I like to think to present the appearance of being a human the Institute had to synthetically grow biological tissue in some cases, which needs to be fed in some manner.

Though being so little I don't think you'd have an amazingly high caloric demand and can go on for a bit without needing a bite. Sort of like Robo-Cop's diet.

[img]http://images.iherb.com/l/HTM-56004-1.jpg[/img]