Just a short plug for an interesting article. Mosaic Science, on January 26, published "Why the Calorie is Broken," and proceeded to discuss at length the means by which scientists arrive at caloric estimates for foods, as well as estimates of individual caloric requirements, and all the ways in which these can be inaccurate or variable. Some highlights:
- I know I was taught that food calories were determined by setting portions of food afire, then determining the amount of heat produced. However, scientists eventually recognized that we do not receive 100% available energy from foods, but leave portions of them undigested. SOOO... nowadays the scientists also burn people's poop after eating the foods, burn that, and subtract the two numbers. At least, I think I am understanding this correctly, though it is explained more delicately in the article, natch.
- The available calories in any given food, as opposed to those that remain indigestible, are radically altered by cooking the food. Raw foods have far less available calories than cooked foods, and the more cooked the food is, the more calories we will derive from it. A rare steak will be far less fattening than a well-done steak. Cooked carrots are a better energy source than raw carrots. But food calorie databases do not (and probably realistically cannot) reflect these differences. Processed foods are in many ways the most "cooked" of all, and may therefore have a greater energy impact than official calorie counts suggest.
- The commonly accepted idea that "genetics" significantly affects weight does not account for the growing obesity problem, which has developed in a time frame far too short to be much determined by genetics. Much more variation can be accounted for by individual differences in gut bacteria, which is more a question of internal ecology than of genetics. This ecology can be radically altered by, say, fecal transplants. Yes, eww, but they work. Or eating kimchi.
- "All of these factors introduce a disturbingly large margin of error for an individual who is trying...to count calories. The discrepancies between the number on the label and the calories that are actually available in our food, combined with individual variations in how we metabolise that food, can add up to much more than the 200 calories a day that nutritionists often advise cutting in order to lose weight. [...] None of this means that the calorie is a useless concept. Inaccurate as they are, calorie counts remain a helpful guide to relative energy values: standing burns more calories than sitting; cookies contain more calories than spinach. But the calorie is broken in many ways, and there’s a strong case to be made for moving our food accounting system away from that one particular number. It’s time to take a more holistic look at what we eat."