My ob/gyn told me that sugar, as well as caffeine, can cause imflammation in breast tissue. I have fibrocystic tissue. The avoidance of sugar, caffeine, red meat, soy, and the addition of iodine-rich foods has eased the soreness, hardness, and discomfort from swelling.

I wonder if you've managed to boost prolactin somehow by eating sugar. Increasing calcium intake might help.

I have been paleo for about 6 months. After the first few months, my breast size went down over a cup size... Last month, I got a little sloppy with my diet- taking in more sugars,eating more red meat, and just more conventional meat in general. My breasts were tender, slightly uncomfortable, and a little fuller (not back to the previous size, but still noticeably fuller). For the last 2-3 weeks, I have limited my sugars again, almost cut out conventional meat entirely, and decreased my red meat intake back to maybe once a week. I am glad to say the tenderness is gone completely... and unfortunately, the inflammation lol... this was like my unplanned, quick/short-term, personal experiment of the effects of sugar and red meat on breasts :D