The Low Carbohydrate Endurance Exercise Myth

I believe (and the research supports this) that in order to efficiently lose weight that you need to choose low carb foods and follow some sort of carbohydrate restricted diet. The evidence supporting this statement is large and convincing. However, I still read and hear things like:

Low carb diets are the wrong approach to effective weight loss.


Exercise and low carb diets don’t mix.

In fact this could not be any further from the truth. Lower carbohydrate diets are essential for controlling insulin – a key factor in health and weight loss…but you probably already know that.

In regards to exercise and low carbohydrate diets – this is where many people can get confused. Exercising on a low carb diet can be tough if your body is not conditioned to use fat as its primary fuel source.

In the 2 videos above I talk about the different stages of a ketogenic diet (extreme low carbs) and how you need to give you body some time to adapt for not using carbs as a primary fuel source.

Now onto low carb diets and exercise. Two studies published in the early 80’s looked at how very low carbohdyrate diets ( as low as 3% of calories) effected the performance of endurance athletes. You would probably agree with me in saying that the ‘endurance’ community is OBSESSED with carbohydrates. So this should be interesting.


In one study (The Vermont Study) the subjects were put on a low carb diet for 6 weeks and in the second study (The MIT Study) the subjects were put on a low carb diet for 4 weeks. In both studies during the first week the subject complained of being lethargic but when the studies were over the participants did not have any decrease in peak aerobic performance. In the MIT Study is was also determined that essentially all the calories that the athletes were burning during their endurance workouts were from fat.

One of the key points here is that it takes some time for your body to adapt to functioning on low carbs. During that time you may feel lethargic but it goes away. The other point to consider is that the two studies above show that the claim “exercise and low carb diets don’t mix” is just incorrect.

In the Vermont study the subject actually experienced an increase in performance (basically the low carb diets made them better at exercising) but this may have been due to the weight loss that the subject had experienced.

The studies that I mentioned today are pretty old and provide valuable information for people – I have to wonder why their findings are not common knowledge? Any ideas?

Do you have trouble exercising on a low carb diet? Do you exercise better when your carbs are low? Post a comment and let me know what you think.

Please note: I reserve the right to delete comments that are offensive or off-topic.

Leave a Reply

Your email address will not be published. Required fields are marked *

31 thoughts on “The Low Carbohydrate Endurance Exercise Myth

  1. For about 10 months back in 1998-1999 during my divorce, I went on the first phase of Atkins (staying on it the whole time except for cheats) combined with high intensity kickboxing and BJJ sessions (about 6 per week). Most of the time I was fine, but sometimes cravings got the best of me and I’d eat a few high carb meals and/or junk snacks. I usually managed comfortably to maintain low carb 1-2 weeks at a time before a cheat. Didn’t realize at the time that I was unknowingly doing what the professionals call “cycling”. It worked like a charm, and I went from around 330lbs down to 218lbs at my leanest. Unfortunately, I quit pretty much everything using life as an excuse and the weight came back on with a vengeance. Although my performance in training was not affected, this is a lifestyle that one has to commit to or the fat fights back. That’s just my experience.

  2. I did the original PSMF last year where everything was severely restrict – Carb, Fat and Protein. If I exercised I was weak and fatigued then it would take me days to recover. I am assuming your not referring to carb and for that matter calorie reductions that severe? I lost 70 pounds without an ounce of exercise, you can imagine what that produced…a skinny fat person. I still have about 5% body fat to lose but plateaued. I am 5 weeks into a weight training program but I am having trouble finding the right balance to keep the fat melting and having enough energy to sustain the workouts. This seems a bit tricky.

  3. A good friend of mine was using the Atkin’s diet and I would stress to him the importance of carbohydrates. He was doing a lot of cardio as well and had seen tremendous weight loss results, but never wanted to increase his carbohydrate intake.

    Let’s just say that he started listening to me when he almost passed out while running……Not COOL!

  4. I too, am a fan of low carbs for fat loss. However, I prefer to train with intensity, doing MET training circuits and running to bring my muscular legs down. When I do that, I get SEVERELY depleted on very low carbs! I have found I need to incorporate a bit of greek yogurt, berries and lots of veggie carbs to support all of the activity and even still, I know the signs when my body is completely depleted and I need a “carb day.”
    It IS tricky, especially if you train with the intensity as I do. Now if I train heavier and slower and do lower intensity cardio, I can keep carbs super low and feel great. But I tend to stall out quickly after a few weeks of dieting and training this way. Plus I tend put on a lot of size that way and end up “bulkier” . So I prefer the running and MET training with a small amount of low GI carbs. 😉
    Any advice or tweaking is appreciated!

  5. I have found that when my carbs are extremly low, I bonk during long runs (> 4 miles) and my body takes longer to recover. HOWEVER, when I do interval training combined with low carbs, I can keep my intensity up during the short training cycles (around 20 minutes). I like the way I look much more when I’m low carb’ing, my stomach is flatter….that’s always a good thing 🙂

  6. My first question involves the definition of “low carbohydrate”. What percentage of daily calories constitutes “low”? Lower than the government’s current RDA or another figure you are referring to?

    “I believe (and the research supports this) that in order to efficiently lose weight that you need to choose low carb foods and follow some sort of carbohydrate restricted diet.”

    I feel that research supports the idea that you will lose weight if you consume less calories than you burn. You will not lose weight simply but eating low carb foods and/or following a carb restricted diet if you are not in a calorie deficit. I do believe that not all calories are equal, and research has shown moderate to low carb diets are superior to low fat or high carb diets in terms of weight loss. Without a caloric deficit, meaning a person is either consuming less or burning more through exercise, I find it difficult to believe a person can lose weight simply by manipulating macronutrients.

  7. I’ve done significantly low-carb diets a few times (sometimes getting into ketosis). It takes some adapting, but after that there’s no problem exercising (and for long distance, I found that getting into a fat-burning state made for more endurance than having a limited supply of carbs available; of course, I’ve never been competitive at marathon running or the like).

    I don’t believe that low carb is essential for maintaining insulin metabolism. Even for people who have trouble doing that (e.g. me, now, as compared with me in my 20’s), glycemic index and carb timing are more important than total carb quantity.

  8. I tried the zone diet once. This was pretty good. I never been that in shape in my life. It is not like 3% of carbs but it is a lot lower than normal. I had no problem with exercising.


  9. i totally agree with this.. i’ve been on a pretty low carb diet for the past 7 or 8 years… i started while i was in the army, and during that time i ran about 30+ miles a week, did regular PT, and weight lifted HEAVY!…. i never felt tired, i actually felt more energized… my weight has fluctuated since then and i can tell you that its from upping my carbohydrates and then lowering them again… i actually start to feel sick when i take in carbs other than fruits and vegetables… i swear by it

  10. I have been involved with endurance racing for a while now – from long distance cycling to NCAA swimming, triathlon to marathon running. I currently train with Olympic swimmers and Ironman triathletes. I have never met one successful endurance athlete that ate anything close to “low carb”. Reading studies can only take you so far. Whenever the way world class athletes train is in conflict with the way a university study says to train, I find that it is best to trust the training of the world class athletes. I am especially suspicious of the MIT study, in this case. Were the subjects, the athletes, MIT students? I can’t imagine the MIT students would be the most well trained individuals.

  11. I recall that Marc Allen the famous triathlete used the zone diet (40% carbs) in the latter stages of his career and he credited the diet for prolonging it.

    I also recall the Motorola cycling team going on long morning rides on empty stomachs to teach their bodies to use fat as an energy source. I don’t know what their diets consisted of though. I think it would be difficult to convince most endurance athletes to give up their carbs on the whole.

    I think it probably depends on the intensity of the activity more so than the time involved. I have done a few marathon cycling events exceeding 100 miles and at slower speeds could get away with more fats as a fuel but when pushing the pace only carbs would do. Remembering that the digestive system is less efficient when working harder and carbs are definitely easier to digest.

    In summary I think people should experiment in the context of their event/exercise and let their body be the final authority.


  12. I find no drop in performance without carbs. The only carbs I eat are from lots of green veggies (broccoli, cauliflower, asparagus, cabbage, spinach etc, and the occasional apple. I weight train heavy 5 days a week for 1 hour per session and get good pumps and finish the hour feeling great! I usually have a slurp of extra virgin olive oil a few times a day, get a very good one and they taste quite nice. I eat lots of full cream (no milk) cheese and leave the fat on my steak. I never feel bloated anymore and don’t crave junk or bread or pasta etc. I have been eating virtually no carbs for over 6 months, previously low carbs but I cut out wheat and grains as an experiment and feel better for it.
    All I can say is it works for me.


    • Ditto! I seem to have duplicated Alan's regime; I get up at 5:45 during weekdays and hit the weights hard (never heavy squats or deads that early though, I go to the gym one evning per week to get really heavy which in my case means in excess of 450 lb, but I do single leg bulgarian squats @ 8 X 150lbs+) with chains, bands, chins hanging from a heavy rope (you should all try; it's crazy hard). My foodregime seems to be the same as well, and I never get cravings. I can bike for an hour or more, no problem. Sprint several 100 m dash, no problems. High fat, High protein, very low carb. Love it.

    • Ditto! I seem to have duplicated Alan's regime; I get up at 5:45 during weekdays and hit the weights hard (never heavy squats or deads that early though, I go to the gym one evning per week to get really heavy which in my case means in excess of 450 lb, but I do single leg bulgarian squats @ 8 X 150lbs+) with chains, bands, chins hanging from a heavy rope (you should all try; it's crazy hard). My foodregime seems to be the same as well, and I never get cravings. I can bike for an hour or more, no problem. Sprint several 100 m dash, no problems. High fat, High protein, very low carb. Love it.

  13. Ive been doing the Anabolic Diet with great success. Its Low carb high fat 5 days with 12-36 hr carbups best of both worlds. The high fat and carbups are the most important pieces of the puzzle.

  14. Ultimately, it all depends on the person. You can train yourself to work under certain conditions (such as training on a low carb diet), but ones OPTIMAL condition depends on you as an individual.

    For me, I find short term low carbin’ it (for example, eating low carb maybe 4 days out of the week and then moderate and low glycemic carbs the other 3 days) does not affect my athletic performance at all. If anything at all, any problems I have are mental. On a low carb day for example, especially post workout, my inner voices may say ” You know you want to eat an apple with that protein shake,” but I know I won’t pass out if I don’t have one. Essentially, I consider that carb craving to be all in my head and move on with the motivation that in a day or so, I’ll be able to eat carbs again.

    As far as the long term, 7 day a week low carbin’ goes, I find that it messes with my stomach, my recovery time post workout increases and I get DEAD tired all the time after about 3 weeks. When that happens, I know I need to add in a carb up day or at least a carb up meal. And then I usually feel AWESOME for a good few days to a week after that carb up day or meal.

    To caveat both of those scenarios, that is with moderate or average (average for me) amounts of exercise along with that way of eating. I’ve done the low carbin’ when beginning a new routine or beginning to train for something new with increased intensity and it just DOES NOT FLY! My recovery time increases and I am ridiculously tired almost immediately after starting the new workouts. I wonder how consistent or intense the workouts were of the athletes in the studies.

    Again, you could probably get used to training on low carbs, but at what cost? A week, maybe 2 or 3 of crappy workouts? Any athlete I know would not be willing to pay that price. Even the other posters who support a consistent low carb lifestyle for fat loss/weight maintenance copped to breaking their low carb diets periodically.

    What I would say (in conjunction with what I said in my first paragraph) is that low carb eating used as a tool and in a way appropriate for you and your situation is the way to go especially if your goal is fat loss/weight control. We as human beings really don’t need as much carbs as we think we do…… but as athletes, you can’t deny its role in performance.

    For me, I’m more of a carb cycling (between low and moderate amounts of carbs) type of athlete. That’s what I know works for me to keep me slim for my level of fitness–both mentally and physically.

    And I have a question for clarification….was this article meant more to show that carbs are not necessary for good athletic performance? Or to show that athletes train better on low carbs? Or to show that you can lose weight/cut by going low carb and not interfere with one’s training?

  15. While I can train fine on low carbs, I’m not the nicest person in the world when I do. Women have less serontonin in their brains than men and carbs are fairly essential in producing more. So for me, can I perform well and do I lose more fat on a low carb diet? You bet! However, the “me” that is performing well and losing fat is irritable and anxious.

    One small article from amongst many:

  16. Well, also the problem is not just about training, if you are trying to lose some weight, look after a toddler and go to wok and manage a household, sometimes a consistent low carb diet is not doable. carb cycling i think works better.
    i agree with the previous poster, im not the nicest person on a low carb day, when i've also had to work out.

    we're not lab rats, but people who need to go through life doing lots of things.

  17. I'm currently doing low carb… between 20 and 30 carbs a day… first week or so i felt really out of it… but maybe that was from a supplement i was trying at the time… anyway… i find after that first week i feel great and my work outs are better… i don't get as much as a pump on isolation excersizes but those are last anyway after i finish my compund lifts… pluse with low carb and pushing my protein up… i have no real hunger issues and i'm keeping my muscle which is what i want… cause more muscle equals more calories burned as i'm sure every one knows… i'm currently doing a push/pull program from robert dos remedios book "men's health power training" and its a four day program but i've turned it into a six day program… but i've added principals of learned of chad waterburys book also from mens health "huge in a hurry"… and i've been getting good results, keeping muscle mostly and not suffering from over training… which is what i worry about… weights and weight loss are the way to go…

  18. before hitting the weights hard… i ran.. 40 to 50 miles a week… and dropped about 40lbs but alot was muscle… then i went back to weights… gained about ten pounds but was LEANER… and more fit… i still love running but for now i love the iron more… my advice is make carbs low and just live with the small uncomfort of your body getting used to burning fat instead of carbs… and then watch your world change… quick question for mike though… for a male… how low on calories should i go? i think sometimes i go too low.. i added 300 calories of chicken breast yesterday… and woke up and was a pound lighter… i've been fluctuating between 195 and 198 this last week or so… so hopefully you can answer that question for me… and by the way great article on t-nation: deathmatch you vs. your body… i'm guessing its probably posted on here somewhere… i appreciate all you do!:)

  19. Good stuff Mike!

    I would agree! We need to teach the body to burn fat and that is very hard to do when carbs are coming in all the time, increasing insulin and telling the body to use carbs for fuel.

    For endurance events, you want to use FAT as long as possible since the stores of carbs are limited.

    My thoughts are you want the body to be as Metabolically Flexibile as possible–burn fats and carbs are the RIGHT times.

    Rock on
    Mike T Nelson PhD(c)

  20. I do not usually leave responses, but genuinely do love your blog – so thanks for posting and also have a excellent morning

  21. I see a lot of heavy lifters and or super long distance athletes. Neither of which would have a hard time functioning well after adjusted to the no/low carb diet. It is when you mix a 3-5 hour event with 30-40% of which at anaerobic efforts is where the problem begins. You cannot burn fat fast enough to keep up. If you want to slog out a marathon or ultra distance, it seems to be tailored for you, a very long time at a very aerobic effort. My experience is that <2 minute efforts are possible with success but repeated efforts longer than that are compromised.

  22. Actually science does not support what you are claiming here. In fact there is a whole fountain of research saying the exact opposite. For example:

    – Already in 1939 scientists put people on a low, moderate or high carbohydrate diet and after a week checked endurance to exhaustion on a stationary bike. The people on the low carb diet lasted 81 minutes, those on high carb were able to ride for 206 minutes (Christensen EH, Hansen O, Zur Methodik der respiratorischen Quotient-Bestimmungen in Ruhe und bei Arbeit. Skand Arch Physiol 1939, 81:137-71).

    – A 2006 study found that there was an “ergolytic [detrimental] effect of a 7-d high protein diet on self-paced endurance cycling performance”. (Macdermid P, Stannard S. A whey-supplemented, high-protein diet versus a high-carbohydrate diet: effects on endurance cycling performance. Int J Sport Nutr Exerc Metab. 2006 Feb;16(1):65-77).

  23. I have been feeling SLEEPY lately , usually around the 2 hr mark when out mountain biking. I had been trying to eat less carbs, but am beginning to suspect that this may well be the cause… Legs are fine, not really general fatigue, just sleepy??

  24. I am a long distance radonneur in the uk. I have been on a 90calories from fat diet for three months. I supplement with sodium and pottassium . I have completed a super radonneur series fuelled only by nuun electrolyte drink for the entirety of every ride (200km, 300km, 400km, 600km rides) . Have maintained full CNS FUnction throughout every ride. Plan a 1200km ride in the summer. Done properly this diet gives SERIOUS endurance advantages.

  25. The newer studies are being done now by Jeff Volek. For “sprint” athletes some carbs are needed ingested around the event, but training can be done low carb. For any kind of endurance sport, being fat adapted is king. There will be no question about it as the years go by.
    So much bro-science in blog comments. Facts: daily intake of carbs do not work well for over 70% of people.