Very Low-Carb Trip Report

[John S.]

Hi Tom. Check out this linked article.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2958805/pdf/pcbi.1000960.pdf

The amount of glycogen storage depends on mass of liver and muscle. Trained athletes can apparently attain muscle glycogen levels upwards of 570 grams. Supposedly, Tim Noakes, MD's book says muscle glycogen can go up to 720 grams, but I have not found those studies proving that.

[Anonymous]

"Trained athletes can apparently attain muscle glycogen levels upwards of 570 grams."

John – The operative qualifier in the article is "trained" and, even for them, the typical amount of muscle glycogen is 300 grams according to the article. 570 grams is considered to be the maximum attainable after following a very rigorous, scientific approach to glycogen loading. This thread, AFAIK, addresses the capacity of normal people. Same goes for the liver, unless I have totally misread the article.

In another vein, thanks for posting the link. It is a darned interesting article in its own right, and I shall be reading it closely in its entirety in the near future for my further edification. I'll be interested to see if they get into the size and number of mitochondria in trained athletes, as well as their ability to derive more of their energy from fat due to said mitochondria and extremely high VO2 max, thereby delaying the onset of glycogen depletion. That, to me would offer an explaination of the ability of world class marathoners to kick it in at the end of a marathon which they have run at an ~4:40 min/mile pace for the first 25 miles or so.

[John S.]

No doubt those numbers in the article are "trained" athletes. The numbers for average persons are what seem to be quoted in medical biochemistry texts (about same numbers you had mentioned).

[Lynn Tramper]

You can pick and choose which articles to quote as to how much glycogen an 'average' male may store when rested and well fed, but even taking the lowest estimate of 300g carbohydrate stored, it just doesn't make sense to 'bonk' on a day hike unless something is pretty out of kilter. Unless you are exercising very intensely, you are almost never burning 100% glucose for fuel. At 50% VO2 Max you are probably burning around 50% CHO and 50% fat. So that means 1200 calories from (stored) carbs and 1200 calories from (stored) fat if you ate nothing during your hike. When carbs get low, your body will then move into gluconeogenesis, from fat, protein or both. Marathoners 'hit the wall' because gluconeogenesis and absorption of carbohydrates from food cannot keep up with the burn rate, but this doesn't seem to be greatly affected by duration, only distance (the famous 18 mile crunch). But they are usually running at greater than 50% VO2 Max, probably closer to 70%, thus burning a higher proportion of glucose compared to fats (around 70% carbs/30% fat). That is assuming you are not 'fat adapted' to exercise.

However, another thing to consider is that hiking uses mostly legs muscles, and neither glycogen nor intramuscular triglycerides can be shuttled from, say you arm muscles, to your leg muscles. Same with running. In any event, it is not 'normal' to run out of glycogen/glucose that quickly, and you certainly would not see things restored that quickly with a meal of only protein and fat if you had run out of glucose. Jack may have experienced a reactive hypoglycemic episode on his previous hike, but the rapid recovery in the absence of simple sugars points more towards gluconeogenesis (i.e. a rest) making the difference than the food he ate. If jack is a reactive hypoglycemic then there is no doubt that eating less carbs will probably help, both his hiking and long term health. As I've mentioned in other threads, I am a real big fan of knowing rather than guessing, so would be inclined to carry some blood glucose test strips and see what my glucose levels are really like if that happened again. It won't tell you what you insulin levels are, but if you are not shooting insulin and you become hypoglycemic, it's a pretty good indicator of insulin resistance (or exercising at a very high intensity or a prolonged period of time).

[Anonymous]

"You can pick and choose which articles to quote as to how much glycogen an 'average' male may store when rested and well fed,"

I'd be most interested in reading an article or two of your choosing that support 700-1000 grams of stored glycogen for the average 70 kg male. I've never heard of anything remotely in that range. Can you supply any supporting references? The authors of the article John Shannon referred to have figured out that it requires a little over 2900 calories for a 70 kg runner to complete a marathon. If that runner had 700-1000 grams of stored glycogen available, assuming the vast majority of it is in the leg muscles, there would be no question of "hitting the wall", especially considering that said runner would not be burning solely carbs.

"but even taking the lowest estimate of 300g carbohydrate stored, it just doesn't make sense to 'bonk' on a day hike unless something is pretty out of kilter."

Agreed, but Greg G's suggestion that he may have been low on glycogen to start with sounds a bit more likely than some underlying pathology. Hard to say without a lot more information than we have at our finger tips, not to mention we're not physicians.

[Lynn Tramper]

"'I'd be most interested in reading an article or two of your choosing that support 700-1000 grams of stored glycogen for the average 70 kg male."

I will do this when I have time and decent internet access. In the mean time, I think you will find that the articles you have been citing RE: ~300g glycogen in muscles, is in reference to marathon runners and is only talking about glycogen stored in leg muscles, which is why I worked with that lower number. It is based on a LOT of assumptions, such as being a young male (the OP is not) and that this mythical young male is almost half total muscle (45% actually), and that half that muscle is in the leg muscles, and assumes the muscles are fully glycogen loaded (not super-compensated) to start with. So the lower number of 700g total glycogen reflects ~300g in legs, ~300g in upper body, and ~100g in liver. A well trained athlete can reach over 1000g total. However, we are not talking about a marathon, which burns carbs at a higher rate than your average backpacking trip.

Now Jack is not young, I don't know his weight, and don't know how much of that weight is muscle. What I do know is that he has been following a low carb diet in general, and presumably on the day he 'bonked' he deviated from this low carb approach. Thing is, someone who has been eating low carb and then suddenly eats carbs should be very insulin sensitive, so all the carbs he eats should have gone to glycogen recompensation. Maybe he just didn't eat enough carbs to fully reload his muscles, yet the carbs he did eat meant he rapidly left fat-burning mode for glucose burning. This doesn't require any pathology, just not enough carbs and a loss of a fat-adapted physiology on the day. Or it may be that he really doesn't have enough leg muscle mass to sustain glucose-based exercise for any length of time. However, there are plenty of older people who do not appear to have a lot of muscle mass and they do just fine with mainly carbs. The trick being they replace the carbs with food as they go (as do most marathon runners). Jack didn't do this. But his quick recovery with a lack of carbs doesn't really indicate that low glycogen was the culprit. As mentioned before, it doesn't really matter as long as Jack finds a low carb trail approach suits him. Everything else is just academic.

[Laurie Ann March]

I use both carbs and protein on my trips. It works very well for me. Protein and fat will helps slow the rise of the carbohydrate so that you have energy over a longer period of time rather than the sudden burst and crash. Fibre helps too. I tend to use things like lentils and chickpeas because of their protein and carb combination and then make great additions to things like chili for dinner or as a no-cook salad at lunch. Keep in mind that there are some carbs in things like salami and certain cheeses albeit minute. Fat can also cause a surge of glucose into the blood stream (I've noticed it at home when I eat eggs) but that surge doesn't happen until hours later.

I've found that I can't rely on not having carbs. Because my muscles taking up glycogen for energy there is no really good way for me to predict it and there are just too many other factors.

Hey… if you really want to know how your body handles carbs… get a blood glucose meter (I'm serious here). It certainly tells you what's going on in that aspect.

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