Hi Gemma. Cambridge diet is basically shakes and is a very low calorie diet. There are different levels to it but the most basic is 3 or 4 (shakes/porridge or bars) a day. It puts your body in a state called ketosis where you burn fat and aren't hungry. It is a fantastic diet if you can go without food (or very controlled foods). On my first week I lost 11lbs but I have seen someone lose 18lbs! It becomes harder as you work up the plans and start introducing food again as you have to count calories, thats why alot of people switch to SW or WW so they don't have to do the counting x