It doesn't all get converted to serotonin. In fact, when you take L-tryptophan in a supplement form, only about one to three percent of that administered is actually converted to serotonin. In contrast, when you take 5-HTP about 70 percent is converted to serotonin. 5-HTP is far more advantageous to raising serotonin levels than tryptophan. Beyond that, let's take a look at what I was describing earlier with the genetically-bred obese rats.
Many people inherit the predisposition to being overweight.
I just hope the word gets out there because it is an effective answer. The most severe cravings are the cravings that a bulimic person experiences. Bulimia is characterized by very, very low levels of brain serotonin. Typically, these women will consume large quantities of sugary foods, then, when they consume carbohydrates, the muscles in their bodies will uptake all the amino acids, with the exception of tryptophan. The delivery of tryptophan to the brain determines the manufacture of serotonin.