This is a process Brazilians know well. Chocolate bars used to have 200g. Some now have less than 100g. Toilet paper rolls used to have 50m; most now have 30m and some have only 10m. This sort of thing started happening in the 1980s, because the government had frozen prices (that always works well). It became such a problem that now the law says that the packaging must clearly point out if the quantity inside has cha…
I'd also like to see a law passed that requires each product to mention on its packaging if its ingredients (even just their relative proportions) have changed. This would apply to things like foods/drinks and also cleaning products. Of course companies would protest, claiming that their recipes are trade secrets, but we already require that products list their ingredients, and we protect trademarks for products, whi…
Note that a lot can be told just looking at the label, but few people do it. For example quality meats tend to have more protein, quality diary products tend to to have more fat. High salt and sugar is usually a bad sign.
The order of ingredients is important too: greatest amount first. It means that if the thing they advertise in front of the package is way down the list, that's not good.