Running In A Carb-Depleted State: Good Training?

by Angela (Oh She Glows) on August 8, 2009

Today I will be talking about another ‘New Rule’ from the ‘The Rules: Revisited’ Runner’s World article that I featured the other day.


Today’s topic: Carbs and training

Old rule:

Emphasize carbs when you’re marathon training, especially before and during long runs.

New Rule:

Do some long runs in a carb-depleted state

In this part of the article, Bob Cooper talks about how carbs have been the focus of nutrition advice for runners for the past several decades. Since carbs are the most readily available fuel source for our bodies, it makes sense to consume lots of them prior to a race or long duration activity. However, exercise physiologist, Greg McMillian, says that runners should do some long runs in a carb-depleted state. In other words, don’t load up on carbs prior to some of your long training runs.

That doesn’t exactly sound like a fun run in the park now does it? Greg is trying to take away one of the things I love about running; being able to stuff my face around the clock! ;)

Greg explains his theory:

“You need to teach your body to operate with low glucose stores because that’s what you’ll be facing in the later miles of a marathon.”

He suggests that runners skip their carbs before and during long runs to improve the body’s ability to burn fat and store glycogen, which is pivotal in long bouts of intense exercise.

“By not taking in carbs or energy gels during the run, you’re giving your body no choice but to go to fat-burning. You will feel fatigued near the end, but that’s necessary if you want to get stronger.”

Greg suggests not to go cold turkey on carbs with your next 20-mile run. He says to wean yourself off of carbs by consuming them less and less before and during long runs to train your body to manage without them.



When I first started running on a regular basis last Spring/Summer 2008, I always ran on an empty stomach. Otherwise, I would find myself getting really bad stomach cramps. The downside of this? I couldn’t run very far without feeling really drained and fatigued. Since doing more research on running, I have since switched over to the ‘carb loading’ camp, by making sure that I do fuel up, at least modestly, before my runs. And for whatever reason I find that I don’t suffer from running cramps anymore. Perhaps, my body has just adapted better to running now. I find that I am able to go longer distances when I fuel up beforehand and not ‘hit the wall’.

The thought of doing my long runs without carbs seems quite daunting to me. And I still question Greg’s approach. While I can see that it may train the body to use other fuel sources, I find myself asking what the point of that is.

Runners have access to plenty of carbs during races, such as Gatorade, energy gels, and chews, so is it really necessary to endure these long intense runs with no carbohydrate fuel? I mean, this may be obvious, but isn’t that what it’s there for?

During my 10 miler, I took Gatorade by mistake at the 2nd or 3rd water station and I was worried how my body would react. Well, I was thrilled to find that the Gatorade gave me a huge energy boost, much more than regular H20 did. And so at each water station thereafter I drank my carbs. I know my performance was enhanced because I felt a little kick to my step after drinking about 4oz every station.

The article doesn’t state any hard evidence of Greg’s theory, nor does it suggest what we should be eating instead of carbs. I would love to see some research on this topic. I know that protein can be very hard on the stomach prior to runs (it is hard to digest) so I always personally avoid protein and also fibre before a run. So what’s left if I also don’t consume carbs? Personally, I would love to pick Greg’s brain a little more on this subject as I find the article didn’t quite convince me enough to forgo my fuel. I would also love to hear from more experienced runner’s- have you ever given this a try and did it improve your running?

What do you think of Greg’s theory? Would you try it out?


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{ 27 comments… read them below or add one }

Juicy Jessy August 8, 2009 at 12:34 pm

i run a LOT without having eaten. First thing in the morning. Sometimes before work; only an hour. But often also in the weekend and then I have more time. Last week I completed 14K on an empty stomach, this morning I went to the forest by bike (about 17mins) ran 7K and then took another way back, about 25mins.

I must say that I don’t have any problems working out on an empty stomach; even though I do get hungry at work real fast when for some reason I wasn’t able to eat breakfast.

I find running takes away my hunger, rather than causing it. When I run after work; I don’t feel like eating when I get home either; but after running I always eat; to help build up muscle tissue.

Interesting that it works so differently for different people, my boyfriend has the same issues as you do, he feels less energetic when he hasn’t eaten enough.

I would never ever try running a race without eating however. If I want to run real fast; I eat whole wheat bread with a banana and some nutella :-) that works best 2 to 3 hours before the race :-)


Jenn Eats Nutritiously Now August 8, 2009 at 1:33 pm

I can only do about 60 minutes of activity on an empty stomach before I really need some fuel. I think his theory really makes a good point, though.


Amy August 8, 2009 at 1:51 pm

Ouch. Not sure I agree with this one at all.

I’m like you in the sense that food and running don’t really mix all that well. But, overtime I’ve found a combination of protein + carbs that works well for me. Before a long run, I eat PB and Banana on a slice or 2 of toast.

That being said, when I run my short fast runs during the evenings (5 or 6k)usually I don’t eat before going running and I’m just fine.

I guess it all depends on the individual.

I am a firm believer that carbs = energy and are ESSENTIAL for runners. I’m pretty sure I would die without carbs. After all, I think sometimes the only reason I run is so that I can eat! :)


Nicole- Chasing Blue August 8, 2009 at 3:53 pm

I haven’t carbloaded for any of my runs. A wise runner friend of mine said that most people eat enough carbs to get them through 15 miles. I’ve only done up to the Half Marathon distance so I just haven’t felt like I’ve needed to take the time to do so! Most research says carb loading isn’t necessary unless the run is over 90 minutes.

For me, being properly hydrated is a bigger key to my running success!


Sana August 8, 2009 at 3:59 pm

Yikes, I am very guilty of not eating before working out, its a good thing I have my earphones on so I don’t hear my angry tummy.


Ashley August 8, 2009 at 4:22 pm

I’m not a runner, but in no way does that sound healthy for the body. I’d like to hear multiple doctors opinions on that subject.


Kailey (PB Swirl) August 8, 2009 at 5:30 pm

in all honesty I would never ever try this. Like you, I need my carbs or I can only do 2 miles without feeling worn out.


Karen August 8, 2009 at 5:30 pm

That’s actually very sound advice, and is followed by many endurance athletes–especially at the marathon/ultramarathon level. It trains the body to become more efficient, so that when race time comes around we perform optimally (and carb load, take gels etc). It’s not unhealthy, just a bit (often very) uncomfortable during training. It takes a lot more energy to burn fat as opposed to glycogen, so it’s pretty common to “hit the wall” when training without carbs as fuel. But when the body gets used to it, then it’s much better prepared during the second half of the marathon (or ultra) when the glycogen stores run out.


Angela (Oh She Glows) August 8, 2009 at 6:23 pm

Karen- If a runner was taking in proper fuel such as energy drinks/gels at regular periods, wouldn’t this prevent the glycogen stores from running out though? That is the only part I don’t get. ~A


Mike October 7, 2009 at 1:08 am

No, you can eat all the carbs you want and still deplete your glycogen. Your body can only convert the carbs to glycogen at a fixed rate, eventually body fat will have to be utilized.


Kim August 8, 2009 at 7:40 pm

I read this article the other day (coincidnentally while I was running 8 miles on the treadmill). I am not sure I am ready to jump on this boat. I have been having energy issues after my long runs of 8 miles+, but not during. I can’t see forgoing the carbs before and then having nothing mid-run. I don’t have a lot of body fat to draw from, so maybe that is the reason? Not complaining, but I don’t think that his method would be beneficial to everyone out there.

I would be interested in more info on this subject, though.


Madelin @ What is for breakfast? August 8, 2009 at 8:34 pm

Wow some mixed opinions on this one! I don’t tend to “load up” though I eat quite a lot of carbs each day anyway and as I run during the day or in the evening I have usually had some form of complex carbs at least 3 hours earlier. I suppose you could say that is carb loading then…


The Running Yogini August 8, 2009 at 9:18 pm

I’ve played with different ways of eating over the year and I really feel like its best (for me) to just eat a healthy balanced meal before runs. Some days I eat a higher percentage of carbs and some days I eat a lower percentage of carbs, but my body learns to adjust. If you follow a proper training plan, then your preparation will carry you through the race and you don’t need to worry about carb loading vs. carb avoiding. Your adrenaline will help you at the end and if you need a little kick than enjoy your gatorade! I LOVE the extra energy I get from Gatorade on a race day!


heather August 8, 2009 at 9:25 pm

I might do this if I could see scientific evidence that training in carb-deprived states improves the body’s ability to run in carb-deprived states. He doesn’t present any evidence that it does; he just seems to make a logical leap that it should. That’s not enough for me.

I used to run early in the mornings, with nothing in my stomach. I stopped because I found that running that way was too difficult on my body and wasn’t leading to any improvements in my ability to run faster or longer. I wasn’t able to increase my mileage because I wasn’t improving. Once I switched to running in the afternoons or at night, after getting some carbohydrates in me, my runs became way easier and I was able to increase my mileage and speed at a much faster rate. So my un-scientific experience has been that running without fuel doesn’t train your body to run without fuel. If it did, my un-fueled runs would have gotten easier over time, and they never did.

As for your question–would someone hit the wall if they were taking in enough carbs over the course of the race?–the answer is no. If you continue to consume a sufficient about of carbs during the race, you should be fine. The question is . . . what’s a sufficient amount of carbs? I don’t know the answer, but I suspect that a little cup of Gatorade every mile isn’t going to be enough.


Pam (Highway to Health) August 8, 2009 at 9:31 pm

Hmmm I never really thought of it like this. I might do this on a couple of my shorter runs once I start to get into my training plan but I can’t imagine doing it on a long run. I can’t eat too much before my runs anyway so I don’t know if it will make a huge difference. Since I have a few lbs to lose I’m not opposed to this!


Alex August 8, 2009 at 10:14 pm

Good for you for being a savvy reader, and not just accepting every theory that is proposed.

While Greg’s theory does seem to make sense, I also agree with your question, “What’s the point?”

If YOU feel awful without eating something, then don’t do it! Remember that what works for one person is not necessarily right for another.

Take care, Angela!


Jessica August 8, 2009 at 10:28 pm

This is a great post. Def avoiding protein and fiber before a run … I like having a banana. I like to avoid fats before a run too because they make me feel sluggish.


Randi August 9, 2009 at 1:43 am

I’m really shocked at some of the responses on here. I mean, have some of you run for 4-5 hours straight before in training? And you think its acceptable not to intake any carbs for 5 straight hours of running? I’m pretty sure this article was written for people running ~2 hours in training. Maybe I’m the only one who thinks this is crazy. But for my pace and 4+ hour training runs, this is would not only be impossible but dangerous!


Ruby August 9, 2009 at 8:48 am

I agree I’d want to read more research on this – it sounds logical, but not everything that sounds logical is actually true. I think running on empty sometimes happens anyway, and those are great training moments to keep going mentally! My PT reminded me that not all your runs will be perfect under perfect conditions, so embrace the tough ones and tough them out – the easier runs will feel even better. So yeah, I think maybe people need not be so obsessed over carbs, but everyone should do what works for them. Also, running should be pretty enjoyable – forced fatigue does not sound like fun!


Lara August 9, 2009 at 12:43 pm

The problem is the body won’t turn to fat for energy stores automatically. Often it will turn to muscle tissue too so you wind up burning muscle (this can happen even when workout for 45-60 mins on empty stomach). I think most people who go out and run for 45-60 minutes don’t need to “carb load”. A meal or snack is one thing if it helps energy levels but I know people who use their running as an “excuse” to go overboard. You don’t need to carbload before running a few miles LOL


Karen August 9, 2009 at 4:36 pm

Angela – sorry for the late reply. :) The reason is that during long races, carbs/glycogen are consumed by the body faster than they can taken in/absorbed, and once the glycogen stores run out, your performance will suffer no matter what you try to take in at that point. It’s happened to me and was no fun! I should add that the school of thought that favors carb depletion in training doesn’t mean Atkins diet, or running 4-5 hours with no carbs at all. That would be impossible. The point is to limit “carb loading” and use gels far less frequently during certain periods of training to help make our bodies more efficient.

Here is a decent article that references scientific studies to back up the theory.


Kerri August 11, 2009 at 10:14 am

The only way I have semi-trained with this theory is in terms of GU and Gatorade. When I trained for my marathon I would only drink h20 on my long runs, and take 1/2 GU packets. Because I knew my stomach could handle more amounts (due to previous experiences…) I would then switch to Gatorade and full GU packets on race day. Knowing my body could handle the intensity on less fuel made my extra power bursts propel me to the next level. I never went without carbs, however, and especially not in my pre or post run fueling…to me that’s just a recipe for disaster. Limiting my carbs while actually running … however… did give me both a physical and mental boost!

-Kerri from Enzymatic Therapy


SOPhos August 24, 2009 at 11:53 am

I tried to do both- with and without carb loading- without carbs before a workout, I hit the wall after 3 miles. With carbs, I could run for up to 13 miles. I think for me- it’s very psychological..when I have carbs, my mind is saying ‘look, you’ve no excuse to be feeling tired, you’ve got the energy’ whereas when I don’t eat anything, my mind is saying ‘Awww poor you- you must be really hungry!!!!!’ :)


Paul September 16, 2013 at 11:18 am

This has worked well for me. I am up to 2 hours (about 12 miles) on my long steady steady state runs now with no problems. I had to start slowly cutting carbs to work my way up to this point. Just like building any adaptation in the body, you have to be patient and do just a little at a time. If you just go out and run in this state you will not get very far. The body has to have time to adapt.


Marty September 28, 2013 at 4:57 pm

Back in the 70s and 80s, many runners did a moderately long run about a week before their marathon, followed by 3 days of low carb , then 3 days of high carb. The muscles become more sensitive to storing glycogen during the depletion phase and become”supercompensated” during the carb loading phase. I see no point to depleting before a long run – the long run itself is depleting. I can tell you that this worked very well. The idea that you would want to burn slow and inefficient fats results in slow running.


Paul November 5, 2013 at 12:40 pm

This article

references one study at an overseas institute. I have not really searched hard for anymore research. I think one key is…this is only done during a couple of long runs, 10 to 8 weeks out from your marathon. In between those runs you are eating carbs out your ying yang to refuel. AND it is for SLOW runs only, not fast finishes or races. McMillan’s article is quoted above, but if you read the entire article, he says it is not for everyone and to make sure and carb up after and to NOT do this for long fast finishes and not to run more than 3 hours.

For me, I am willing to try new methods at least once to see if they benefit me any….if not I toss it and chalk it up to experience. I think that is pretty much what has made me improve in my marathons is just experimenting. And everyone is not going to be the same. I think if you run to enjoy eating, then enjoy eating!!! I run because I enjoy competing with myself to see how much farther I can take my performance.


Jess February 10, 2016 at 12:11 pm

Have tried this yesterday. I think that the key to tap on the fat as fuel is to do longer warm-ups. I covered the same distance but with somewhat increased time, about 3minutes.. Perceived exertion was pretty low, perhaps about 11 or 12, did not feel any soreness and felt good. I only ran faster towards the last 10minutes. RPE was usually 13 to 14 when I cover the same distance and load up with carbs prior to running. When you want to run fast, i believe that’s when the sugar will be useful. To each his own. What works for one may not work for the other. Maybe when we’re doing easy runs, this works good. I’ll try it on my tempo run and see how it works.


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