It seems that part of the more recent trend of defining a "proper" low carb diet as being one that is moderate in protein and high (very) in fat is this notion that excess protein will just be turned to glucose. Quite often I've seen Dr. Richard Bernstein cautions against eating too much protein because it just gets turned to glucose. (I did look for a link but was unsuccessful, so if I'm misstating Bernstein here, please do correct me in comments.) I had looked into this long ago, but never really said much about it, but there are two reasons why this never made sense to me.
First, a little biochemistry. There are exceedingly few reactions that occur in our bodies without the involvement of an enzyme. This includes not only anabolic (synthesis, building, energy storing/requiring) reactions, but also catabolic (break down, energy releasing reactions) reactions. Glucose and fatty acids no more "spontaneously combust" in our bodies than does propane in my grill. Enzymes are the catalysts of reactions, and reactions that require energy (all of those "genesis" reactions for example) are coupled with energy producing reactions that "drive" them. Enzyme action is regulated by the amount of the enzyme produced and/or some mechanism of activating/deactivating the enzyme. While enzyme mediated reactions can be related to substrate (reactant) availability and/or influenced by product availability/build-up, this isn't always the case. I'd even go so far as to say that unless the reaction occurs in a highly compartmentalized fashion (e.g. within mitochondria), substrate/product concentrations generally have little effect on the reaction rates directly.
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First, a little biochemistry. There are exceedingly few reactions that occur in our bodies without the involvement of an enzyme. This includes not only anabolic (synthesis, building, energy storing/requiring) reactions, but also catabolic (break down, energy releasing reactions) reactions. Glucose and fatty acids no more "spontaneously combust" in our bodies than does propane in my grill. Enzymes are the catalysts of reactions, and reactions that require energy (all of those "genesis" reactions for example) are coupled with energy producing reactions that "drive" them. Enzyme action is regulated by the amount of the enzyme produced and/or some mechanism of activating/deactivating the enzyme. While enzyme mediated reactions can be related to substrate (reactant) availability and/or influenced by product availability/build-up, this isn't always the case. I'd even go so far as to say that unless the reaction occurs in a highly compartmentalized fashion (e.g. within mitochondria), substrate/product concentrations generally have little effect on the reaction rates directly.
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