Weight loss: calculate food energy

Not all of the energy in foods and alcohol is available to the body's cells. The processes of digestion and absorption are not completely efficient, and the nitrogenous portion of amino acids is not oxidized but is excreted in the form of urea. 

Therefore the biologically available energy from foods and alcohol is expressed in values rounded off slightly below those obtained using calorimeter.

Values:

• protein – 4 kcal/g, 
• fat 9 kcal/g, 
• carbohydrate 4 kcal/g, 
• alcohol 7 kcal/g. 

Although the energy value of each nutrient is known precisely, only a few foods (oils and sugars) are made up of a single nutrient. Foods contain a mixture of protein, fat and carbohydrate. 

1. Example: 

Energy value of one medium size egg (50g).

Protein: 13% x 50g = 6.5g x 4 kcal/g = 26 kcal

Fat: 12% x 50g = 6g x 9 kcal/g = 54 kcal

Carbohydrate: 1% x 50g = 0.05g x 4 kcal/g = 2 kcal

Total: 82 kcal 

   2.  Example: 

Energy value of alcoholic beverages and mixes.

The energy value of alcoholic beverages, which is expressed in kcal, can be determined by the following equation:

Kcal = amount of beverage (oz) x proof (the proportion of alcohol to water or other liquids in an alcohol beverage. The standard n the US defines 100-proof as being equel to 50% of ethyl alcohol by volume) x 0.8 kcal/proof/1oz (factor that accounts for the caloric density of alcohol and the fact that not all of the alcohol in liqour is available for energy).

To determine the percentage of ethyl alcohol in a beverage, divide the proof value by 2 (86-proof whiskey contains 43% ethyl alcohol).

The number of kcal in 1 ½ oz of 86-proof whiskey would be determined as follows:

1 ½ oz x 86-proof x 0.8 kcal/proof/1 oz = 103 kcal