This isn't so. Quoting [1], energy dissipated as side-effect heat during gestation and storage:
Carbohydrates: 5 to 15% of the energy consumed
Protein: 20 to 35%
Fats: at most 5 to 15%
Carbohydrates: 5 to 15% of the energy consumed
Protein: 20 to 35%
Fats: at most 5 to 15%
Doesn't this assume that you're starving [1]? Proteins are a last resort, and since it's somewhat toxic to convert them, they're simply not processed if it can be avoided [2].
[1] https://en.wikipedia.org/wiki/Gluconeogenesis "the process occurs during periods of fasting, starvation, low-carbohydrate diets, or intense exercise."
[2] http://antranik.org/the-catabolism-of-fats-and-proteins-for-...
Not only is the fat digestion process inefficient, but on top the fat absorbtion process consumes more energy to make happen ( that heat )
We'd have to see where in the large 5-15% ranges various items stand.
Sugar dissolving in water... I'd be amazed if that released 15% of the energy. I'm still amazed it would be as high as 5%, so thanks for that info
EDIT: spatular set me straight with a detailed process for sugar absorbtion
I think longer hydrocarbons including sugar have to be broken into fructose and glucose during digestion. Fructose cannot be immidiately consumed by cells, so it's converted into glucose in liver. On top of that, there are about 5g of glucose total in bloodstream at any given moment, so exess have to be accumulated by liver/muscle cells that have to store it in a long-chain hydrocarbon form (glycogen). Each conversion requires some energy, so 5-15% isn't that much...