Women are supposed to have about 2000 calories a day and at the moment, most of us are existing on under 500 - so even with a few prawns (so long as they are not in batter!!!) the calorie intake is still exceptionally low and cant do much harm. They may be salty but isn't that just about fluid retention as opposed to fat?
I'm not advocating deviation I just don't think we should get twisted out of shape over 'expanding' the menu from time to time - calorie intake is still well below and carb intake almost non existant.