點解脂肪既能量多過碳水化合物?

圖片參考：http://content.answers.com/main/content/wp/en-commons/thumb/9/93/200px-Glucose-2D-skeletal.png

Glucose C6H12O6 or C6(H2O)6
Molar mass for C is 12g and H2O is 18g.
It may be due to the fact that 60% of mass of carbohydrate is H2O which will not contribute any energy output in combustion, only the other 40% of mass is carbon to contribute energy output in combustion.
Energy rating for carbohydrate(碳水化合物) is about 4 calories per gram, while fat(脂肪) is about 9 calories per gram.
I hope this can help your understanding. :)

因為脂肪＝肥，碳水化合物＝健康