According to the Mayo Clinic, it takes an average of 53 hours to digest food completely. This is the amount of time that elapses between eating the food and excreting waste material through the anus.
The amount of time that digestion takes depends on a range of factors, including a person's diet, hormones and physiology, according to an article published in the Huffington Post. The Mayo Clinic notes that digestion times for children are usually shorter than those for adults, with the average being just 33 hours. HowStuffWorks explains that some parts of the donut, such as the sugar, are absorbed more quickly because these parts of the food are very easy to break down.