- Food is energy for the body. Digestive enzymes in the mouth, stomach and
intestines break up complex food molecules into simpler structures,
such as sugars and amino acids that travel through the bloodstream to
all our tissues. Our cells use the energy stored in the chemical bonds
of these simpler molecules to carry on business as usual. We calculate
the available energy in all foods with a unit known as the food calorie,
or kilocalorie—the amount of energy required to heat one kilogram of water
by one degree Celsius. Fats provide approximately nine calories per
gram, whereas carbohydrates and proteins deliver just four. Fiber offers
a piddling two calories because enzymes in the human digestive tract
have great difficulty chopping it up into smaller molecules.
Every calorie count on every food label you have ever seen is based on these estimates or on modest derivations thereof. Yet these approximations assume that the 19th-century laboratory experiments on which they are based accurately reflect how much energy different people with different bodies derive from many different kinds of food. New research has revealed that this assumption is, at best, far too simplistic. To accurately calculate the total calories that someone gets out of a given food, you would have to take into account a dizzying array of factors, including whether that food has evolved to survive digestion; how boiling, baking, microwaving or flambéing a food changes its structure and chemistry; how much energy the body expends to break down different kinds of food; and the extent to which the billions of bacteria in the gut aid human digestion and, conversely, steal some calories for themselves.
Nutrition scientists are beginning to learn enough to hypothetically improve calorie labels, but digestion turns out to be such a fantastically complex and messy affair that we will probably never derive a formula for an infallible calorie count.
Thursday, 22 August 2013
Scientific American on Calorie Counting
We've been here before. Originally phrased in Paleo as "calories don't count", evolved in to "why count calories", and now reformulated as "can you count calories". Some of us don't count calories. Calories still count, but how effectively you can count them is the crux of the matter. Isocaloric is not isometabolic - as Scientific American report,