Why fats are reserve fuels? Why not Carbohydrates?

Consider an adult male of weight 70 kg. Fat produces 9 cal/g of
energy. So its enough for us if we have fats of about 15 to 20% of our
whole body weight. i.e. About 10 kg in adult male. Whereas
Carbohydrates normally produce 4 cal/g of energy. So more amount of
carbohydrates required to survive through same amount of days... i.e.
about 50 kg. so if carbohydrates would have been used as reserve of
energy the weight of normal adult male would have been 70-10+50=110
kg.
* The humming bird can fly 2400 km from england to west indies for 60
hr continuously because of stored fat...
*Bear hibernates for 7 months in an year and still survives because of
stored fats...



--
Shrinidhi L K
KIMS, Banglore