The weight has dropped off her dramatically and a source says she's over a half stone lighter in the past 4 weeks.
William has been very concerned and has urged her to eat all the time and she does try, but her stomach has shrunk and she's happier with the subsistence of juices and the occasional salad, vegetables and a piece of lean chicken or white fish, all steamed or grilled.
Her favorite purees are oranges, pineapples and banana purées. The source said a typical calorie count for one of Kate's day is often no more than 800 calories, and her advisers and even her wedding dress designer have become concerned because of how much she's losing on a daily basis.
Kate barely eats any solid food, said the source. She is drinking a lot of water and also warm water with lemon juice, and the solid food she is having is very light and she never eats much.
The source said her wedding dress has had to be taken in a few times over the course of the past 3 weeks.
Her cake maker, Fiona Cairns, has even joked with her that she's going to send her a few cakes before the wedding to build her up, said the insider, who also added that Fiona and a team of 7 are based at the Palace at the moment creating the cake, and in daily contact with Kate.