You should try contacting people with regular health problems like people with obesity, diabetes, aids. Another group that can provide you good ideas is high-p

You should try contacting people with regular health problems like people with obesity, diabetes, aids. Another group that can provide you good ideas is high-performance athletes. You definitely need something that is a device or is installed on a mobile so people can add information without having to move to a website. On the website you could show progress, suggestions and recommendations based on the aggregated data.