A recent study buttresses one explanation for the rise of depression and heart disease in recent generations: an increase in processed vegetable oil in the diet. Doctors at Ohio State University measured blood ratios of omega-3 to omega-6 fatty acids and found....
The more omega-6 fatty acids people had in their blood compared with omega-3 fatty acid levels, the more likely they were to suffer from symptoms of depression and have higher blood levels of inflammation-promoting compounds.... The 6 individuals diagnosed with major depression had nearly 18 times as much omega-6 as omega-3 in their blood, compared with about 13 times as much for subjects who didn't meet the criteria for major depression.
That's a striking correlation.
Omega-3 fatty acids are found in foods such as fish, flax seed oil and walnuts, while omega-6 fatty acids are found in refined vegetable oils used to make everything from margarine to baked goods and snack foods. The amount of omega-6 fatty acids in the Western diet increased sharply once refined vegetable oils became part of the average diet in the early 20th century.
According to the Vegetarian Society of the United Kingdom, a reliable source of omega-3 is ground flax seed. Tofu, apparently, is only so-so.