In this study, we consider body composition measurement together with an immediate brief counselling after the measurement as part of the intervention. The body composition measurement will allow the participants to get familiar with their own anthropometric data and serve as cues to actions of healthy diet adoption and weight management and control. Based on the measured body fat and anthropometric data, a trained research assistant will give brief individualized dietary and weight management counselling to the participants.

The Whatsapp-based counselling and communication will heighten the awareness through reinforcing the need and benefits of body composition and weight control, the importance of energy balance, as well as providing professional and tailor-made advice on healthy eating and weight management. Qualitative dietary counselling will be offered every two weeks through the Whatsapp.

Participants in the control group will receive the simple body composition measurement only, without an immediate counselling after the measurement. Whey will be informed the values of anthropometric data and body composition parameters, no detailed interpretation of the values will be delivered to them. They will also not receive the professional consultant of the healthy diet and weight management from the diatetitian during the intervention period.

As for the body composition assessment, body fat and muscle thickness, body fat percentage and distribution will be measured and a brief face-to-face counseling soon after the measurement will be implemented to the participants. Body assessment were measured by the InBody 270 (Biospace, Seoul, Korea) device, which provides a convenient way of accurate body fat measurement comparable with those obtained using air displacement plethysmography (ADP) (about 90% precision).

As for the Whatsapp-based counselling and communication session, qualitative dietary counselling will be offered every two weeks through the Whatsapp. One session contains 15 minutes, including the topics like making a balanced diet (55 % glucose, 30 % lipids and 15 % proteins), diversifying food intake, dietary advices and recommendations in healthy eating behaviors (e.g., eat slowly, eat at a regular time, avoid to skip a meal, drink at least 1.5 L of water each day).

Four items from belief domain of Chinese weight management scales (WMS) was used to measure the participants' belief of self weight management . Each item is measured by 3- or 4-point Likert scale. The total score change from 4 to 15 with higher scores indicating better weight management belief.

The knowledge of weight management was measured by 13 items from the general nutrition knowledge questionnaire (GNKQ). Each item carries one point for a correct answer and the maximum score is 13. A higher score shows better weight management knowledge.

Respondents' food knowledge and behavior were obtained through the food behavior questionnaire (FBQ). The FBQ is a questionnaire with 18 questions querying respondents' behaviors and knowledge about various areas of food and diet-related health such as nutrition label reading behaviors, knowledge of diet/disease relationships and some meal consumption patterns.