What is diet fuel ultralean the usn diet fuel ultralean is quite simply a high protein and high fibre meal replacement shake that can offer you a convenient meal on the go this can in turn help you to not only maintain a diet thats balanced but improve on what you currently eat on a daily basis and ensure that you are getting great quality and essential nutrients into your body what are the benefits safe and healthy weight loss along with the maintenance of a healthy body and mind are best