what is food?how is provide energy in our body?

any thing which when eaten that provide us body nutrients 

for example carbohydrate protein fat and oil, vitamins minerals water

when we eaten any thing in our mouth saliva enzyme work and destruction and breakage of food

in our  body produce calories 

60-70% calories take our brain 

30-40% calories take our body without brain 

some enzyme work  naturally and some taken food