Omega-6s are pro-inflammatory, while Omega-3s have an anti-inflammatory effect.
We evolved genetic patterns established on a diet with a ratio of omega-6 to omega-3 essential fatty acids (EFA) of approximately 1 whereas in Western diets the ratio is about 16. This high ratio promotes the pathogenesis of vascular disease, cancer, and inflammatory and autoimmune diseases, whereas lower ratios exert suppressive effects. For example, in the secondary prevention of cardiovascular disease, a ratio of 4/1 was associated with a 70% decrease in total mortality.
A distorted ratio of these polyunsaturated fatty acids may be one of the most damaging aspects of the Western diet.
The plot above illustrates the ratio of omega-3 to omega-6 for some select foods.
Typical green vegetables contain the ratio experienced by our primate ancestors. Legumes are acceptable sources for these essential fats as well. Flaxseeds have an extraordinary favorable content of these nutrients and can be used in small quantities to assure adequate intake (a teaspoon crushed in smoothie or on salad, as examples).
 Simopoulos, A. (2002). The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomedicine & Pharmacotherapy, 56(8), 365-379.