additional protein during diet is muscle sparing

i think this goes without saying but nonetheless:

Med Sci Sports Exerc. 2009 Nov 13. [Epub ahead of print]

Increased Protein Intake Reduces Lean Body Mass Loss during Weight Loss in Athletes.
Mettler S, Mitchell N, Tipton KD.

1School of Sport and Exercise Sciences, University of Birmingham, Birmingham, United Kingdom 2Department of Agricultural and Food Sciences, ETH Zurich, Zurich, Switzerland 3English Institute of Sport, Sheffield, United Kingdom.

PURPOSE:: To examine the influence of dietary protein on lean body mass loss and performance during short-term hypoenergetic weight loss in athletes. METHODS:: In a parallel design, 20 healthy, young resistance trained athletes were examined for energy expenditure for one week and fed a mixed diet (15% protein, 100% energy) in the second week, followed by a hypoenergetic diet (60% of the habitual energy intake), containing either 15% (~1.0g.kg) protein (control group, n=10; CP) or 35% (~2.3 g.kg) protein (high protein group, n=10; HP) for two weeks. Subjects continued their habitual training throughout the study. Total, lean body and fat mass, performance (squat jump, maximal isometric leg extension, one repetition maximum bench press, muscle endurance bench press and 30 sec wingate test) and fasting blood samples (glucose, non esterified fatty acids (NEFA), glycerol, urea, cortisol, free testosterone, free IGF-1 and growth hormone) and psychological measures were examined at the end of each of the four weeks. RESULTS:: Total (-3.0 +/- 0.4 kg and -1.5 +/- 0.3 kg for the CP and HP, respectively, p=0.036) and lean body mass loss (-1.6 +/- 0.3 kg and -0.3 +/- 0.3 kg, p=0.006) were significantly larger in the CP compared to the HP. Fat loss, performance and most blood parameters were not influenced by the diet. Urea was higher in HP and NEFA and urea showed a group*time interaction. Fatigue ratings and 'worse than normal' scores on the DALDA were higher in HP. CONCLUSION:: These results indicate that ~2.3 g.kg-1 or ~35% protein was significantly superior to ~1.0 g.kg-1 or ~15% energy protein for maintenance of lean body mass in healthy young athletes during short-term, hypoenergetic weight loss.