Though I've been doing well on Slimming World and actually enjoying the food I'm eating, I was only going to the toilet once a week at the most. I was eating loads of fruit and veg, having All-bran every morning, drinking 3 litres of water every day, but no change.
I started doing some research and, like you, found that this was most likely due to the lack of fat in my diet. I didn't want to go off plan so instead I have a teaspoon of cold pressed organic virgin coconut oil (2 syns) every day. It's not as bad as it sounds, honest. It does start off with a lard like consistency but it melts within a second or 2 in your mouth and has a pleasant coconut taste. I also use it for cooking instead of the spray oils, it works great in the actifry, my sweet potato and butternut squash chips were lush.
Coconut oil contains good fats that are actually supposed to help with weight loss, especially losing the fat around your organs. It's also really good for digestion and, since starting it just over a week ago, I've been going to the toilet every second day, so a massive improvement. A BIG relief, let me tell you.
I've also started using the coconut oil as a body moisturiser and hair conditioning treatment, it works fantastically well.