It sounds like a silly question. I ask it to stir up some thought on the purpose of exercise in the Christian's life. I started using the P90X system a few weeks ago and it is brutal. I have been losing weight slow and steady using biblical principals, because I wanted to be obedient to God's Word. Over the last two years I have lost almost 60lbs. The weight loss is not the important point, it occured not because I wanted to look and feel better (those are side benefits), but because it is important to obey God. God's Word plainly states that physical exercise is of some value, but spiritual exercise is of great value. We cannot, contrary to popular opinion, add a single day to our life. Our days are ordained by God. God can and will extend our time on earth if we obey His Word in certain areas (like obey and honor our parents). So why should we bother to wear ourselves out? My reasons are circulation, muscle tone, strength and energy. Exercise has value, but we should not decive ourselves. It does not add to our days. I may be feeling much better when I torture myself, but it is desided by the Lord when I will leave the earth. I live by His good pleasure. I should obey His Word regarding overeating, but make no mistake, rice cakes and power bars are just food choices. They will not extend my life (rice cakes aren't real food anyway).
Trust in the Lord, not protien shakes.