Weight loss is associated with slower metabolism

"Meta-analysis of Resting Metabolic Rate in Formerly Obese People," by Arne Astrup, Peter C. Gotzsche, Karen van de Werken, Claudia Ranneries, Soren Toubro, Anne Raben, and Benjamin Buemann.

A meta-analysis of formerly obese people who lost their excess weight showed that they burned calories at a lower rate than people who were never overweight, according to a study in June's American Journal of Clinical Nutrition. This slower metabolism may explain why dieters have difficulty in keeping weight off.