LTS...very important question!

I have not seen any such study, but similar questions arise over various manufacturing/recycling/use issues. (CFC light bulbs, diapers, plastic bottles...etc.)

In the case of bidéts, it might well be a regional issue dependent on water supply.

A few years ago in California, there was a serious drought & water shortage, causing lawn watering bans...and eventually the instruction went out.."Don't flush for 'everything'". People saved so much water that the pumping stations had be reprogrammed. Of course, once restriction were lifted, it was back to "business" as usual.

I have several toilets in the house, including one in a back-basement location (near my workshop)where I can use that rule and only flush once a day. It saves a LOT of water...4 gallons X 6-8 flushes? (I don't actually count)

Obviously, men use only about 10% of the TP manufactured, and I will make no suggestions about how women's share might be reduced.