Simplify and improve section for adding nutrient values

[zanovis]

Problem

The Edit Nutrients section is a bit overwhelming for new users and leads to some confusion due to values not translating if toggles are changed.

Proposed solution

1. Is there value in having a distinction between 'Nutrition as sold' vs 'Nutrition for prepared product'? If not, I suggest removing the option to select one or the other to reduce friction. I imagine most products list nutrition 'as sold'.

2. Can we use defaults in the nutrition fields to the user's region defaults? So for US users, the default would be 'per serving' (Similar to: User Preference for 'per 100g' vs 'per serving' toggle smooth-app#3615). I believe we are taking in US 'per serving' values, and normalizing to 'per 100g'. How is this being calculated if the product doesn't have 'serving size' nor 'product_quantity'? In the EU, I think this would remain 'per 100g'.

3. Can we translate the values from 'per 100g' values to 'per serving' values if the radio button is switched? Currently, it does not translate.

Mockups

Not exactly like this, but to give you an idea:

Part of

openfoodfacts/smooth-app#3615

[CharlesNepote]

1. Is there value in having a distinction between 'Nutrition as sold' vs 'Nutrition for prepared product'? If not, I suggest removing the option to select one or the other to reduce friction. I imagine most products list nutrition 'as sold'.

Yes there is value to do this because:

• this not make sense to display 'as sold' values for a syrup or any kind of product which has to be prepared; this represents dozens of thousands of products; eg.
  • 9000+ https://world.openfoodfacts.org/category/dried-products-to-be-rehydrated
  • 7200+ https://world.openfoodfacts.org/category/syrups
  • 1900+ https://world.openfoodfacts.org/category/tea-bags
  • ...
• people following low calories diets need to know the values for the prepared product
• many products do display nutrition facts for the prepared product (at least in Europe)
• here in Europe the Nutri-Score is computed based on the prepared product; might be the same in Latin America for black octagons labels; etc.

A solution could be to remove [ ] for 100 g / 100 ml [x] per serving when Nutrition for prepared product is unchecked.

2. Can we use defaults in the nutrition fields to the user's region defaults? So for US users, the default would be 'per serving'

Yes I think it would be a very good idea.

3. Can we translate the values from 'per 100g' values to 'per serving' values if the radio button is switched? Currently, it does not translate.

Yes it's not translated because in many cases the values per_100g are in fact per_serving and should not be translated. Sometimes people are entering values per 100g but forgot to check 'per serving': if they check after they have filed the values they won't be happy if the values are translated...

It would be interesting to see if the majority of issues needs to translate the values.