Why is carbohydrate muscle-sparing?
October 18, 2005 1:18 PM   Subscribe

What is the mechanism that triggers the breakdown of lean muscle mass for energy?

My admittedly vague understanding is that a condition of low blood sugar caused by a lack of carbohydrate intake, induces the breakdown of muscle tissue to keep the brain supplied with glucose. However, I'm simply overwhelmed by the mass of misinformarketing that comes up with every attempt to google out a clear explanation of this.

I'm looking for a reasonably simple and clear explanation of this process for the purpose of guiding an athletic diet. I'm wondering about things like why breakdown of fat can't supply the necessary glucose, how much carbohydrate must be consumed to avoid this state, etc.
posted by Manjusri to Health & Fitness (3 answers total)
 
'Ketosis" might be a useful word to google for.
posted by squidlarkin at 1:27 PM on October 18, 2005


Best answer: My admittedly vague understanding is that a condition of low blood sugar caused by a lack of carbohydrate intake, induces the breakdown of muscle tissue to keep the brain supplied with glucose.

This is true only if you're not eating enough protein. If you are, that'll be used instead. (Google "gluconeogenesis.")

I'm wondering about things like why breakdown of fat can't supply the necessary glucose

Because breaking down fat doesn't produce glucose, it produces ketones. Most parts of the body can burn ketones for fuel as well as glucose.

how much carbohydrate must be consumed to avoid this state

This varies widely, but most Atkins dieters find they can eat only 10-30 g of carbohydrates per day before they leave ketosis (i.e. the state in which you are burning ketones rather than glucose for most of your caloric needs). So, if you're trying to avoid ketosis, this is the minimum. If you are working out, the minimum will be higher -- certain muscle fibers are among the body tissues that require glucose.
posted by kindall at 2:28 PM on October 18, 2005


'Ketosis" might be a useful word to google for.

Sure, if you're interested in all that misinformarketing.
posted by rxrfrx at 2:56 PM on October 18, 2005


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