The plan involves eating food which is high in fats, low in carbohydrates and some protein - and it's clearly working for Fury.
The Gypsy King scoffs 3,500 calories - about 1,000 more than is recommended for the average male - across seven meals in a day.
A typical breakfast for Fury is low-carb rye bread, avocado, eggs and lean bacon. He has to avoid foods containing sugars, like tomatoes.
Explaining how he makes Fury's diet and training work together in sync, Marriott told Sky Sports: "He's on a 'targeted keto' diet so we know exactly how much carbohydrates to give him.
"We give him a high-glycaemic gel, like cyclists use, which powers him through an hour training session.
"After the session he goes back into ketosis, because as soon as you have carbohydrates on a ketogenic diet, you need a different fuel source.
"When he's done an hour's session, the carbohydrate is out of his body, he utilises a different fuel source which burns fat."
Marriott admits that Fury is finding his new diet 'hard', but insists the undefeated star is remaining strict as he gears up for a return to the ring by training in Marbella.
Fury, who is only doing low intensity training at present, will up his calorie intake to 5,500 a day - more than double the average man - when he steps things up.
And if he continues to hit targets and reach his goals then he can look forward to his cheat meal of choice - fish and chips.
Marriott added: "Tyson, if he sticks to the plan, will be allowed treats. If you do this diet right, you can have a cheat meal.
"If it's done right, you can get away with eating as much rubbish as possible within a three hour window, and it actually burns fat. But you can't do that every weekend!
"Tyson will be getting a few good meals, trust me. Everyone thinks dieting is doom and gloom and you can't eat anything but, the way I work, you can. You need to feed the mind, and you need a healthy mind before you fight."
