If January is the month of dietary advice, it is worth listening to Nacer Chadli and his story. Chadli has been one of the surprise players of the season, making himself indispensable to Tottenham Hotspur in a way that few predicted.

Chadli is lighter, quicker and stronger than he was last season. He is a better player, more useful to the team and one of the men Mauricio Pochettino will always count on when it matters. His is a story of individual improvement, of seizing a chance that could have slipped away. Chadli puts it down to a new focus and his new diet, devised at an Italian health centre in July.

“I was learning there how to eat the best way, because you have to eat a certain way to help your body recover as fast as possible,” recalls Chadli, who was recommended Hotel Merano by Mr and Mrs Vincent Kompany, while Karim Benzema has also been there. “They take your blood and analyse what you can eat, what your body can’t handle or afford.”

The result is that Chadli is now dairy free. “They gave me advice, and I don’t drink milk any more. Only sometimes soya milk. And I don’t eat cheese.

“I eat a certain amount of fruit and vegetables, and it is better to eat fruit before a meal. Normally, I was eating fruit after as a dessert, but it is better to eat it before. I am allowed to eat meat one or two times maximum a week, and for the rest a lot of fish and chicken. I think it has helped me,” Chadli adds. “I lost a bit of weight.”

Chadli returned to pre-season with Tottenham just 17 days after Belgium were knocked out of the World Cup, but determined to prove a point.

“I was mentally stronger this year to come back after a disappointing first year at Tottenham,” he admits. Swansea City and Olympiakos had tried to sign him last January but in the summer he was insistent, refusing to listen to offers so he could stay and fight for his place. “I don’t want to leave a club like this. If ever I leave a club I want to leave it, as we say in French, par la grande porte, not by the back door.”

Pochettino told Chadli that every player would have a chance to prove himself, which is precisely what he wanted to do. “After the holiday I wanted just to clear my mind and come back and train,” he says. “I just went to training, I wanted to be as fit and fast as possible. After two and a half weeks I was playing my first minutes of the season. I wanted to take the chance and I did.”

This meant that when Chadli started Pochettino’s infamously challenging pre-season sessions, he was well equipped to take them on, thanks to his rehabilitative summer. Chadli is certainly at home discussing health and fitness, and is talking to me at Wood Green Library, north London, where the Tottenham Hotspur Foundation delivered its 2,000th NHS health-check in the community. “It is good to see people take care of themselves,” Chadli says, “and to know what might happen without checking.”

All of the hard summer running Pochettino demanded came quite naturally to Chadli, who has been a good athlete but was now even fitter. “It was very hard,” he remembers, “but it was good for me because my body could handle it. And if your body can handle it then you become stronger. For me, it was perfect to have a hard pre-season, even if it was not a long pre-season. It would be better to have maybe two weeks more, to fully load my body, but it was pretty good for me to have that training.”

Chadli’s words are softly delivered but he speaks with the focus and assurance of a man whose hard work is paying off. Not all of Spurs’ 2013 signings are delivering on their transfer fees, and no player can replace Gareth Bale. But Chadli’s £7m fee is now looking like a smart investment.

He joined from FC Twente, where he had played under Steve McClaren, a “good manager” whom he hopes to face in the Premier League next season, should Derby County be promoted. While he sees some similarities in the attacking approaches of Pochettino and McClaren, Chadli is new to this intensity of physical preparation, and he likes it: “We did not train as hard in Holland as we do now, as the physical aspect is not as important. It’s different. It is good for us to train like this, we are fitter than the other teams.”

That much has been clear for a while, and Chadli is fitter than most. Thanks to his new diet, his determination to stay and his willingness to embrace the new regime, he has become exactly the type of player Pochettino wants. He follows instructions, works ferociously hard, in and out of possession, gets into the box and scores goals. He already has seven in the Premier League. Eden Hazard is the only wide player with more.

After a brief substitute appearance in the Europa League at AEL Limassol, his first game back, Chadli was trusted to start against Queen’s Park Rangers at home on 24 August. Stationed out on the left, but breaking into the box, he scored twice and has not looked back. “My first game helped me a lot, to score twice to build my confidence,” he says. Chadli refuses to divulge “the secret” to his role but, in short, it involves a lot of running. Against Chelsea on New Year’s Day, when Spurs won 5-3, Chadli hit the post before Danny Rose scored the second, and scored the deflected fifth himself.

Chadli faced real competition in August for those three berths in Pochettino’s 4-2-3-1. Gylfi Sigurdsson has been sold, Lewis Holtby has gone out on loan and Chadli has forced his way in front of Aaron Lennon, Andros Townsend and Erik Lamela. Of Spurs’ attacking midfielders, only Christian Eriksen has started more games.

Much of this owes to Chadli’s work without the ball, the famous high press which is so important to Pochettino’s style. He reveals how the players are told to “press directly for the first three seconds” before recovering their positions, and he is very good it. “I am fitter, I play almost every game this season,” Chadli says. “The manager has confidence, and this gives me confidence.”

Chadli has scored nine goals for Spurs this season (GETTY IMAGES)

Chadli is obviously very happy at Spurs, as anyone would be who is at the heart of an improving team. But he also has friends there, who share an unusual hobby: board games. While the whole Spurs squad play Mario Kart on Nintendo DS – Kyle Walker is the best, then Kyle Naughton and Rose – a smaller group play perudo – a dice game – or something different.

Settlers of Catan is a German, four-player strategy game which Jan Vertonghen introduced to Tottenham. Vertonghen, Chadli, Mousa Dembélé and Benjamin Stambouli play it at the training ground and at away games. For now, Vertonghen is the best, but Chadli is determined to catch him up.

“Jan has the most experience of this game,” Chadli admits. “He played a lot of with his brothers and his friends. I didn’t play it so much, now I am learning with my friends and brothers, too. When I play more, I think I am going to beat him.” There are always things left to improve.