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How Does Intermittent Fasting Affect Carb Loading?

Posted by Scott K. Patient Expert

Time for Carb Loading

It’s time to look at another Skribit question and give a quick answer. The question I’m answering today is:

Every other day fasting and its impact on how often to “carb load” when on a ketogenic diet.

I’m going to go ahead and acknowledge that I don’t carb load, so my answer isn’t from an “insider’s perspective”. My version of a carb load entails adding in a sweet potato after one of my more grueling workouts, but beyond that, I figure that my normal carbohydrate intake will refill my muscles before the next rough workout. But this question is obviously on quite a few people’s minds as it has 82 votes (or one person is voting over and over again if that’s possible).

Just for information’s sake, let’s look at the three main versions of the standard carb load.(1) The original carb load was developed by Gunvar Ahlborg, a Swedish scientist, in 1967. His theory was to deplete the glycogen (the body’s stored form of carbohydrate) stores prior to the carb load, starting about a week before the event with three days of low carbohydrate intake (about 10% of total calories). Then the next three days was a carbohydrate intake of about 90% of calories with a reduction in exercise intensity.

In the 80s, a modified regimen was developed, eliminating the depletion phase and increasing carbohydrates to 70% of intake for three days, also with decreased training. This is the most popular regimen today. Finally, a new regimen has been developed by scientists at the University of Western Australia. This regimen calls for normal diet and light training until the day before the race with a very short, very intense workout and 12g of carbohydrtae per kilogram of lean mass for 24 hours.

So how do the two factors of Alternate Day Fasting and a very low-carb diet affect the need for carb loading? For starters, I’m not sure what level of carbohydrate intake the submitter is referring to, but “ketogenic” makes me think we’re probably looking at 10% of calories from carbs, give or take. Now, the Alternate Day Fast is probably going to cause a depletion in liver glycogen just from general bodily functions throughout the day. But the muscles should stay relatively well-fueled since the glycogen stored in the muscles is only available to the muscles.

Activity level has a big impact on how often you need to “carb up”. Someone hammering away at the CrossFit Workout of the Day everyday has a higher need for carbs than someone following a standard split-routine of “3 sets, 8-12 reps, chest and triceps”. A sprinter has a higher need for carbs than a distance runner, contrary to what conventional wisdom would have you believe. As a rule, the higher the intensity of the effort, the more you’re tapping into muscle glycogen for fuel rather than fat.

The length of time between your glycogen-intensive workouts is also going to play a role. If you have an intense workout everyday, aside from likely living your life on the border on overtraining, you’re probably going to need to eat a good bit of carbs everyday, which makes the ketogenic aspect difficult to achieve. If you’re on a more reasonable training schedule, you’re probably hitting very intense workouts a couple times a week with days of pure strength work and days of pure skill work. For this type of schedule, I’d look at adding in the carbs after the intense sessions to maximize storage, along with some protein, and then count on carb intake on the days in between intense sessions to top up the reserves.

As in the discussion of portion sizes, the answer is “it depends.” You have to look at the types of activity you engage in, their intensity levels, and their frequency. Further, I’m betting that the fewer carbs you eat on a daily basis, the higher your need for carb loading to keep yourself fueled. And I’m sure this goes without saying, but I’m going to say it anyway. You need to eat high-quality foods as much as possible. Sweet potatoes, squashes, and fruits are better for upping your carb intake than resorting to grains of various sorts. Just remember that fructose is shuttled through the liver first, so isn’t great for refilling muscle glycogen.

Finally, just for fun, let’s look at just how much glycogen the body can store. The liver will hold about 100g, give or take. The muscles then hold another 200-400g, depending on your muscularity. So you’re looking at an average of, say, 1500 calories of fuel stored in the form of glycogen. With an effective carb load, you can increase that to perhaps 2500 calories of stored glycogen. Running and cycling burn glycogen at a rate of 600-800 calories per hour.(2) Looking at that, just how much need to you have for carbing up? I’m going to say that unless you’re doing extreme distances or training at a very high level, you probably don’t need to.

As I said, I am not one to intentionally carb load, so this is probably not the answer you were looking for. My daily carb intake is around 100g, after counting out fiber, totaling about 15% of my calories. Given my brief look at it, I now turn it over to you guys to discuss and hash about. Does anyone else have any other ideas or insights?

(1) Carbohydrate loading
(2) Bonk

Answers (1)
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Thanks for the post. I learned a lot about how my body uses and stores glycogen that I never realized.
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