Low Carb Perennials

I find that I do best on a low-carb diet and I was wondering if anyone knew of any Low Carb Perennials I could plant in Pennsylvania - Zone 6.

Everything that isn't a root, tuber, or grass. 

Nuts to you!!

Lovage.

Pecans can be grown in part of PA. Walnuts and hazelnuts are also good options.

http://www.emmitsburg.net/gardens/articles/adams/2002/grow_your_own_pecan_trees.htm
http://www.pnga.net/

Acorns and chestnuts are high carb, but most other nuts are largely oil, with significant protein and not very much carbohydrate.

One problem with nut trees is that they are rather large, and take a while to start bearing. Hybrid hazelnut breeders are working to get around this - they have shrubby varieties that only take 3 or 4 years to get a good crop, but that is still experimental.

Here's a listing of perennial vegetables for cold temperate climates:  http://perennialvegetables.org/perennial-vegetables-for-each-climate-type/cold-temperate-east-midwest-and-mountain-west/

Any of those for roots and tubers will be high-carb.