Although obesity surgery is currently the most effective method for achieving weight loss, not all patients lose the desired amount of weight and some show weight regain. Previous pilot work by the lead researcher shows that successful weight loss is associated with the amount of investment the patient feels that they have made in their operation. For example, those who feel that it has taken more time and effort to organise, has cost more money, has been more disruptive to their family, social and work lives and has caused pain are more likely to lose weight after their operation. Therefore, it seems as if the greater the sense of investment, the greater the motivation to make the operation a success. The present study aims to build on these findings by encouraging weight loss surgery patients to focus on the investment they have made, thus making their investment more salient to them. Using a trial design, half the patients will be asked to rate and describe the investment they have made in their operation just before surgery (focusing on the time and effort to organise the surgery etc) and 3 months after surgery (focusing on time off work for recovery, disruption of family and friends, pain of surgery, pain of having the stitches removed etc). All patients will record their weight, beliefs about food, intentions to change their behaviour and actual eating and exercise behaviour at baseline then 3, 6 and 12 months follow up. The impact of the investment based intervention will then be assessed to explore whether focusing on the investment involved in having surgery improves patient health outcomes by one year.