One of the reasons we eat food is to gain energy. how can we calculate the amount of energy that a food contains?

By calculating the total calorific value of each food ingredients

Explanation:

Food’s energy content is due to its calorific values or the amount of calories it it. Carbohydrate, protein and fat are the major constituents of a food. Suppose, the amount of carbohydrate, protein and fat intake in an adult is  equal to X, Y and Z grams  

In one gram of carbohydrate , protein and fat there are 4 , 4 and 9 calories per gram  

Thus, the total calories in the food of adult will be equal to  

calories

protein makes up the building blocks of organs, muscles, skin, hormones and pretty much everything that matters in your body.

some choices are:

peanut butter

seeds

eggs

yogurt

meats

fish

so pretty much meat, dairy, nuts, and grains.