I've often wondered how we've come to the consensus of: carbohydrate = 4 kilocalories protein = 4 kilocalories fat = 9 kilocalories alcohol = 7 kilocalories I

I've often wondered how we've come to the consensus of: carbohydrate = 4 kilocalories protein = 4 kilocalories fat = 9 kilocalories alcohol = 7 kilocalories It seems difficult to quantify this accurately without fully understanding human metabolism and how it utilizes energy sources.