Thyroid hormones play an important role in the regulation of the body's metabolism. But the relationship between thyroid hormone status and the basal metabolism rate is not absolute. Because thyroid hormone function is not the only factor of control the metabolism and it can be influenced by various factors such as physical activity and diet.

Weight change after thyroidectomy is one of the concerns for thyroid cancer patients. The evidence on the bodyweight changes following thyroidectomy has not been established well. Being overweight and obese can increase the risk of developing many potential health problems, such as heart disease, diabetes, high blood pressure, and malignant disease.

Recently, digital health care technology has been developed and applied for medical purposes in many clinical practices. Digital Lifestyle Management is one of the strategies that can be helpful for the obese to control their body weight by lifestyle modification. It provides comprehensive, multifactorial, intensive interventions which are delivered via the digital health care mobile service Noom application.

The aim of this study is to evaluate the efficacy of digital lifestyle management on body weight and quality of life after total thyroidectomy in thyroid cancer patients by using the digital health care Noom application.

The present study is a prospective randomized control trial. A total of 80 patients who underwent total thyroidectomy for thyroid cancer is included. Fifty-four patients are randomly assigned to the digital lifestyle management group and the other 26 patients are assigned to the non-digital lifestyle management group.

In the experimental group (digital lifestyle management group), the patients will use this application for the first 4 months with Noom applications with 1:1 personalized coaching intervention, and then, use this app by self-help program without coaching intervention. The digital lifestyle management program will record the patient's meals, exercise, steps taken, reading articles, and give feedback to each patient. In order to monitor the psychological state and quality of life of the patients, online questionnaires will be provided.

In the control group (non-digital lifestyle management group), the patients will get the conventional postoperative care protocol without using the Noom application. To investigate the weight change and quality of life, variables are collected at baseline, 4 months, and 6 months after surgery.

Inclusion Criteria:

• Target: Among the patients who have undergone thyroidectomy, patients who are interested in weight management and can use the Noom app by themselves or with the help of neighbors.
• The patient has 23 or more BMI at the time of enrollment.
• In The Situational Motivation Scale (SIMS), a total of five stages of synchronization level of 68 or higher, which is the top 40% of the 112 points (1st stage: pre-consumption stage; stage 2: deliberation stage; stage 3: preparation stage; stage 4: action stage)
• The patient agreed about participating in this study.

Exclusion Criteria:

• The patient was diagnosed with chronic diseases (hepatic disease, kidney disease, diabetes, etc.).
• In the case where there is no member who can support among family members,
• The patient who is not a smartphone or has difficulty using digital technology.
• When it is difficult to lose weight (pregnancy and pregnancy preparation, breastfeeding, and less than 12 months after childbirth)
• If the patient has a history of psychiatric illness (eating disorder, depression, etc.).
• If the patient is taking diet-related drugs or health supplements, or treatments.
• If there is a restriction on physical activity (not allowed to exercise for more than 30 minutes a day).