that showed “caloric restriction increases lifespan.” What they leave out, however, is that these studies were done in yeast, worms, mice, and fish (13). The data on human lifespan and caloric restriction is inconclusive at best (13)
It’s also important to note that caloric restriction (which most human studies use) is different from fasting. While some strategies may include both, the terms are not interchangeable (13).
Humans are very different from yeast, worms, mice, and fish in several obvious ways, but one that’s most important here is that humans have a lot more weight to move against gravity – LBM is what allows us to do that and how we maintain functionality. Partaking in dietary habits that knowingly reduce LBM is not ideal for longevity.
Effects of fasting on female hormones:
While research has yet to catch up, tons of anecdotal data supports that women should not partake in extended-day fasting.
Women need adequate nutrient intake in the 3 days leading up to ovulation, as inadequate intake can inhibit it (7, 8).
I’ve worked with many women who have lost their periods after implementing these extreme diets. I’ve even seen disruptions with milder forms of fasting.
If you’re menstruating, working with a practitioner who knows how to navigate hormone balance before beginning any fasting regimen is best.
With all of these downsides that offset and even negate the benefits of fasting, why not take a more balanced approach?
Circadian Biology
Following your natural circadian rhythm is the easiest way to implement fasting into your life. Give yourself at least a 12-hour window throughout the night when you’re fasting, and eat only during the day. You can shorten your eating window to 8 hours if you choose but know that 12 hours is sufficient to reap the benefits.
This is based on legitimate research that has been done in humans. Satchin Panda of the Salk Institute has dedicated a career to studying the implications of eating with circadian biology. He outlines the immense benefits to health in his research (14).
Your body is primed and prepared to digest, absorb, and metabolize nutrients during the day. It should be cleansing, detoxing, repairing, and resetting when you’re asleep. You need nutrients in circulation from the day’s meals to perform these nightly tasks.
It’s important that you’re appropriately fueling your body in a timely manner aligned with your biology if your goal is to optimize health and well-being (15).
Intentional and Healthy Fasting Methods
Because of their restrictive nature, I’ve never been big on implementing fasting with clients except in very few exceptional cases. That all changed after seeing one client’s results with the Protein-Sparing Fasting-Mimicking Diet approach.
This form of fasting is safer, more effective, and much easier to follow than the drastic methods.
The PSFM diet protocol:
- Days 1-4: Eat 500-800kcal from protein and fat sources only. Use this guide to determine your exact protein and fat intake.
- Days 5-13: Eat a normal-caloric diet, focus on quality, whole foods.
- Repeat for for 6-8 weeks.
The beauty of this approach is that you eat enough protein to prevent tissue breakdown, but overall caloric intake is low enough that you still get the benefits of fasting without all the negatives.
Health benefits of the PSFM diet:
- Improves metabolic flexibility.
- Reduces/eliminates sugar cravings and intake.
- Improves sleep quality.
- Flushes fat out of the liver.
- Improves metabolic health.
- Improves blood sugar and insulin resistance.
- Boosts weight loss (I like to call this a “beneficial side effect”).
When Nothing Else Works
The results of this nutrition approach speak for themselves. This client’s incredible story is a testament to this. I often see women who are doing all of the “right things” but still experiencing metabolic issues. This was the case for a client who couldn’t seem to get her glucose numbers where she wanted them.
It’s common to see high fasting blood sugar in women following a low-carb diet or prolonged fasting for extended periods. The most common and effective fix is to actually increase carb intake. It usually clears things right up.
As paradoxical as it seemed, she tried it right away. It worked for a few days, then out of the blue, her blood sugars got worse.
We were exploring potential explanations for this when she sent me a podcast interview with Dr. Brian Mowll that explained a lot of what she was experiencing. He discussed how sometimes just the liver can be insulin resistant. You won’t always see it in labs, but there are other clues.
He shared that his method for flushing fat out of the liver is the PSFM diet. I asked if she wanted to give it a try, and she was eager to get started. I was synced with her CGM for the trial, and we were both blown away at what we were seeing:
- By day 4, her blood sugar levels were completely normal, with no spikes and no more high morning blood sugars.
- In 2 months, her A1c had reduced out of the prediabetic range.
- In 4 months, most of her metabolic blood markers were back within standard ranges and within optimal ranges.
- Most of her symptoms were gone, and she ceased using some meds (with the help of her doctor).
I’ve implemented this with several clients, and I can say I’ve never seen a more efficient and effective dietary intervention. But just remember, there is no such thing as a “silver bullet” when it comes to health.
There have been a few who did not respond well, which indicates the need for a more gentle approach to start. This diet is safe and healthy for the majority of people to do on their own. If you don’t respond well, this just tells you your body needs a different approach.
Blood work is a great tool for revealing what your body needs and is always a great starting point. Please reach out if I can support you in implementing this plan in a more personalized way.
