Jay Aitchsee wrote:And then there's this - What is a calorie, anyway?
Of course, we all know that we're talking about the energy available in foods. But there's the physical amount of energy and then there's the physiological amount of energy. Or, the amount of energy that can be obtained by burning and the amount of energy we as humans can extract metabolically. I'm not an expert, but I gather from a little Google work that the caloric values of foods we see on labels is based on the physical value of energy contained in the components, i.e., fats, carbs, protein, and alcohol, of a food modified by a coefficient of digestibility as determined by one Wilbur Olin Atwater in the 1800's. Apparently, Atwater determined these coefficients by studying the amount of food remaining in the feces of various animals after having been fed the food in question.
Further it seems, these coefficients of digestibility are essentially those used by the USDA in its 1973 publication, the Energy Value of Foods, which would appear to be the basis for all caloric labeling currently in use in the U.S. As I understand it, the food for which the caloric content is to be determined is first broken down into its components, again fats, carbs, protein, and alcohol, by mechanical and/or chemical means and the Atwater determinants are applied to the amounts of each component found. There is no attempt to determine the physiologic calorie content of the whole food.
Again I'm no expert and I certainly could be wrong, but in my quick trip through Google space, I did not find any reference to suggest that caloric labeling of food today has been modified in any way by studies in humans to determine the true physiological caloric content.
Interesting, I thought.
Energy Value of Foods; USDA, 1973 http://www.nal.usda.gov/fnic/foodcomp/D ... s/ah74.pdf
How do food manufacturers calculate the calorie count of packaged foods? http://www.scientificamerican.com/artic ... ufacturers
e-Notes, calorie, http://www.enotes.com/calorie-reference/calorie-177741
Good point Jay. And those Atwater coefficients, are they the same for everybody? Certainly not. There are many factors that would enter into those coefficients like age, sex, size, ethnicity, gut flora, state of health, time of day, etc.
When trying to answer the question of what should we eat to stay healthy? -- One should simply ask what did humans eat for the last 200,000 years before there were doctors, and the USDA, and mass media marketing telling people how to eat?