The need for your app is overwhelming. I am 65, female, very fit, and lost 40 pounds since 2014.
Daily, I do some type of class, either strength, cardio, yoga, or walking. Here are my concerns with your app as a vehicle to long-term improvement.
1. The enemy of healthy living is social interaction that is nearly always alcohol and food indulgence. Either your user has to find new friends (like an alcoholic develops a cohort of non-drinking friends,) or they have to acquire the strength of purpose to abstain while still being social. Success here is very dependent on self-esteem....a distinctly non-technical aspect not directly addressed by the app.
2. Preparing your next meal BEFORE YOU ARE HUNGRY is critical to success. This could be addressed by subscribing to a pre-packaged frozen meal service, or, by consistently doing grocery shopping and meal prep in advance. The latter takes planning, discipline, and effort. Lack of planning is frequently the reason for eating excess or unhealthy food.
3. Eating to self-soothe is prevalent. Learning other sources of pleasure or gratification is crucial to sustained success. For example, I always want second helpings even though I know I have already had enough. This because my stomach needs an extra 15 minutes to tell my brain that I am satisfied. To cope, I set a 15 minute timer and for that 15 minutes, I walk away from the food area, sit in a comfy chair and do something pleasant with my phone, such as read fashion news or text with a friend. A sine qua non of healthy eating is having a list of other pleasant things to do when you feel the urge to eat when not hungry.
4. Many overweight people will only succeed in the transition to a healthy life if they have in person contact with others that support and acknowledge their struggle. Either a 12-step meeting or a FaceTime call with their coach is vital so that your user can visualize that person's face when the user is at the moment of decision to binge or not.
5. If you take away food and drink as the emotional coping tool, you have to replace it with something that is not self-destructive. Your users have to be ready when emotional crisis comes when, then more than ever, they will feel entitled to eat or drink anything within convenient reach. For this reason, I am unable to keep ready-to-eat foods in my house.....cereal, cheese, nut butters, dessert, snacks, bread of any kind. I do keep fresh apples and oranges, but that is it. Your user must develop other methods of dealing with crisis.....journaling, phone a friend, or just giving themselves permission to withdraw, lay down and rest if possible. Since I have momentum on my side, an activity that 100% occupies the mind, like a spin class, is my helper that enables me to muddle through. Meditation is another good tool.
I have come to believe that lack of self-care has much more to do with emotional self-regulation and self esteem than it does with lack of knowledge on sleep, exercise, and nutrition.
However, for those who suddenly get motivated by a health scare, the knowledge and guidance in your app is like a welcome breath of life.