The `America`s Got Talent` host - who was hospitalised with kidney failure and blood clots on his lungs before being diagnosed with autoimmune disease lupus nephritis earlier this year - has made radical changes to his diet in order to stay healthy.
He said: "I feel better than I`ve ever been. I`m in the best shape that I`ve ever been in.
"Since this whole thing has happened, I haven`t had any salt, red meat, fastfood. [I`ve only had] chicken and fish. I feel so great. I`m juicing a lot."
The 31-year-old star and wife Mariah Carey will celebrate their twins Moroccan and Monroe`s first birthday on April 30, and are planning to head overseas as a family.
He said: "It`s amazing. It goes by so fast. We`re going away. We`re taking a break. It`s going to be exciting. We`re doing something special and something unique."
But with their increasing age comes increasing mobility, much to Nick`s terror.
He explained to People Magazine: "They`re trying to walk and I`m nervous because they`re at that age when anything can happen.
"My son has this thing where he loves banging his head and crushing stuff. Something new is happening every day."