It needn’t be exact. A ballpark calorie/sugar that’s 90% accurate would be sufficient. There’s some research that suggests that’s possible: https://arxiv.org/pdf/2011.01082.pdf
But what use would it be then, you wouldn’t be able to compare one potato to another, both would register the same values.
I think the use case is not people doing potato study but people that want to lose weight and need to know the amount of calories in the piece of cake that’s offered at the office cafeteria.
And that means the feature is useless, there are so many things in a cake that can’t be seen from a simple picture.
And if it is just a generic “cake” value, it will show incorrect data