In the present proposal, the effects of surgery and cancer will be examined by comparing subjects undergoing breast surgery because of malignancy vs. prophylactic reasons (aim 1). Furthermore, the effects of one-week pre-operative protein feeding with or without enrichment with arginine on post-operative protein metabolism (aim 2) will be investigated in the cancer group. Variables of interest are: 1. Whole-body and skeletal muscle protein metabolism, whole body arginine turnover and de-novo arginine production rate, and the anabolic capacity to feeding(assessed by stable isotope methodology). 2. Body weight, muscle mass and functional status, score for well-being (assessed by Profile of Mood State and Mini Mental State).