Calories vs. Fat grams

[ConstantChange]

Can someone explain to me how these effect the body different? When your working out I hear people say you burn so many calories doing such and such. How many Calories does a gram of fat have? Is it more important to eat something low in fat with higher calories or something that has slighty more fat but lower calories? I'm just really confused on the difference between the two.

 

[evenlu]

1 g protein = 4 kcal
1 g carbo = 4 kcal
1 g fat = 9 kcal
roughly

That's why it is so easy to become fat.