A calorie is a unit of energy. In nutrition and everyday language, calorie refer to consumption through eating and drinking and energy uses through physical activity.
There are two types of calorie ( only for clarity) --
1. Small calorie ( symbol- cal , 'c small',)-- 1 cal. is the amount of energy or heat required to raise one gram of water by one degree Celsius.
2. Large calorie ( symbol- Kcal ) -- one calorie is the amount of energy or heat required to raise one kilogram of water by one degree Celsius.
1 Kcal = 1000 calories
Most people associate calories just with food and drink, but any thing that contains energy has calories.
Nowadays on food packages there are sometimes mentioned two measurements of energy, Kjoules or Kj and Kcal . Kilojoules are alternative energy measurement mostly used by scientific community. One Kcal is equivalent to 4.2 Kjoules.
Normally Kcal is referred to simply as calorie.
Most of the calories in food comes from three macronutrients-
1. Carbohtdrates have 4 calories/ gram
2. Protein has also. 4 calories/ gram
3. Fat. has. 9 calories/gram
So, one can make adjustments in food to get required calories and also how much calories one wants from each macronutrients.
A few words about alcohol, it doesn't contain any fat ,yet one gram of alcohol contains 7 calories. Please also remember, non alcoholic beer has also same amount of calories. An average pint contains 190 calories.
So the question is how much calories an average adult requires ? The requirement depends on several factors including overall health, physical activity, sex, height and weight etc.
There are certain recommendations ---
Men. Women
U.S. 2700 calories. 2200 calories
NHS, UK. 2500 calories. 2000 calories
FAO, UN. say an average adult should not eat less than 1800 calories.
nutracheck.co.uk/ library/calories/understandingcalories_1html