Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
20 Oct

Dear Mark: Glycogen

Dear Mark,

I’m trying to understand how glucose that’s created by proteins and fats is used and stored. Is that ~200g of glycogen stored in the muscles to be used for exercise, or is it stored in the liver and used to fuel the brain and “day-to-day” functions? Also, if muscle glycogen is depleted, will ingested carbohydrates be used first to replenish muscle glycogen and then to fuel other daily functions, or are they used the other way around? I’d like to be able to use ketones to fuel my daily activity, but still have enough muscle glycogen stores to fuel intense exercise.

I always appreciate comments and questions that spur more explanation and discussion about the body’s functioning. Let’s take this one apart and have a look. Fat is always the best fuel to use at low levels of effort. We evolved to be very efficient fat-burners and even those of us at single-digit body fat levels have plenty to spare. Glycogen, as you remember, is stored glucose and is the body’s first-line energy stockpile of fuel for harder physical efforts and keeping specific systems (brain, red blood cells, kidney cells) running efficiently all day. It’s stored primarily in the liver and muscles; however, (of the two) only the glycogen stores of the liver can be used by the rest of the body. The muscles can’t share their stores. Selfish, you might say, but that’s how it works. As you suspect, the glycogen stored in the muscles (provided you aren’t taking in other glucose) is used along with fats to fuel physical activity throughout the day like your work out, your daily walk to the train, walk to the fridge, etc. The glycogen in the liver, while it can contribute circulating glucose to working muscles, generally serves up energy (reconverted glucose) to other parts of the body – the brain for example – as it sees fit.

As to the question of whether ingested carbs will go first to the muscles or to other functioning, it depends on lifestyle and how much you rely on carbs. If you are training hard every day and depending on a high-carb diet, the muscles will probably do a better job of storing those first incoming carbs from a meal eaten right after the workout. On the other hand, in the case of a low-carb strategy, the 200 grams a day you refer to are made in the liver via gluconeogenesis and mostly stored there to provide energy for vital functions. Yes, some will go to muscles recovering from a Primal-style brief-but-intense effort, but the rest stays in the liver and provides glycogen/glucose for the brain and red blood cells, etc.

Ultimately, though, this line caught my eye the most: I’d like to be able to use ketones to fuel my daily activity, but still have enough muscle glycogen stores to fuel intense exercise. I’d suggest looking at this kind of goal from a different angle. You really can’t have it both ways. Because you can’t override your body organs’ pecking order, it becomes a choice of either doing a ketogenic diet, which puts all your systems on an alternative fuel burning plan, or doing a moderately low carb diet that provides just enough glucose for your brain’s needs and for intense exercise bouts of an hour or less (centerpieces of the Primal Blueprint). If you’re looking to lose weight (fat), the ketogenic diet will be the most dramatically and swiftly successful. If you’re happy with the weight or are OK with a more gradual move toward your “ideal” body composition, the moderate-low path may be the way to go.

Finally, if it’s a question of fueling longer aerobic workouts (long distance running, for example), I’d suggest what I’ve said in the past. Endurance athletes, while they don’t need to indulge in the worst of the traditional carb loading, will need to make compromises to the Primal style. If they are “classically trained” in doing long workouts at 75-90% VO2 max, their bodies will simply require more glucose (and, hence, muscle glycogen) to accomplish the feats asked of them. In that case, ketones can’t play much of a role. On the other hand, it is possible – over a long period of time – to redirect gene expression to favor fat and ketone metabolism even at higher workloads. But this requires that the training be done at much lower heart rates for longer periods of time. That becomes the only way to recommend endurance athletes adapt their training and diet regimens to maximize fat burning efficiency. Check out Primal Compromises for Athletes for more on that discussion.

As always, thanks for your questions and keep ‘em coming!

Bob.Fornal Flickr Photo (CC)

Further Reading:

The Definitive Guide to the Primal Eating Plan

What Happens to Your Body When… You CARB BINGE?

The Context of Calories – 200 Calories is 200 Calories. Right?

Dear Mark: Did Our Bodies Evolve to Run on Ketones?

The Entire Definitive Guide Series

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. I am not sure if “they” have ever figured out what causes cramping. “They” used to think it was electrolyte imbalance, but the latest theory is your muscles cramp because they are not used to doing a certain motion/load. It might be either, or hydration, or a combination of some/all. Regardless, your muscles cramp b/c they can’t do what you want them to do anymore!

    Try keeping with your diet, *maybe* hydrating a little more, ran at this “hard” pace a little more often (do you warm up properly before running hard?), and maybe even included some stretching, you would stop getting cramps, or at least reduce them. Remember – its all about finding what works for you, so experiment!

    Let us know how it goes!

    Ryan Denner wrote on February 12th, 2009
  2. Thanks Ryan. I will def try some/all of your advice. I do intend to continue the diet and hope that this effect is something that I can work through or figure out how to combat it. I know i don’t stretch ‘enough’ and probably could hydrate a little more than I do. It had never been a problem before so it never bothered me. But being on a different diet I guess can lead to different physiological experiences. I tend to do a good job of hydrating in preparation for an even and def during the event. Thanks again for all of you guys’ help and answers. I will def keep you posted on how things go.


    armand wrote on February 12th, 2009
  3. Great read, I always enjoy reading about the specific details of your posts Mark.

    Jeff wrote on November 12th, 2010
  4. Mark you are wrong about the last answer, poor man who asked the question probably felt hopeless after reading this. Don’t you know about the TKD (targeted ketogenic diet) which is basically carb-loading 25-50 grams a 1/2 hour prior to high intensity exercise. It doesn’t disrupt ketosis in most people. Also it actually improves performance as opposed to the Standard Keto Diet for high intensity athletes.

    Dan wrote on December 7th, 2013
  5. “If you’re looking to lose weight (fat), the ketogenic diet will be the most dramatically and swiftly successful.”

    Completely wrong. A keto diet shows no greater rate of fat loss than eating the same amount of calories and including carbs. Why do people still think this?!!

    Mark wrote on January 30th, 2014
    • Finally some truth!

      Kelly Harris wrote on May 13th, 2014

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