45 Pounds (More or Less), by K. A. Barson

Ann has tried plenty of diets, but they never seem to stick.  Whatever weight she loses, she manages to put back on.  But this time will be different.  Her aunt is getting married and Ann is committed to the idea of losing 45 pounds before the wedding, so she can fit in a decent dress.

What emerges is a story about Ann's relationship with food, how it serves as a surrogate for love, how it defines not only her health but her self-image, and all of the ways that popular culture both shames the overweight while also encouraging people to over indulge.  Along the way, Barson shoehorns in messages about anorexia and other eating disorders, and examines how even young children are susceptible to unhealthy messages about eating.  It's a lot to fit into a book and the results can at times become preachy.  That's a bit of a shame since Ann makes a very appealing protagonist and her struggles are easy to relate to.