Is Intermittent Fasting Healthy?

By: Chris Freytag, CPT // December 22, 2019

As a fitness expert for decades, it’s no surprise we aren’t into fad diets or crazy concoctions that claim they’ll help you lose weight. I recommend the 80/20 philosophy—aim to eat right and make good choices about 80% of the time, but leave 20% room for indulgences and your favorite treats. So when we heard that people have been trying intermittent fasting as a way to lose weight, we were curious. Does this actually work? Is it safe? We researched whether or not intermittent fasting is healthy so we can tell you our honest opinion.


Enter your email & get this article sent to your inbox.

    We won't send you spam. Unsubscribe at any time.

    What Is Intermittent Fasting?

    The concept of fasting is nothing new—people have been fasting for religious reasons for centuries. Fasting itself simply means to go a stretch of time without eating. We all naturally fast when we sleep every night. Intermittent fasting does not require you to go more than 24 hours without eating. Instead, you have a few options:

    • Fasting Window. You can choose a fasting window of which to not eat during the day, typically around 16 hours. Because you spend roughly 8 hours per night asleep (naturally fasting,) you’re then only required to tack on an additional 8 hours of fasting during the day. Many people choose to fast 4 hours before they go to bed, and 4 hours after they wake up—skipping breakfast. You can still drink water, coffee, and tea during your fasting hours.
    • Full 24-Hour Fast. You can do a full 24 hour fast once or twice a week, so from 7 pm Friday to 7pm Saturday, for example. You can once again still drink water, tea, or coffee during your fasting period. You return to normal eating after the fast is over, meaning you aim to consume the same amount of calories you normally would, not more, after you’re done fasting.

    Related: The Science of Skipping Breakfast

    Why Do People Do Intermittent Fasting?

    From our research, we read many accounts of people who have tried intermittent fasting for different reasons, both relating to physical and mental well-being. But here are the three biggest reasons for intermittent fasting that we’ve come across.

    Should you try intermittent fasting?

    1) A Belief That It Burns More Fat

    Some people believe that by fasting intermittently, you are able to reset your digestion, helping your body burn fat more effectively and ultimately lose weight. It takes about 6-8 hours to digest a meal. Some people think that by fasting for that amount of time, you then force your body to use stored fat—and not your food—as energy. The belief is that this burns up the fat instead of the food.

    2) To Create a Calorie Deficit

    By eliminating one meal out of your day, it’s suggested that you’ll create a calorie deficit. While it’s true that you need a calorie deficit (fewer calories going in than the amount of calories burned) in order to lose weight, if you are too hungry from fasting you can overeat at your next meals and end up eating just as many calories—if not more—than you would if you ate throughout the day.

    3) A Desire To Retrain Your Appetite

    Proponents of intermittent fasting will tell you that by doing this, you train your brain to only eat when you’re truly hungry, not by arbitrary times of the day (breakfast, lunch, and dinner). Some people claim that this can help people who tend to over-eat or binge-eat better identify when they are actually hungry. However, as noted above and as we’ll discuss in further detail below, fasting can actually cause “rebound overeating” in some cases.

    Negative Side Effects of Intermittent Fasting 

    • Rebound Overeating

      This is perhaps one of the biggest drawbacks to intermittent fasting: it makes you overly hungry so you end up overeating and consuming more calories than you normally would at your next meal.

    • Mood swings

      Some people are particularly sensitive to drops in blood sugar. (Have you ever heard the term “hangry?”) Intermittent fasting can cause anxiety, irritability, and mood swings.

    • Poor sleep

      Going to bed when your stomach’s growling is never a good idea. Being hungry can wake you up in the middle of the night and keep you from getting a solid night’s sleep.

    • Weakness or fatigue

      It can be harder to work out when you feel hungry or unsatiated, and you can experience muscle weakness, headaches, or just overall fatigue.

    • Adrenal stress

      You can place undue stress on your adrenals by making your blood sugar spike and drop so significantly.

    • Lack of nutritional guidance

      Fasting doesn’t require that you eat certain foods during the time you’re actually eating. Because of this, you can technically eat whatever you please when you’re not fasting…and that lack of direction won’t help someone lose weight who consumes unhealthy foods for the rest of their day.

    What We Think About Intermittent Fasting

    There is no one-size fits all approach to nutrition. Our bodies have different needs. Some of us are sensitive to dairy or gluten, while others may be deficient in things like iron or magnesium. Some people are comfortable going long stretches without eating, while others feel the effects of low blood sugar a few hours after a meal. Finding the nutritional strategy that works for you is all about identifying what makes your body feel good and operate most efficiently.

    As a trainer and health coach, however, the concept of fasting does not make me think “fat loss.” What proponents of intermittent fasting might not realize is that fasting doesn’t cause your body to break down only fat. When you don’t consume carbohydrates after about six hours, your body will begin to convert some lean tissue (meaning muscle) into carbohydrate as well. Your metabolism needs fuel in order to work efficiently. When you starve your body, your metabolism shuts down to conserve energy. In some fasting cases, you’ll burn less fat than if you actually fueled your body with healthy food regularly, because glucose must be present for body fat to burn.

    Here’s what I suggest for people to stay healthy and burn fat:

    This is what we want for both fat burn and long-term health: a metabolism that runs efficiently—not one that’s constantly going into starvation mode. Have you tried intermittent fasting? What works best for you? Let us know in the comments below!

    Dietary Trends, Food, Nutrition

    Printed from


    on Reply

    I have been intermittent fasting for over three years, and have lost 25 pounds and kept it off. It is not a “fad” as suggested, but a lifestyle change. I have never felt better, and I am truly not hungry (and certainly not “starving”) after my 16 hour fast. I eat nutrient dense foods and am more mindful of what I eat. I also work out on the morning, and do not like exercising after eating, so this lifestyle works well for me. At my annual checkup this past month, my doctor was very impressed with my numbers, and suggested that I continue what I’ve been doing for 3+ years.

    on Reply

    Works for me, I have been doing it for 6 months. That, coupled with serious workouts have helped me shed 23 lbs. I will be 65 next month and have not been this thin for 40 years. I feel great. It is not for everyone, there is not a one size fits all in dieting.

    on Reply

    I started fasting every Monday several years ago. I initially started because of the studies on cells and brain changes, but I was going to work up to twice a week, which I never did. We eat out a lot on weekends and I found that my body really liked the chance to reset on Monday’s and if I skipped fasting, I would feel it all week. I never lost any weight from it, but that was never my reason to fast, so my diet never adjusted for weight loss. However, now that we have been home for weeks and not eating out as much, having healthier and better times meals, I have given up my weekly fast and feel just fine. I just want to add, I had just found and been working my way through the Gold videos when this all started, and am so glad because I have loved the quarantine videos.

    on Reply

    My doctor recommended it as a way to help kick start weight loss but also to help the body with blood sugar, when I had my annual physical my blood sugar was elevated but not terrible and I've struggled for the most part of the last 10 years with added weight, with hyperthyroid and being over 55 with the struggles of menopause the doctor wanted me to try it. Reluctantly I did after a lot of research, I ensure I get mostly veggies, fruits, nuts and lean proteins and I still exercise. I was concerned that I would feel even more tired than I do on a daily basis but I found that I actually have more energy and have lost a few pounds, I am careful to ensure I get within my calories for the day but I also pay attention to my macros and I exercise daily. While my weight loss hasn't been crazy big my body is finally giving it up a little at a time which is what I wanted. I'm not a fan of making myself wait till 11 to eat as I wake up most morning (4am) hungry but the results have been good and because I am 60 lbs over weight this is working. I think its important for people to do their research and work side by side with their doctor on any plan to lose weight, even though I have a degree in nutrition (like 35 years ago) I still will reach out to my nutritionist who didn't like the idea but went along with me on this. My blood sugar is back in range, I feel like I'm starving sometimes and my weight is going down a little each week and I use Get Healthy U workouts daily.

    on Reply

    I have been intermittent fasting for five months and love it! I have experienced appetite correction and simply am not as hungry as use to be. I no longer mindlessly snack at night and find that I am naturally craving more nutrient rich foods. During intermittent fasting your body does not go into “starvation mode” as this article suggests, no one will starve if they do not eat for 16 hours. Personally, this way of eating is less of a fad diet and more of sustainable lifestyle. I have lost 15 pounds and have for the first time in my life have maintained my loss over the holidays without feeling deprived. I feel like I can continue eating this way for the rest of my life. Please consider reading Delay, Don’t Deny by Gin Stevens or the Obesity Code by Dr. Jason Fung, there is some valuable science behind fasting that may help readers decide if this lifestyle is right for them. This is less of a diet and more of a new relationship with eating.

    on Reply

    There are so many options like fasting, specific diets etc. Most have some scientific claims and proponents who swear by the science. But for me, many feel like there is always a deprivation component. At the ripe old age of 60, I gave up chasing the latest claims to stay in shape as I find the approach that Chris mentions, the easiest to follow without any deprivation.

      on Reply

      Yes Kathy!! You hit it right on the spot. There are so many different health and diet "fads" that come and go but what I always encourage people is to do what is right for your body. What works for one person may not work for another. You have to do what is right for your own health and your own gut. Keep doing you!!

    on Reply

    There are many more benefits to intermittent fasting besides weight loss. After 16 hours of fasting your human growth hormone increases significantly. If you look at the benefits of what your human growth hormone does, you’ll want to increase it. It helps with cell turnover, brain function, and metabolism to name a few. I eat relatively healthy (clean foods) and I exercise (love Chris’s videos) I don’t need to lose weight, but I intermittently fast 16 hours a few days a week just to get the other benefits.

    on Reply

    This is not complete. Hunger doesn't go up with time. Hunger appears when you're used to eating. I've been skipping breakfast for about a month and now I start feeling hungry at twelve o clock. There's studies on this and I think there should be included in this article. On the other hand, the research on fasting on humans is limited and seems to produce more questions than does answers. It has been working for me and those symptoms dissapeared after the first week. Once again I think this article is incomplete. Anyway, it has always been about finding what it works for you... so yeah: no one size fits all.

    on Reply

    I've tried intermittent fasting. I felt great that first time that I did. Each time it got harder to do. I ended up becoming anemic because I became reliant on it for weight loss and I was running for 7 miles one day a week and weight lifting my other days. After becoming so weak from anemia, I decided that it wasn't for me. A healthy diet and exercise are the best way to lose weight and keep it off.

    on Reply

    Hi Chris! I agree with you. Intermittent fasting does not work for me. If I starve myself during the day I would be starving late at night, not be able to sleep so I would scrounge around the fridge and overeat. I would much rather be in control and eat properly during the day. Great article!

    (This will help us personalize your experience so that you can get the best advice possible from us!)
    Skip to content