Listen I think the information you will find on [link removed by moderators] will be useful to you in building a Weight Tracker App on Thunkable. The Noom app is the product of the collaboration among nutritionists, personal trainers, and behavioral psychologists - creating an integrated approach which includes:
Food tracking using the Noom database
Logging of exercise, weight, blood sugar, and blood pressure
A personalized daily calorie allotment/requirement
One-on-one health coaching
Interactive tools to stay motivated