As it is a somewhat cornerstone of your pitch, I can't help but comment on the use case.
For the simple reason that any person's gut microbiome - which varies considerably and is the focus of intense research as too little is yet known - both consumes and modulates the processing of calories, counting calories is generally considered bad science and an entirely ineffective way to measure, guide or sustain a healthy lifestyle [1][2][3].
Personally, I think unless you're diabetic, in which case you'd anyway rely on an entirely different monitoring/ tracking system, it's just a whoefully ineffective KPI.
Most people today for example rather grossly undersupply fiber. If an app could deduce contents of calories, fiber and fat contents of a meal and track healthy composition/ supply for each, that would truly support a healthy lifestyle.
1: https://www.health.harvard.edu/staying-healthy/stop-counting...
2: https://www.scientificamerican.com/article/science-reveals-w...