Obesity is a growing global health problem that has received increasing attention in recent years. It has been estimated that over 700 million people in the world are classified as obese. In the UK, the obese population has more than triple in the last 25 years. Obesity has been identified as an escalating global epidemic health problem and is found to be associated with many chronic diseases, including type 2 diabetes, cardiovascular diseases and cancer. Although there is well-publicised guidance on recommended daily calories intake, very seldom people will comply with such guideline as recording of calorie intake is time consuming and inaccurate, as methods for dietary and daily activity assessments mostly rely on questionnaires or self-reporting.