Why does the body use up carbohydrates before lipids?
because lipids act as an energy store so only when there is little supply of carbohydrates will the body respire lipids. Vertebrate muscles is likely to respire fatty acid as glucose.
I am not exactly sure how to answer a why??? The only answer would be a philisophical one. That is our primary source of energy. Fat is used for storage, insulation and protect. Like mentioned above when carb stores are low, then energy will be obtained from muscle and fat cells.
Carbs are more simple molecules. They can be broken down into glucose much quicker by the enzyme glucagon (i think that's the one) and so are more readily avaliable when & where nessecary.
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