Each time a new diet trend comes out, I find my eyes involuntarily rolling in to my skull and a sigh escaping my lips.
What can I say, after being feed plastic cheese because it was non-fat during the era of fat will make you fat, I’m now a skeptic. I also worry about diets that cut out food groups becoming so strict they seem impossible to follow for a lifetime.
Which is why when Intermittent Fasting first showed up under the clever program of eat all you want from 12-8 everyday without counting calories, I wanted to burn another diet book.
BUT luckily a few smart people pulled out the real nuggets of gold and turned it in to something that can actually be used. I’ve been asked if it’s the best diet for runners to lose weight, so I wanted to get in to the details here.
What is Intermittent Fasting?
Intermittent fasting is a style of eating that limits you to eating windows of 12, 10, 8 or 5 hour windows throughout the day.
For example, you might finish dinner at 7PM and then not eat again until 9AM the following day to create a 14 hour period of fasting.
The goal is to maintain overall caloric intake, simply eating in less hours per day, in order to to create conditions of fasting without going to extremes.
I don’t really care for the source of this graphic, but it does a good job of visually showcasing the benefits of Intermittent Fasting.
Benefits of Intermittent Fasting
I love that there have been a number of actual studies on this and show the benefits go far beyond weight loss, though that’s surely what gets many people started.
- Insulin levels: Blood levels of insulin drop, which facilitates fat burning and can help to prevent Type 2 Diabetes
- Human growth hormone: Higher levels of HGH facilitate fat burning and muscle gain, it’s shown they could increase up to 5 times
- Reduced Inflammation: During fasting the body handles a lot of cellular repair and reduces inflammation
- Happy Heart: Lowers LDL, blood pressure and blood sugar (heart attacks are the number 1 killer of women, so this is huge!)
- Better brains: Studies in mice have shown increased creation of new cells and hormones that are linked to prevention of depression and it could help prevent Alzheimer’s!
Another factor of Intermittent Fasting is doing your cardio in a fasted state. Since this is such a large topic, I covered the pro’s and con’s in a separate post so you can decide what works best for you.
James Clear gives a great description for those looking to the weight loss goal:
Well, most notably, it’s a great way to get lean without going on a crazy diet or cutting your calories down to nothing. In fact, most of the time you’ll try to keep your calories the same when you start intermittent fasting. (Most people eat bigger meals during a shorter time frame.) Additionally, intermittent fasting is a good way to keep muscle mass on while getting lean.
For distance runners, I think those points are key!!
Can intermittent fasting work during marathon training?
In marathon training, many runners often find they begin to lose muscle mass and of course if they’re doing it while trying to lose weight they’re attempting to cut calories, thus feeling all around fatigued and hating the miles.
The lack of calories prior to a run can actually result in not being able to workout as hard or run as far. Read that fasted cardio post for more.
But additionally, there is science that when women restricting their eating for too long (yes even in a given day, not just a diet), the body increases cortisol. We know this stress hormone leads to holding on to weight around our middle, but it also hinders your training progress! 
MY EXPERIENCE WITH INTERMITTENT FASTING
I am a snacker, this isn’t an all together bad thing, but if I’m not paying attention it can get away from me.
Suddenly my morning routine which had been nothing but a little pre-workout was including a spoonful of nut butter and half a Clif bar. My evening finished with a satisfying dinner around 6:30, but then as David ate later around 7:30 I’d feel compelled to munch on some cereal or chocolate though I was certainly not hungry.
Nothing major and nothing really wrong with any of it, but it also wasn’t getting me to my goals.
I decided I would start by doing 12 hours of fasting, that seemed easy enough between sleeping and such. Immediately that’s what opened my eyes to those extra little bites I was taking when not hungry!
- I am less hungry (which meant I had to focus on getting in the right calories)
- I have less sugar cravings
- I eliminated a lot of unnecessary snacking (let’s be honest that’s not usually veggies)
- I am seeing what looks like muscle gain finally
- I have lost the weight that my hormonal shifts caused (also attribute to cutting dairy and eggs)
I am NOT as strict as many people are (read some of why below).
Which is to stay that if we have dinner at a friends and don’t finish til 8PM, but I find myself starving at 7 AM I will eat….or if I am simply not hungry around the time I should eat dinner because it’s the end of my “window” I don’t force it.
It’s important to remember to still listen to your hunger signals and stick to healthy food choices. Unfortunately like many things, people have found ways to use this fasting style of eating to simply consume more crappy foods. But crappy foods don’t make for good running! 
INTERMITTENT FASTING FOR WOMEN CAUTIONS
Intermittent fasting works differently in men and women. There are some things that women (especially my distance running ladies) need to be aware of and of course as with ANY style of eating, it’s simply not right for everyone.
When taken to extreme it’s the frequent cause of the female triad, as noted by Bullet Proof Exec:
So the problems of caloric restriction, excess cardio, and intermittent fasting are related and express themselves in exhaustion, adrenal fatigue, and hormone problems, in both women and men, but women are more sensitive to these effects than men and feel the problems first.
My tips for doing it healthy as a runner!
Protein Powder
This is one of the reasons, that I take in a little bit of protein powder prior to my morning runs. It’s not enough to stop the fasting benefits, but it does signal my brain that we aren’t in trouble there is no famine.
Alternate Days
Additionally, you don’t need to do the fast for the full 14 hours everyday, you can alternate based on your training.
Prior to long runs, I will break the fast at 10 hours because I know that there’s long term benefits to getting in even 100-200 calories before those miles. Namely I won’t be starving at the end, I won’t use that as a reason to stop and it actually helps to kickstart the recovery process.
Women who have issues with menstrual cycles or wake up frequently at night are not encouraged to try this! It seems to make their bodily stress worse. In most cases, it appears to be due largely to cutting calories, but there is also a number of studies showing that a little carbohydrate before bed can help people sleep and that would not be available here.
How can women try this?
– Try fasting 14 hours 3 days a week
– Add a 4th day if you feel good
– Focus on 12 hours most days
As noted above it has decreased my appetite, which is fairly common. Since my goal is building muscle, losing a little fat, not actually dropping weight I have been paying attention to my total protein and calories to ensure I’m not creating a big deficit.
This is KEY for female distance runners to ensure you don’t cause long term issues.
Have you tried Intermittent Fasting?
What do you think of the idea?
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Megan @ Skinny Fitalicious says
I’ve read a lot about this in nutrition school. Some of the studies related to sports conditioning are fascinating. One in particular showed people fasting 30 or more days and improving their marathon times. I don’t understand how that’s possible but that’s what it showed & the people claimed to feel amazing.
RunToTheFinish says
Yes I agree! I've seen some seriously long term fasting and that I totally can't do! A day without foods sounds awful and they manage to go weeks!
wendy says
I don't know about doing this "formally" but I do run on an empty stomach most mornings. I find that I actually run better if I don't eat before (unless I'm going long). I know enough about metabolism to be dangerous, and if you realize that when you eat you release insulin, well, it just makes sense. Supposedly running on empty helps you become more efficient at mobilizing stored glycogen. But fasting? I can't do that.
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RunToTheFinish says
You fast every night and are basically doing this by going from the time you got to sleep until post run sans eating.
mapsley says
I make it a practice to stop eating by 7:00PM and not eat again for at least 12 hours. It works for me. But I started doing that 13 years ago after my son was born, and it helped lose some of that baby weight. It's just something that has worked for me along the way. I'm an early morning exerciser…..most days running, and so I often do a fasted workout in the morning. The important thing is just finding what works for your unique body and unique training needs.
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@V_Nutrition says
I've read some studies on intermittent fasting and it does seem to be a viable option for many people. I have been thinking of trying it myself – I think I will now after reading your post! Great info, thanks!
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Tricia @ MissSippipiddlin says
I have been paying more and more attention to this. Great info all right here! It’s usually closer to 9 before I eat breakfast so my real challenge is to be done with dinner by 7. Now that is a challenge around me!
I have dropped a few pounds the last few weeks andI believe it is due to participating in a run streak where I am every morning at least getting in 1-3 miles on an empty stomach. Thats really all I’ve done different.
Michelle says
Thanks for that great synopsis! I've been reading a lot about intermittent fasting lately and wondering what the benefits were. Interesting, but I definitely agree with your take on it.
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Elle says
I do this most days … 12 hours but I don’t workout or run unless I eat a bit first. I bonk and feel sick otherwise.
[email protected] says
Intermittent fasting is a conscious decision to skip certain meals. My last meal in night is at 8PM and I also does not eat anything till 9AM morning. Although I have a great metabolism, but I do some things as precautionary. I found Intermittent fasting the best way of dieting by far. And yes, I like your advice for women regarding intermittent and definitely going to note down. :-)
Nutrition Fox says
I kind of find it hard to fast even a couple of days or two, i feel like I’m passing out! But regardless you have a very good valid point here. Thanks for the information!
Amanda - RunToTheFinish says
That’s the point of intermittent fasting, you aren’t going days without food. As noted above it’s about selecting a time frame each day for not eating to allow for better digestion, etc.
Travis says
Interesting post! I’ve been reading up on intermittent fasting and I might just give it a go when I start conditioning for my next marathon. Thanks for sharing this, your post made me understand the concept a lot better!
Steve says
This is a great take on intermittent fasting. My results have been fantastic! I dont eat till about 4pm each day and when i do, the first thing is protein, blueberries and porridge with some peanut butter.
Absolute heaven after a long fast. Its great for discipline as well as being able to work better in my opinion
Johnathan says
Hi Amanda, great post. I have practiced fasting a few times. I have done 7 day, 10 day and 14 day fast. These were straight water fast. After undergoing these types of fast, I think I will soon start to do intermittent fasting as part of my regular week.
Thanks,
Katharina says
Hey, thank you for your post! I just came across your blog when looking for experiences about intermittent fasting in combination with running on Google. I am a half marathon runner and first heard about IF in a documentation about fasting in general. In contrast to all the other diets, there were scientists and doctors talking about the health benefits of IF on heart and brain. I am a molecular biologist myself, so I immediately looked up scientific literature and was amazed about how many papers have been published about IF! Anyways, I wanted to try it out myself, mainly because I like to eat and although I eat healthy, I have troubles maintaining my weight, as I manage to eat more than I burn even with 5 days of training per week and a healthy diet. I am fasting for two days a week now for two months and it is great. I never thought I could do a whole day without food, but it works better than I have thought (well, I allow myself a Starbucks Cappuccino and some fruits on the afternoon and before going to bed, adding up to about 300 – 500 kcal). I counted calories in the beginning and although I do not restrict myself on the eating days and up with about 3000 kcal/day, over a week the calory intake and outtake is quite balanced, sometimes with a small deficit of about 500 – 1000 kcal. Another big advantage is that I do not have problems anymore with getting in enough proteins with my mainly plant-based diet, as now I can allow myself a “snack” of 100g Cashew nuts.
However, it is still a bit hard for me to fit IF into my training schedule. I usually fast on rest days, but if I do workout on those days, I have small meals before and after, roughly balancing the burned calories. It works well, but as my rest days are usually after Long Jog/competition/Intervall Trainings, I wonder, whether the fasting might be detrimental to my recovery? Do you have any experience in that? I also have no idea, how long it takes the muscles to recover on a molecular level and if there is enough protein available on a fast day? I would love to hear your thoughts about this! How do you arrange training and fasting?
Debbie says
Apparently I’ve been doing this without even realizing! I rarely eat after dinner or before a shorter run, unless I have to work early. This is great information. Like you, I tend to scoff at the new diets that suddenly become popular.
Cindy says
I started intermittent fasting a year ago but not eating good and then started doing it with good food and saw great reasults. I FAST 7-12 everyday and do all my runs and races fasted. 3 half marathons last year fasted except for bcaas & electrolytes. It’s the only lifestyle for me now. No gaining weight since not carbo loading anymore and no inflammation. I love it!!!