does your body still absorb vitamins and calories from the food you eat if you have diarrhea?

Answer 1

Technically speaking, yes. With diarrhea your intestines still generally have normal absorptive function (w/ certain exceptions relating to certain types of infectious diarrhea etc.) The problem simply is there's both too great a volume of material in the system and, more importantly, it passes through the intestines too fast. The end result is while you do absorb some calories and vitamins, you don't absorb nearly as much as usual.

All that said, this is rarely a concern with diarrhea. The danger lies not with inescapable starvation or vitamin deficiency, but with dehydration and electrolyte imbalances. Like when your body is starved of food and water because you're adrift in a boat, your greatest concern is not the lack of food but the lack of water. So it is with diarrhea where you get enough food and liquids in you but simply cannot do much with them.

Answer 2

No, it really doesn't. And what's even worse is that diarrhea depletes your body's stored nutrients, and may cause you to be dehydrated as well.