Pubmed has a lot of abstracts pertaining to metabolic rate: http://www.ncbi.nlm.nih.gov/pubmed/18198305 "Body weight is defended in non-obese participants during modest caloric restriction, evidenced by metabolic adaptation of RMR and reduced energy expenditure through physical activity." There are plenty of other studies that support CR as a factor in lowered RMR. I read one (can't remember where) that used non-obese women. IIRC, the women on 300kcal deficits had no change in metabolic rate, while those on 500 did.