When does the body begin absorbing food calories?

your body burns calories it already has in it's system to process the food, but only a minor amount for most foods, protein and fibre takes more energy to process, regular sugar carbs break down the fastest, the most proteins, fat is usually the slowest. in general your body will probably start using the calories you just ate anywhere from 10-15 minutes after ingestion, and may continue to use them until they're finished in the large intestine