In this book, Dr. Barnard goes into detail about how certain foods affect not only our taste buds, but also our brains. Two of the most "addictive" foods are chocolate and cheese. In the past, research was conducted which showed that milk has very slight, but often detectable traces of morphine in it. They also found that small traces of codeine and other opiates could be produced in the cow's liver. It's theorized that Mother Nature uses theses opiates as a calming and bonding effect on baby calves (and baby humans, as it was shown that similar results applied to human milk as well).
So if you've ever suspected or sensed that you're addicted to some foods, perhaps you really are! The book goes into detail about all the possibilities and research that has been done in this area.
When speaking to people about plant based diets, it's very common to hear someone say "but I'll never give up my cheese!" And it's usually the very last thing to go, when converting to a full plant based diet.