It's always hard not to notice when a show's regular cast suddenly gains or losses weight. Body weight fluctuations affect women more than men due to pregnancy, post-pregnancy and sometimes, sadly, due to health issues. The latter reason applies to Anna Gunn, who gained a noticeable amount of weight in Breaking Bad’s last season.
In fact, the weight gain began in season 4, leading die-hard fanatics to speculate the reason as to why that is. For some, myself included, the obvious explanation was that she gained baby weight. But the real reason for Gunn's change of physique was far from what spectators thought and pretty sad too.