jess This is a quite interesting overview which I won't pretend to understand in its entirety 
www.ncbi.nlm.nih.gov/pmc/articles/PMC2235907/
It does point out that research has been confined to laboratory animals, but highlights the difficulty of defining addiction, and prefers the term dependency, and also cites some anecdotal evidence from patients:
'Neural systems that evolved to motivate and reinforce foraging and food intake also underlie drug-seeking and self-administration. The fact that some of these drugs can cause addiction raises the logical possibility that some foods might also cause addiction. Many people claim that they feel compelled to eat sweet foods, similar in some ways to how an alcoholic might feel compelled to drink.'
and
'The concept of “sugar addiction” has been bandied about for many years. Clinical accounts of “sugar addiction” have been the topic of many best-selling books and the focus for popular diet programs (Appleton, 1996, DesMaisons, 2001, Katherine, 1996, Rufus, 2004). In these accounts, people describe symptoms of withdrawal when they deprive themselves of sugar-rich foods. They also describe food craving, particularly for carbohydrates, chocolate, and sugar, which can trigger relapse and impulsive eating. This leads to a vicious cycle of self-medication with sweet foods that may result in obesity or an eating disorder.'
I'm not sure however, that it reinforces the suggestion that obesity resulting from sugar or food dependency is a disability.