An equivalent system, the nutri-score, have been showed to be extremely effective: https://en.wikipedia.org/wiki/Nutri-Score

On the french version of the page, it indicate:

> it also noted the following associations for the products purchased:

increase in overall food quality by 7.9%; 6% reduction in energy; 7.8% reduction in salt/sodium; 15.7% reduction in fat; 17.1% reduction in saturated fat;