View Full Version : Low Carb Diet The Endurance Athlete

March 23rd, 2007, 09:30 AM
Anyone have any experience trying out a low carb diet while doing endurance training?

I'll share my story, and see if sounds familiar. Last year, while training for a 10 mile road race, I decided to try and drop some additional weight by going on a short-term low carb diet. I was out for a easy five mile run roughly three days into it, and actually had to stop running! I could not get my heart rate to come down and ended up walking/running the last mile...

Never happened before to me, and never since. I've talked to several power athletes (weights, etc.) who claim not to have that problem, so I'm wondering if it is just us endurance people. I went back to the normal diet the next day and was fine.

Anybody else have a similar experience?

March 23rd, 2007, 10:42 AM

Never had it happen to me - but never tried low carb.

The raised heart rate could have been be due to glycogen depletion - like hitting the wall in the marathon (ouch - been there - done that!).

If you had been depleting your muscle glycogen stores and not replacing it because of the low carb diet, your body may have had to switch to burning fat.

How was your perceived effort when your heart rate went way up?
If you were burning fat, you would probably have been feeling like s**t!
If you felt fine - but with a high heart rate - not sure if this would have been the cause.


March 23rd, 2007, 01:05 PM
Satori - I felt like absolute h*ll, so that must have been it.

March 23rd, 2007, 04:53 PM

Sounds like you "bonked"

Classic glycogen depletion symptoms.
Several days training with little or no carbs would do it!
Not fun! :upset:

Thats why marathon runners carbo load before races.

Have fun


March 23rd, 2007, 05:14 PM

Just re-read my posts and sorry - not makiing myself very clear.

I have not had this happen to me because of low fat diet.
But I HAVE had it happen to me due to trying to run marathons without putting in enough base mileage and endurance training.
It is probably the worst I have ever felt during any race - marathons, half marathons, or triathlons.

If you are an endurance athlete - either a distance cyclist or a long distance runner - this can become a major issue.
Even a well trained marathon runner needs to train to avoid bonking as normal or poorly trained muscles can normally only store enough glycogen for 18 to 20 miles of running.
Not sure what this equates to in cycling.

Endurance training helps the body to more efficiently utilise fat as an energy source. The more distance and base mileage you do - the better it gets.
The danger is if you either try to do high mileage endurance racing of whatever sort with insufficient base OR if you DO have a good base, but you do deplete your glycogen stores by over training and not eating enough carbs.

Hope that is more clear.

here is a link I found good for base building info


I always had a problem having the patience to build a good base!

The article is really aimed at triathletes but same principles apply to all endurance sports.

I am sure you already know all this - but just in case!


March 27th, 2007, 01:59 PM

Sorry for the late reply...I just started branching out of the general discussion forum! :)

Last Spring I started the South beach diet (NO carbs fo rthe first 2 weeks) during soccer season. Started on a Monday, and noticed during the week that I was having a hard time running in general (ran out of energy quickly, chalked it up to lack of motivation). The first game I played at that time I noticed a serious drop in my ability to run (just couldn't make my legs move properly during the second half), and was sore & sick as H*ll that afternoon. I assumed it was from the lack of carbs and went off that part of the diet for he rest of the season...never experienced that again.

I know soccer's not the same as road race training, but sounds like a similar experience.


April 2nd, 2007, 09:21 AM
having just come off atkins again, i can identify.
i am not an endurance athlete but a while ago I used to do spinning classes regularly - when i dd this on first 2 weeks of atkins i had no energy, hot flushes,muscles felt weak and i felt faint - this time i was out of breath walking on atkins.
I'm now eating carbs again and feeling great and like i could go for a run again - for me low carb is good to get weight off quickly for a short period of time.
others feel great on low carb diet - i'm not one of them!

May 21st, 2007, 01:31 AM
I also found the same thing i.e total lack of energy and exhaustion performing my usual training for a half marathon whilst following atkins diet. I feel it is just not sustainable for those who have a reasonably heavy exercise scehdule. Not to mention brain fog and irritability!

May 21st, 2007, 04:09 PM
there may be some misunderstandings of the Atkins diet here. The first few weeks your body will be going though some definate chages and I wouldn't judge the diet based on that initial phase. There are many endurance and other types of athletes that do quite well on it. Brain fog and irritability are symptoms of an intestinal candida overgrowth (something that can easily happen on a higher carb diet) when you are on a healthy diet like Atkins those bacteria are being killed off and you will feel the effects of the toxins breaking down and leaving the body...BUT it's temporary. Atkins is a complex and easily misunderstood diet system and I'd say the most mis-quoted diet in the history of mankind! anyway we all find what works for us in the longterm...keep an open mind and a good journal.