How healthy is Trader Joe's? Well, you could ask that question about ANY brand. If you go into Trader Joe's and buy the pre-made frozen meals, of course they are going to be high in fat, sodium, calories, etc. If you go into Trader Joe's and buy organic fruits, veggies, etc, then you could say it is a healthy place to shop.
I personally LOVE Trader Joe's but I don't go in there and buy some of their convenience items. I usually buy their fruits/veggies/salad mixes, hummus, cheese, beans and some meat (love their lamb).
All grocery stores stock healthy and very unhealthy items. It is your choice to purchase what strikes your fancy, be it a healthy item or not.