Thank you for linking the study.

Some good news from it. If you weigh the food instead of depending on the package size then the labels become much more accurate!!

"Serving size, by weight, exceeded label statements by 1.2% [median] (25th percentile −1.4, 75th percentile 4.3, p=0.10). When differences in serving size were accounted for, metabolizable calories were 6.8 kcal (0.5, 23.5, p=0.0003) or 4.3% (0.2, 13.7, p=0.001) higher than the label statement."

If you look at the table "Deviation of metabolizable calories from label calories" [https://pmc.ncbi.nlm.nih.gov/articles/PMC3605747/figure/F1/] you'll see that most labels even for service side are pretty good and there are some that are really bad.

If you'll look at one of the worst offenders Tostitos, the label has "Tostitos Tortilla Chips - serving size 24 chips", but chips vary a lot in size, so you could have a huge variance in weight. If instead you weighed them, which I do with my chips, I bet the calories are much closer to the label.

Body composition comes down to routine. I've found found I love to eat, but I pretty much eat the same meals week over week, that makes it extremely easy for me to lose or gain weight depending on my goals.