It's close enough to get results. Nobody is going to put a sandwich from the local sandwich shop into a bomb calorimeter to figure out how many sandwiches they can eat and still lose weight.
If you're going to get hung up on the term calories let's call them approximate calories (or ACs) instead. If I eat mostly the same foods all the time I can use reasonable guesses to get the ACs in each food. Foods I eat infrequently will probably have a greater deviation between my ACs and the actual calories but that doesn't matter much because I don't eat them very often. Foods I eat frequently will probably have less error and the error doesn't matter much as long as I'm consistent with the numbers.
Let's say I decide I want to lose weight. I can start off with the general rule that for a male of my age, build and activity levels I need about 2500 calories a day to maintain weight. Since I want to lose some weight I'll set my daily AC allowance at 2000. After a couple weeks I check how the weight loss is going. Am I losing weight too slowly? Drop the ACs a bit. Am I losing weight too quickly? Increase the ACs a bit. Keep checking and adjusting every couple weeks until I'm happy with the weight loss.
This approach works in the real world. I do weigh and measure some of my food but if I had to weigh everything down to the last gram to make sure I ate exactly 1947 calories per day for ideal weight loss I'd quit pretty quickly.
If you're going to get hung up on the term calories let's call them approximate calories (or ACs) instead. If I eat mostly the same foods all the time I can use reasonable guesses to get the ACs in each food. Foods I eat infrequently will probably have a greater deviation between my ACs and the actual calories but that doesn't matter much because I don't eat them very often. Foods I eat frequently will probably have less error and the error doesn't matter much as long as I'm consistent with the numbers.
Let's say I decide I want to lose weight. I can start off with the general rule that for a male of my age, build and activity levels I need about 2500 calories a day to maintain weight. Since I want to lose some weight I'll set my daily AC allowance at 2000. After a couple weeks I check how the weight loss is going. Am I losing weight too slowly? Drop the ACs a bit. Am I losing weight too quickly? Increase the ACs a bit. Keep checking and adjusting every couple weeks until I'm happy with the weight loss.
This approach works in the real world. I do weigh and measure some of my food but if I had to weigh everything down to the last gram to make sure I ate exactly 1947 calories per day for ideal weight loss I'd quit pretty quickly.