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How Much Water is Released by Glycogen 'Burning'?
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The use of glycogen by muscles for energy (“‘burning” glycogen) releases quite a bit of water. Fat burning does also, to a lesser extent.
It is one reason that going into a hard ride with full muscle glycogen stores can delay dehydration, and why calculated fluid-intake needs are at variance with actual dehydration effects, an effect repeatedly observed and documented by your author on 3-4 hour rides: the weight vs hydration variance was puzzling.
The effect is very significant. For example on 6 ascents of Old La Honda, I consumed 184 grams of Hammer gel, but with the hard efforts, my muscles probably burned off at least 200 grams (800 calories) which would have released 3 X 200 = 600 grams of water, or 1.3 pounds (1.3 pints) of water!
According to UltraCycling.com:
- Each gram of glycogen is stored with 3 grams of water, so filling glycogen stores with an additional 300-500 grams should lead to a weight gain of up to 2 kg. Don't worry—most of this additional weight is water, and will actually be helpful during the ride.
- Glycogen supercompensation, or carbohydrate loading, helps prolong endurance in events lasting over two hours. Estimates are that it can move the wall about 20% farther down the road.
- Taper your training during the week before the event, ending with either a rest day or an easy spin. This will allow dietary carbohydrate to be stored as muscle glycogen rather than being used as a fuel for cycling.
- In conjunction with backing off the mileage, you need to increase carbohydrate intake for the last 3-4 days of the week—aim for 8-10 grams of carbohydrate per kilogram body weight.
I (Lloyd) rely on this and have to compensate for this water-release with glycogen burning for double centuries. See also Nutrition for a Double Century.
Matthew C writes:
This is definitely true. It's also the reason we rapidly lose weight in the first few week or so when dieting, and especially when doing a low-carb diet.
After the initial depletion of glycogen stores (and hence water) the weight loss tapers off to a pound or so per week. Glycogen stores are rapidly depleted, along with water.
WIND: makes sense. A neat trick used by companies selling immediate results on diet plans—no real gains, but feels good.