I find this very hard to believe, unless the term “trained professional” is quite broad. When I was much more into fitness and weighed every meal to the gram, I could tell if a bowl of cereal was a serving to within a gram or two.
In the study we gave people a variety of dishes to make their estimate on, some they were familiar with, some they were not.
The professionals were nutritionists who had trained in portion size estimation and were shown 2D images on a computer screen.
For what it's worth, we've had a lot of people who have claimed to be very accurate at portion size estimation from a long history of using a kitchen scale. We've paid many of them to do a quiz to see if they're above average accuracy and they have almost always ended up around 40% accuracy or worse.
We co-authored a paper on this with Google AI and showed it got about 2x the accuracy of a nutritionist because of it.
Thinking about it again, I'll probably do a lot worse from a picture because I can't have a bite of the food! Just having a spoon makes it so much easier in terms of ratios.
I guess, maybe cooks should have the best precision for this.
It’s possible to calibrate your estimates, but if you haven’t done that, it’s probably safe to assume you’re not particularly accurate.
Most people don't stay consistent in tracking long enough for any of this to matter, so really it's about what is the most accurate approach to achieve your goal and sustain longer term.
I wonder how good an ML model might be at that task. Maybe given a photograph of the plate and the menu description.