Published: 23:19 GMT, 19 August 2013 | Updated: 23:34 GMT, 19 August 2013
Some people will always be punctual, while others are perpetually late — and our bodies are no different.
A recent study by the U.S. National Institute of Environmental Health Sciences found that ‘due dates’ are largely pointless, because the length of pregnancy can vary dramatically from woman to woman, with very few actually giving birth on their predicted day.
So what about the other crucial processes in life — how long should they last? CHLOE LAMBERT and ROGER DOBSON asked the experts.
DIGESTION: 24 hours
That sausage roll you’ve just scoffed will be in your stomach within three seconds of swallowing it, but the waste won’t be excreted until up to a day later.
Complex: High fat foods can hours for the stomach to break down
As soon as it reaches the stomach, it’s ground into tiny particles with the help of stomach acid, at a rate of about three to four calories a minute, says Dr Anton Emmanuel, consultant gastroenterologist at University College Hospital, London.
‘A larger meal with a high fat content will be harder
for the acid to break down, but a 600-calorie roast dinner, for instance, will be in your stomach for about two to three hours.’
Next, the food travels through the small intestine where it’s further broken down, and nutrients absorbed into the bloodstream, before entering the colon after another two to three hours, where water and salt are extracted.
‘For the next 20-odd hours, it’s working its way through your colon so the whole thing takes about 24 hours,’ says Dr Emmanuel.
‘But there’s a huge variation in what normal is — anything from 16 to 30 hours for a standard meal is considered healthy.’
Individual foods vary in time taken to pass through. A study from the University of Hawaii found it takes up to three days to digest a complex food such as a hamburger, whereas fruit can take less than an hour.
Digestion is a bit slower in women than men — possibly because the gut hormones that aid digestion are less powerful in women, says Dr Emmanuel.
Digestion also slows down with age as the system becomes less effective; drugs such as blood pressure medications and antidepressants can cause the bowel to slow right down.