Cells convert carbohydrate, fat and protein into ATP — the molecule that powers muscle contraction, nerve signals and nearly everything else.
How it works, step by step
Glucose is split in the cell fluid (glycolysis), making a little ATP.
Fragments enter mitochondria (citric acid cycle).
B vitamins act as coenzymes that carry electrons.
The electron transport chain uses oxygen to make most of the ATP.
Calories
A kilocalorie measures energy. Fat provides about 9 kcal per gram; protein and carbohydrate about 4; alcohol about 7.
B vitamins
Thiamin, riboflavin, niacin, pantothenic acid and biotin are all built into the machinery that releases energy from food.
Evidence & sources
Fat provides about 9 kcal per gram; protein and carbohydrate about 4 kcal per gram. Evidence: established. Known: The Atwater general factors used for food labeling. Unknown: Actual energy absorbed varies by food (e.g., whole nuts deliver less). Source: USDA / FDA, Atwater system — nutrition labeling (Current).