I grabbed a couple food packages and did the math. One apparently subtracted the fiber calories, and one apparently didn't. I'm too lazy to try to carry this experiment on any further, as I don't eat a lot of extremely high fiber packaged foods (I get most of my fiber from vegetables).
It does make me wonder if calorie counters (in books and online) consistantly do or do not subtract the fiber calories. While my curiosity is piqued, not enough to do anything about it. My philosophy is do the easiest thing that works.
One thing that I do want to clarify though, because it's an important distinction. If fiber calories have not been subtracted, subtracting them is not at all equivalent to trying to estimate the "net" calories of a food (the usable calories minus the calories required to digest it - the negative calorie effect that some diets claim some foods to have).
In a very real way these calories do not exist for humans, because we cannot access them (to be blunt, they pass through the system undigested -unchanged). The calories in fiber(cellulose) is "locked" in the plant. It's as if you swallowed a hollow metal ball filled with fat - it would pass undigested and there would be no use in counting the fat calories because your body has
no way to access it).
Maybe that was too blunt a description, if so, sorry (Dad was an ambulance driver and EMT, and with some of the conversations we had at the dinner table, I don't always know when I'm being too graphic).
I've heard the rumors that some portion fiber CAN be digested, but scientific research refutes that. We don't have the enzymes needed to digest it. On a diet of primarily cellulose (whether it came from wood or lettuce), a human would eventually starve to death (if he/she didn't die of a bowel obstruction first).
Outside of the laboratory setting, the distinction really isn't important (unless you're one of those anal types who always has to be dead accurate even when it doesn't matter to anyone but you), because whether you're trying to gain, lose, or maintain your weight, you will adjust your calorie intake depending on what the scale "says." So as long as the numbers are moving in the right direction, your estimations are good enough.
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