hi there Alisonia

Its one of those "your mileage may vary things" Strictly speaking diet drinks are ok on a LC diet...from a carb point of view.

Trouble is some people react strangely to the artificial sweetners in them and they can cause stalls and water retention.

The kilo you seemed to gain back could be water retention from the diet coke or it could just be a natural fluctution. It is impossible to have gained 1kg of fat overnight..so don't panic

You may need to experiment a little more to be certain.

For me I can't have too much as it gives me raging headache.....but that's a whole other story

Lesley