Some studies are showing that frozen vegetables have higher nutrient content than fresh, because they're frozen when ripe, while fresh is picked before ripe and decays during transport. is this true?

Depends on the : Veggies tested & the practices of the grocer/purveyor who sells them (how long are they kept before sale/disposal, in what condition?, where were they grown & how long did they spend in transit, etc). Don't get overwhelmed with these issues tho, step 1. Increase your vegetable intake (esp green veggies. In whatever form YOU like them & are most likely to eat them). If u can do that, ur doin great!