How are the calorific contents of food worked out? Is it accurate?

Question

I have just eaten some salmon parcels and the packet said 129 calories for the two and I was just left wondering..

Answer 1

They put the food in a machine that burns the energy in the food and measure how much energy comes of it, therefore giving you the number of calories(amount of energy) in the food. I believe it is very accurate.

Answer 2

It is actually determined in a bomb calorimeter. A small portion of the food is burned in a very high pressure atmosphere of oxygen. The amount of heat released is measured very carefully. The idea is that when you metabolize foods, the same amount of energy is released as when you physically burn the food. Because of the what we know about heat and energy and about chemistry, that is certainly true.

Answer 3

The machine that does it is called a calorimeter, and it is highly accurate , however.....not all calories are equal, the fact that even water has a calorific value sems to suprise some people, and you can alter the effect these calories are used in the body, in fact chilling a glass of water to a very low temperature means the body requires to use more energy to consume it, (about ten calorioes extra for a 330 ml glass of iced water) various other calorific foods act in different manner in the human body, and some cause blood sugars to rise rapidly after consumption, (refined sugar, glucose, mars bars,) the result is that the body reacts with, first, a "sugar rush", of energy, and then overcompensates, because it trips the insulin production switch, that then reduces blood sugar levels, this in turn causes a feeling of hunger that starts it all over again, hence some foods promote obesity) there is a reason why dieticians call it (sugar) "pure white and deadly" an expression  that was once used for drugs, other foods take a longer time, to raise blood sugar levels, and do not cause a sudden insulin drop, these seem to promote healthy eating habits, and resrtict hunger desire, all food tested can be found by looking up a "glycaemic index" the lower the level on this index the less problems it seems to cause for overeating as the feeling of being full lasts longer, also the really magic food ? "celery", it takes more calories to eat and digest it than it contains within it !!! "Bon appetit", as the French say

Answer 4

The bomb calorimeter is very accurate in terms of measuring caloric content, but corrections have to be made to relate it to human consumption.  Humans do not digest certain compounds that have caloric content, such as fiber.  If you eat All Bran cereal, or lots of salad, you get almost no dietary calories.  But if you dry and burn them, you get a lot of heat.  People measuring calories have to subtract off the indigestible calories when they report the dietary information on your food.