The last mechanism that I want to talk about is essential fatty acid metabolism. These are the polyunsaturated fats. Alpha-linolenic acid is the essential fat on the omega-3 side, and linoleic acid is the essential omega-6 fat, but then you have the longer-chain derivatives of these, EPA and DHA on the omega-3 side and arachidonic acid on the omega-6 side. The reason these are so important is that essential fatty acids influence prostaglandin production, and prostaglandins modulate hormone receptor site sensitivity and the proteomic response that happens when a hormone binds to the receptor. Too much omega-6, for example, can lead to altered hormone receptor function, and this omega-6 linoleic acid is found in industrially processed plant oils, like soybean and corn oil, safflower, sunflower. These are oils that are typically found in processed and packaged foods, chips, anything fried, a lot of restaurant foods, but certainly most foods that come in a bag or a box, which comprise a disturbingly large percentage of calories for the average American. And EPA and DHA are found primarily in cold-water fatty fish and shellfish, and a fairly large percentage of people are not eating enough of this preformed EPA and DHA.
Hulshoff Pol et al. (2006) studied the gross brain volume of 8 male-to-female transsexuals and in 6 female-to-male transsexuals undergoing hormone treatment. They found that hormones changed the sizes of the hypothalamus in a gender consistent manner: treatment with male hormones shifted the hypothalamus towards the male direction in the same way as in male controls, and treatment with female hormones shifted the hypothalamus towards the female direction in the same way as female controls. They concluded: "The findings suggest that, throughout life, gonadal hormones remain essential for maintaining aspects of sex-specific differences in the human brain."