Calories in Beef loin, tenderloin roast

What makes beef loin so powerful?

The psoas major muscle, which forms the beef tenderloin, sits deep inside the cow's rear quarter along the spine. Unlike muscles in the shoulder or leg, the psoas major bears almost no weight and performs minimal contraction during the animal's life. Because muscles toughen with use, this inactivity means the tenderloin contains very little connective tissue and minimal collagen. This anatomical reality is precisely why the cut is famously fork-tender and historically commands a premium price. Additionally, its remarkably low fat content—just over 6 grams per 100-gram serving—means it lacks the intramuscular fat, or marbling, that naturally bastes and flavors tougher cuts like chuck or brisket. To compensate for this inherent leanness, chefs frequently wrap tenderloin roasts in bacon or coat them in mustard and herbs before roasting. This technique introduces external fat and flavor during the high-heat cooking process. Without this added protection, the meat's minimal collagen means it can dry out rapidly if cooked past medium-rare.