Can not eating enough fat cause constipation and fluid retention?

Not really: Though you should look at your diet. Foods which cause constipation are usually the grains:rice, barley, oats; milk; bananas. Lay off of those in your diet for a week and your constipation will probably resolve. As to the fluid retention at 22 you probably don't have kidney disease but you may be on BCPs. These are steroids and as a side effect can cause fluid retention. Talk to your doc about ano