It's a severely restrictive diet that really shouldn't be attempted without careful guidance of a medical professional. It starts as a very low calorie diet, and remains low calorie throughout. It's a semi-starvation diet that may be advisable if you are grossly obese and it is recommended by a doctor.
It's not sustainable long-term.
Web MD has a good, detailed article on it: www.webmd.com/diet/features/the-rice-diet-