Andy Ruiz Jr will begin a strict diet this week to prepare for his rematch with Anthony Joshua – but there will still be time for cheat meals at the weekends.

The first world heavyweight champion of Mexican descent beat Joshua earlier this year after weighing in at 19st 2lbs but plans to lose weight before the December 7 rematch, live on Sky Sports Box Office.

His personal nutritionist and chef, Zo's Meal Plans, exclusively told Sky Sports about how Ruiz Jr eats to maintain his fitness.

Ruiz Jr was over a stone heavier than Joshua

0:36 Andy Ruiz Jr says he's a 'nice guy' out of the ring but a 'destroyer' in it Andy Ruiz Jr says he's a 'nice guy' out of the ring but a 'destroyer' in it

Has Ruiz Jr stayed fit and healthy since beating Joshua?

He will be heavy but that's nothing we haven't dealt with in the past. He likes tacos. We don't worry about his diet outside of camp. Remember, this is a heavyweight camp. Andy isn't a lightweight.

When his diet begins, is Ruiz Jr disciplined?

Yes. We try to make it healthier. A lot of fruits and vegetables but he has the occasional treat. For the most part, he is serious about his diet. We try to give him the correct fuel to get through his training sessions. We introduce veggies and fish.

Tell us about Ruiz Jr's cheat meal…

During camp we will cheat. In the last camp we would go to the movies at the weekend and he would have popcorn. But the tacos are our getaway on Friday night, our cheat meal. There is a place we go to where he eats tacos. But nothing too crazy.

Where does Ruiz Jr go to eat tacos?

There is a place near his house, an outdoor area on the corner where you can't even sit inside - Andy loves the el pastor con queso tacos. They put cheese inside the taco, and melt it - we get an assortment but he loves the marinated pork.

Does a cheat meal keep Ruiz Jr focused during a training camp?

Definitely. We have to keep him happy. When he is hungry he gets grouchy. So I keep him fed. He works out very hard and his training days are rough so I keep him fuelled and happy.

A meal plan for an average day

We wake up and have an omelette with mushroom and spinach and avocado. I switch up the meats. Sometimes he asks for hash browns too. Breakfast

Andy likes to keep lunch lighter because he trains later in the day. He will have a chicken salad or a chicken wrap. Lunch

We have three full meals and snacks in between. He might snack on a wrap or a sandwich, something that he travel with. Andy has a lot of nuts and fruit too. Snack

Pasta or rice. We just left Saudi Arabia and Andy tried some rice there. He loved it, and now I have to try and replicate that rice! He likes the food in Saudi Arabia. Dinner

Steaks. He loves to eat steaks, man. Whenever we can fit in a steak, we do. We try to keep the steak leaner and I try to give him more chicken or fish, if I can. Meal of choice

Ruiz Jr vs Joshua II is on December 7, live on Sky Sports Box Office.