My 2 Week 16:8 Intermittent Fasting Experiment

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Over the past several months (since Februrary), I’ve been consistently working out in a fasted state. By the time I finished a workout, I would be starving – especially after intense upper body strength training and HIIT treadmill workouts. Once I got home, I would need to eat almost immediately afterward and struggled fasting for longer than 13-14 hours at a time.

Intermittent Fasting (IF) is very trendy right now and has totally captured my interest; however, despite its recent surge in popularity, the concept has actually been around for years. I remember when I was a kid, my dad used to fast once a week for an entire day (usually on a Wednesday) and I just didn’t understand the rationale. I also had this preconceived myth and visceral fear in my mind that by working out without eating, I would lose muscle mass rather than fat.

I’ve been reading up a lot on the subject and not going to lie, I am totally jumping on the IF bandwagon – there’s so much research out there supporting the immense benefits it provides. I can personally attest to this, as I’m currently at my lowest body fat and best body composition ever as a result of doing my workouts fasted. As a very active person, I was apprehensive to increase my eating window because it comes to a point where it does more harm than good. That being said, I still wanted to push my fasting window up and test out the 16:8 IF method – 16 hours of fasting with an 8-hour feeding window.

I would be remiss if I did not mention that fasting is not for everyone. Following suit with the disclaimer I usually incorporate in my posts, please don’t assume that what worked for me will work for you as well. There are groups of individuals that should not be fasting for extended periods of time – it can be very detrimental to their heath. Especially with women (which I am grouped into), IF may not be as effective as it is with men and can actually cause issues with women’s reproductive systems, including amenorrhea (loss of a period) and fertility issues. I’ll call out a few of these in my post and will also provide links to more resources. Can’t emphasize this enough, but please educate yourself before deciding whether IF is right for you.

I’m an inquisitive being and as an avid runner, I’m always looking for new ways to improve my athletic performance (pace/distance/time) while increasing my energy levels and focus throughout the day. I heard a lot of great things about fasting and therefore, decided to give it a try for a controlled period of time, hoping to log the effects it would have on my body composition and mind.

Introduction to Intermittent Fasting

There’s a bazillion resources out there, but for those that don’t have even the slightest inkling as to what Intermittent Fasting is, this section is for you. I’m going to first pull a quote from James Clear:

“Intermittent Fasting is not a diet. It’s a pattern of eating”

Proponents of the fasting regime have been touting the benefits; more clarity of mind, weight loss, burning fat, reducing insulin levels, and extended longevity of life. I’m not going to get into each of these, but one of the most popular motivators for adopting the IF lifestyle is for weight loss or maintenance.

With smaller eating windows, calorie intake can be limited. On a few of the days where I accidently fasted for 17 or 18 hours for example, then tried to get back on track and eat by 8:00pm, I found it very difficult to hit my calorie count goals. It was inevitable that I would lose weight.

Lastly, there are many different types of IF fasting regimens and windows out there, but in this post, I’m only going to discuss my experience with the 16:8 protocol. I will include a few links to some additional resources at the end of this post. I know I might sound redundant, but again, I highly recommend that you review these resources and seek out alternate information before starting any sort of IF regimen.

The Experiment

The parameters of the experiment were as follows:

  • Fast for 2 full weeks; 16 or more hours of fasting and an 8 hour or less eating window
  • Consume approximately 2,000 – 2,500 calories per day and use the myfitnesspal app to track my food intake. For me and my activity level, this would allow me to maintain my current weight
  • Use the Zero app to keep track of my daily fasts
  • Eating window: 12:00pm – 8:00pm (try to stay consistent at least)
  • No alcohol permitted
  • Try to keep a consistent macro split; 50-protein – 30 carbs – 20 fat

The Experience

In terms of benefits, I didn’t experience a clearer mind or any further weight loss compared to the 12-14 hour fasts I’d been doing over the past several months. I love not having to worry about eating in the AM and waiting for my food to completely digest before hitting the gym. I’ve had so many bad experiences eating too many calories (following the common advice, eat your biggest meal in the morning) before my workout. Eating a bowl of oatmeal with yogurt, berries and some nuts is just too much. I feel bloated and get bad cramping. If I am going to eat prior to a workout, a banana is the only food that will suffice – it provides a slow release of energy.

The first few days took some adjustment. I have the luxury to create my own work schedule, but with that being said, there are some days where I have early morning meetings and need to get my workout done first thing in the morning. I’m talking EARLY (between 5:30-7:30am). I found the 16:8 to be very difficult to maintain with my fluctuating workout schedule.

intermittantfastinghistory

After an early dinner, where I’d eat around 7 or 7:30pm, my sister and I would go for a 1.5-2 hour walk by the water to digest and calm my mind before bed. By the time I got home, I was starving and would end up eating a snack at around 9 or 9:30pm. Waking up at 5:30-6:00am and doing a workout from 8:00am – 10:00am meant that I had 3-3.5 hours left before eating.

There were several days where I couldn’t eat until 1:30-2:00pm and I’m not going to lie, I was grumpy AF. The benefits IF brought dissipated and left me (h)angry. I was not pleasant to be around and my mom can certainly attest to this (thanks for putting up with me Kate, you’re a saint).

From a performance perspective, I noticed zero improvements in pace and power during my runs. In fact, I felt less energetic on several days; where during some fasts, I felt sharp hunger pains in my abdominal area. I didn’t notice much of a difference keeping all other variables consistent. I’m a very active person and work pretty hard at the gym, combining strength and high intensity training (HIIT).

The Results

  • Body weight – Lost 3 lbs
  • Body fat – Lost 2% body fat

Although I did lose weight and body fat whilst doing this experiment, I have to point out that it was probably due to my meticulous calorie and macro counting, as well as cutting out one of my vices in it’s entirety: alcohol consumption.

Words of Caution

While doing research for this experiment, I came across several articles that highlighted a select number of groups that should be very careful or avoid IF entirely.

Pregnant or nursing mothers, the elderly with chronic conditions, children, those struggling with eating disorders, or individuals with either type 1 or type 2 diabetes need to be closely monitored when adopting an IF regimen.

Please read this article if you fit into any of these categories.

And this one.

Conclusion

Although the 16:8 protocol is the most common and sustainable for a lot of people, and research shows it can be particularly beneficial for men, it wasn’t a good fit for me. I might cycle in a few 16:8’s throughout my week, but won’t be able to maintain it for more than that. I can still see the immense benefits of doing fasted workouts, but for me, I need the flexibility to eat when I’m hungry after a workout.

Furthermore, as a woman, fasting for extended periods can be detrimental to my health and negatively affect my reproductive system. Going forward, I am going to pay particularly close attention to my body.

If you decide to give IF a try, write me and let me know what you think.

Additional Resources

Intermittent Fasting Calculator: https://fitnessvolt.com/if-calculator/

Fasting 101 – The Ultimate Beginner’s Guide: https://www.healthline.com/nutrition/intermittent-fasting-guide#effects

Metabolic Effects of Intermittent Fasting: https://www.annualreviews.org/doi/full/10.1146/annurev-nutr-071816-064634

The Beginner’s Guide to Intermittent Fasting: https://jamesclear.com/the-beginners-guide-to-intermittent-fasting

7 Comments

  1. Thanks for sharing your intermittent fasting experience although I’m wondering why you didn’t lose any weight. I lost 14lbs the first month I did IF – credits to https://theblakediet.com/ for their guidance – they’re awesome! But not only have I lost weight ever since I started doing IF, I’ve started to actually feel better too. My joint pains were almost gone and my migraine attacks decreased significantly. I totally swear by IF and would recommend it for anyone out there who wants to feel and look healthier.

  2. I’m concerned as well. You were exercising daily, but you only lost 3 lbs. Well, 1 1/2 lbs. per week ain’t bad, either. I’m back on it after years of keto and rebound weight and cutting out entire food groups. I’m slowly getting back into my fitness programs, but for now, I’m going to keep drinking my wine in the evening, 16:8 fast, and see what happens.

    • Yeah the weight loss wasn’t bad! This experiment felt so long ago…I still incorporate some days with the 16:8 protocol, but it really depends on when I work out and how hungry I am! Flexibility with nutrition timing has worked the best for me. I hope integrating some fasting into your rotation works out for ya! 🙂

  3. Hi Emily and all,
    I think the reason you didn’t lose as much weight as you expected and you had some discomfort is because you didn’t give it long enough. What you need to do is to train your body so that it burns your own fat stores during the fasting period rather than rely on food coming from your stomach. Your body needs to be trained to do this.

    Think of it like training a dog. Suppose you want your pet to “go” twice a day for set hours. You have to be persistent and start gradually. [I don’t think the gradual part is needed for IF]. So, anyway, if you quit training your dog after it follows the schedule one time, then go back to taking him out several times, or switch up the times, he doesn’t know what he’s supposed to be doing. He needs to have clear expectations that he can get used to. Then, when he learns the time he [or she] is supposed to go, he can manage his bladder so he knows when to hold it. Once he’s totally trained, it’s ok if some days you are an hour late or early.

    With IF your body needs to know what it’s supposed to be doing. Let’s say you only eat between 9a and 5 pm. Eventually your body will realize that evening is the time it must fend for itself and it will switch to burning fat during your hours. Otherwise, when you start IF your body starts wondering when you’ve missed a meal: what’s going on? What am I supposed to do? I’ll send hunger messages. Still no food. What is happening? Then when you finally eat, your body is like: no biggie. This has happened before.

    It doesn’t change its expectations and doesn’t change what it does. After a few days it will be like. OK this keeps happening? What am I supposed to do? Should I start the burning calories process? But it’s so hard. It would just be easier if she ate something. Eat something! it will keep saying. Once you’ve trained your body’s metabolism it will figure out, either by the amount of time you haven’t eaten, or by the time of day: Here’s the time I have to fend for myself. Then later: food will be coming soon. I can stop now.

    You will only be burning fat during the time your body expects it will need to fend for itself.

    Also remember, a muscle cell weighs more than a fat sell, so if you lose fat but gain muscle there will be a + – effect.

    • Thank your detailed note! I definitely agree that I didn’t give this experiment long enough for my body to acclimatize. I now use the 16:8 periodically throughout the week, but with my workout schedule I do find it challenging to stick to day-in and day-out! I think fasting in general has immense benefits (more focus, clarity of mind, etc.), but it’s not something I stick to religiously (more so on occasion).

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