Few things are as irresistible as slumber's post-lunch siren call, but why do we feel sleepy after eating? After all, food is an energy source, not an energy sapper — right?

Unfortunately, the human body isn't that simple, with a cornucopia of factors coming into play to determine how tired a person feels.

"When we eat a meal, it spurs a series of actions in the gut and across the body," Claire Shortt, a nutritionist with a background in microbiology, told Live Science.