You will not see references made to calorie-counting in my book or articles. The only time a calorie may be mentioned is when making a point. I earned a PhD in Dietetic Nutrition and the theory about calorie calculation has bothered me for more years than I want to mention. 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. This is a simplistic statement about nutrition based on perfect conditions. If only we were perfect.
I was taught a scientific theory on calorie calculation based on American chemist Wilbur Olin Atwater from the 19th century. The available energy in all foods was calculated 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 breaking it up into smaller molecules. Atwater was doing his best, but no food is average. Each food source we eat is digested or unable to be digested in its own way.
According to Rob Dunn, a biologist at North Carolina State University, 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, genetically modifying it, or barbecuing it 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.
Rachel N. Carmody working in research states: “Even if two people eat the same sweet potato or piece of meat cooked the same way, they will not get the same number of calories out of it.”