I already edited and answered in another comment. The actual studies (especially large meta-analyses) show very good results between 6 and 7, I was just thinkin

I already edited and answered in another comment. The actual studies (especially large meta-analyses) show very good results between 6 and 7, I was just thinking of linking this for the overrecomendation of 8-9 and copied it by mistake. Though even here they try to reccomend more in the abstract than what their results suggest, so look at the actual results e.g. all-cause mortality.