Bright yellow urine can occasionally happen during the program and should not be alarming. The bright yellow urine can be due to the B Vitamins in your supplements being excreted. B vitamins are water soluble so what you don't absorb is excreted in the urine. However, if your cells are more hydrated then more of the B vitamin can get to the cells. This is why it is so important to drink at least half your body weight in ounces of water everyday. It's also a reason for you to be sure that you are drinking the right water source that has good minerals in it.