54 carbs per day in grapefruit juice is a lot of carbs. I suspect grapefruit isn't the miracle product it's cracked up to be. OK, it has vitamin C and other vitamins, but it also has a lot of sugar. I don't know anything about the Mayo diet (except that it has absolutely nothing to do with the Mayo Clinic), but if I were you, I'd scrap the juice, or at least cut it WAY down.

Just my humble opinion.

Rachel