I agree RRR if not RN!

I agree Chris, that is a vital post which should be read by anyone considering a predominately or exclusively non meat diet.

As you pointed out, one culprit may well be Omega-6's.  Most of us have far too much omega 6 and too little omega 3's. Since the two do compete, it is entirely possible that a person could consume adequate omega 3 and yet derive very little benefit due to an imbalance in omega 3 to omega 6 consumption.

To quote Dr. Mirkin:

For most of the time humans have been on earth we have eaten foods containing omega-6's and omega-3's in a ratio of about 2:1. However, over the last 50 years in North America, the ratio has changed to from 2:1 to 10-20:1. Our diet now includes huge amounts of oils that are extracted from plants and used for cooking or in prepared foods. These oils (such as corn oil, safflower oil, cottonseed oil, peanut oil, soybean oil) are primarily omega-6s. We have decreased our intake of omega-3's, found primarily in whole grains, beans and other seeds, and seafood.

Eating too much omega-6 and too little omega-3 causes clots and constricts arteries to increase risk for heart attacks, increases swelling to worsen arthritis, and aggravates a skin disease called psoriasis. It may block a person's ability to respond to insulin, causing high insulin and blood sugar levels and obesity. It increases hormone levels of insulin like growth factor-1 that causes certain cancers.

To get your ratio on omega-6s to omega-3s back to a more healthful 2:1, eat seafood, whole grains, beans and other seeds, and reduce your intake of foods made with or cooked in vegetable oils.

http://www.drmirkin.com/nutrition/9483.html