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    Tapping Into Ancestral Hunger, Part 2: Top Hacks for the 24 Hour Fast

    By Emily Wei, October 1, 2021


    Believe me when I say that the first time I heard of purposefully foregoing food for an entire day, I was more than apprehensive. (I can recall one other time that I’ve done this in my life, and that was after a very regretful trip to the buffet!) After actually fasting for 24 hours, I was pleasantly surprised by both the results of the fast as well as by myself. In part 2 of this blog series on intermittent fasting (IF), we will present the basics of the 24 hour fast, hacks to help you successfully fast, and the top pros and cons of this IF method.

    Not a fasting day? Check out these 10 nutritious recipes to keep you fueled. 

    Calorie restriction = Weight loss

    Brad Pilon, author of Eat Stop Eat, points out that, “Prolonged calorie restriction is the only proven nutritional method of weight loss” [1]. While much confusion surrounds diet trends and recommendations, if such a thing as an irrefutable truth exists in the nutrition world, this fact would be it. In order to lose weight, negative energy balance is required [2]. In other words, you must expend more calories than you consume so you can eat less, exercise more, or better yet, combine the two in order to achieve weight loss.

    For many of us, it’s hard to restrict calories, especially in the long term. I picked the 24 hour fast because I find it easier to completely control myself for one day a week than to give up foods I love day after day. It’s important to note that you should still be eating within reason on the other six days of the week. For example, if you need 2,000 calories a day, eat 2,000 calories six days a week, and fast for one day. Don’t think that you can now eat 4,000 calories six days a week, fast for one day, and still lose weight.

    What the 24 hour fast looks like: Once a week, fast for 24 hours. Once the fasting period passes, proceed with eating as if you had not fasted at all. While Eat Stop Eat suggests fasting 1-2 times per week, I’m not sure how sustainable two days of fasting in a week is for the average person. When I tried fasting for two whole days, I did not find the same success.


    Intermittent Fasting

    But wait, I have some concerns!

    • Won’t my metabolism decrease if I don’t eat for 24 hours? Your metabolism is dependent on your bodyweight, and in particular depends on your lean body mass.  Contrary to popular belief, a number of studies have shown that fasting for less than 72 hours will not affect your basal metabolic rate [3, 4]. In short, no. You won’t slow down your metabolism by fasting for a day.
    • Won’t I lose my hard earned muscle?  When you fast for 24 hours, your body first uses up the sugar stored in your liver for energy, and then relies on fat stores. You’ll actually be burning fat instead of muscle! There is a small catch, however. In order to maintain muscle, you will need to do resistance exercises such as weightlifting.  (This does not have to be on your fast day).

    Now that we’ve cleared the air on those concerns, let’s get into some more detail.

    The rules of the 24 hour fast:

    No foods are off the table

    • During your six feeding days, but you still have to eat within normal means. Eat reasonably and the best you can, but don’t feel restricted.

    No calories during the 24 hour fast, though calorie-free drinks are both allowed and encouraged! 

    • That means there’s no need to forego coffee (five calories of creamer are fine), tea, or even sugar-free gum.

    Break the fast with balance and reason.

    • Break the fast with a regular-sized meal. Though there are benefits to IF beyond calorie restriction alone, you won’t achieve much weight loss if you shovel down a day’s worth of calories each time you break the fast. (You spent the day helping to reset your appetite thermostat. Take advantage of that fact, and remember to reframe your perspective of hunger.)
    • Eat a meal that is balanced with protein, healthy carbs, and fats. Unless you want to feel pretty junky, I wouldn’t recommend breaking the fast with a stack of pancake

    More does not mean better.

    • If you can fast one whole day a week, great.  If you can do this twice a week, the more power to you.  However, limit your IF to a maximum of two whole days a week.

    Keep pumping iron.

    • If you want to maintain muscle, make sure to continue weight training.

    Iron FeedThe #1 way to ease the (hunger) pain

    Fast on a day when you are busy and don’t have any meal obligations, such as a lunch meeting. The first time I tried fasting for 24 hours, I did so on a day that was low-key and boring. I thought it made sense to fast on a day when I was exerting little to no energy and had little to do. Big mistake. While I am not suggesting a fast on marathon day, definitely fast on a day when you are occupied and have less time to obsess over food.

    Pros of the 24 hour fast:

    • It is incredibly simple: There is no complicated meal planning or meal prep involved. For one day, once a week, you stop eating.
    • It’s non-restrictive: The other six days of the week, you go on living your life as normal.
    • It’s maintainable and sustainable: I can see myself fasting for one day out of the week for the rest of my life. Since the success of any diet is largely contingent on whether people can adhere to its rules, success depends on the long-term maintenance of calorie restriction. I believe that many people would be able to practice the 24 hour fast for a very long time.
    • Perceivable cognitive benefits: During the later hours of my fast (think 16-24 hours), I felt like I was seeing the world in a new light. I felt sharp and focused on whatever task was at hand.
    • Excellent appetite regulation: After 24 hours of fasting, my appetite regulation was superb. While I thought that the opposite would occur (and that I would ravenously eat everything in sight), fasting for a day actually helped curb my appetite. I was no hungrier after one day than I sometimes am three hours after a meal.
    • I regained self-control: I constantly talk about how ‘hangry’ I get when I don’t eat, but I realized that food doesn’t control me. I elected to not eat for 24 hours, and I was just fine.
    • You can build-up your tolerance: While it might initially be difficult to fast for 24 hours, it gets easier with practice.
    • You can (and should still) workout: When you fast, your body first uses up the sugar stored in your liver for energy and then relies on fat stores. Muscle glycogen remains available, which means that you still have the ability to exercise in the fasted state. That being said, there’s nothing wrong with taking a workout rest day on your fast day.

    Cons of the 24 hour fast:

    • 24 hours without food can feel very long, especially initially: Many people worry about becoming ‘hypoglycemic’ or getting ‘low blood sugar’ if they don’t eat every couple of hours. This is largely psychological. Research suggests that unless you have a metabolic disease such as drug-treated diabetes, hypoglycemia is rare [5]. During a 24-hour fast, most healthy individuals have the ability to maintain blood glucose in the normal range.
    • Potential headaches: The first time I fasted for a day, my head hurt a bit in the later hours of the fast. However, I didn’t have any problems the second time I fasted, and a combination of slowly increasing your fasting periods and staying hydrated can keep headaches at bay.
    • Beware of post-fast binge-eating: After the first two times I fasted, I binged and broke my fasts with meals of around 1200 calories. Be wary and don’t go crazy breaking the fast. Eat a normal meal, as if you had not fasted at all.
    • Your breath stinks: Despite staying extremely hydrated, this is just inevitable after a day of fasting.
    • Elite athletes and endurance athletes should think twice about the 24 hour fast.  If you are an elite athlete training multiple times a day, are participating in some type of prolonged endurance sport, or are involved in any activity where performance is absolutely essential, the 24 hour fast is likely not right for you [6].

    Changes in weight

    Be patient with the scale. The day after the fast, you will see the number on the scale drop significantly (anywhere from one-half to three pounds) [6]. While a significant amount of this is water weight, you are still losing fat [7]. After feeding normally for a few days, your weight will increase (to not quite baseline) as you regain body water. However, this doesn’t mean that you aren’t losing weight. You are instead dropping fat at a slow, sustainable rate. While the amount of weight lost depends on body size, short term fasting has been shown to help individuals lose around 2% of their initial body weight after about three weeks of fasting [7]. Furthermore, in addition to weight loss, IF can be used to maintain weight loss in the long term.

    Golden rules of IF success:

    • If you decide to try IF, stay in-tune to your body! Fasting may require more adjusting for some than for others; make sure you give your body time to adapt. IF may also not be for everyone, and there is nothing wrong with that.
    • Stay busy.  Don’t torture yourself by sitting on the couch and thinking about food all day. Instead, take some time to clear your head and get your body moving. Go for a walk or catch up with friends.
    • Hydrate, hydrate, and hydrate. Water, tea, coffee… keep the liquids coming.
    • Re-think your hunger.


    My takeaways from the 24 hour fast

    Financially speaking, I have no skin in the IF game. However, as both a self-declared spokesperson for wellness and a serious skeptic about the latest dietary trends, I would be ecstatic if you tried the 24 hour fast. I found IF to not only agree with my lifestyle, but also that it gave me a sense of empowerment.

    As it hasn’t been three months since my last blood test, I can’t yet report on any of my biomarker changes. If the improvements in my mood and appetite regulation are any indication of changes of my InsideTracker results, however, I expect to see improvements in my blood glucose levels, as well as a drop in my InnerAge. What I can say is that I have regained control over my eating habits, have obtained a new perspective on the benefits of ‘hunger’, and have even rediscovered what it feels like to appreciate food. After four rounds of the 24 hour fast, my clothes are even fitting a bit better. While I don’t like feeling restricted, I am plenty willing to fast once a week for the results I desire.

    Stay tuned in for part 3 of the blog series. Next week, I’ll share my experience with the Breakfast Skip, an alternative IF method. In the meantime- what have you got to lose, besides a couple of pounds? 

    Break your fast with these 10 nutritious recipes! 


    [1] Pilon, B. (2012). Eat Stop Eat (5th ed.). Strength Works, Inc.

    [2] Deighton, K., Batterham, R., & Stensel, D. (2014). Appetite and gut peptide responses to exercise and calorie restriction: The effect of modest 2 energy deficits. Appetite, 81, 52-59.

    [3] Verboeket-Van De Venne, W., Westerterp, K., & Kester, A. (1992). Effect of the pattern of food intake on human energy metabolism. British Journal of Nutrition, 70, 103-115.

    [4] Keim, N., & Horn, W. (2012). Restrained Eating Behavior and the Metabolic Response to Dietary Energy Restriction in Women. Obesity, 12(1), 141-149.

    [5] Eckert-Norton, M., & Kirk, S. Non-diabetic Hypoglycemia. The Journal of Clinical Endocrinology & Metabolism.

    [6] Pilon, B. (2012). Eat Stop Eat (5th ed.). Strength Works, Inc.

    [7] Heilbronn, L, et al. (2004). Alternate-day fasting in nonobese subjects: Effects on body weight, body composition, and energy metabolism. The American Journal of Clinical Nutrition, 81, 69-73.


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