Many celiacs lose weight before they are diagnosed; indeed it is often one of the reasons people go to their doctors in the first place.
Once on a gluten-free diet the symptoms disappear, and as a result of better absorption or simply eating more, some people gain too much weight.
Losing weight should be based on eating sensibly rather than lurching from one diet to another. Be wary of low carbohydrate diets, as high protein diets can cause acidosis, which in turn can lead to calcium being lost from the bones.
You should always check the ingredients of any low calorie / low fat / low carbohydrate products as they may use ingredients containing gluten to thicken or stabilize the product. These are often wheat based.
Moderation is the key. Don