A study conducted by Clapp J et al and published by Preventing Chronic Disease investigated the serving size, calories and sodium content of processed foods with the top 80% of sales between 2009 and 2015 in America.
Results were reported per serve and density and it was found that sodium per serve and density decreased by 7.6% and 6.0%, respectively. Serving size, calories per serving and calorie density also decreased, although by smaller percentages.
Authors viewed these results as positive, in that food industry are reformulating for both sodium and total energy of processed foods.
Read more here.