Rio Ferdinand has experienced terrible loss in recent years. In 2015, his wife and the mother of his three children, Rebecca Ellison, died of cancer aged 34. Then in 2017 his mother, Janice St Fort, died from cancer too, aged 58. Now, he says, he is doing anything he can to ensure he and his children are not prematurely bereaved again.

So perhaps it is not surprising to find the former footballer promoting a DNA kit that claims to pinpoint the personalised exercise and nutrition needed for a longer life. Ferdinand is 40 now, and looks even stronger than he did when he was one of the best defenders in the world, an imposing, beautifully balanced ball-playing centre back who won 81 England caps and six Premier League titles with Manchester United. He is certainly bigger – 16kg (2st 7lb) heavier, a brick wall of a man, with arms like surfboards.

He may have been a supremely fit athlete, but now he says that throughout his playing career he was so skinny, he often felt weak. “You could see the fibres in my body when I was walking about when I played ’cos I was so lean.” The first thing he wanted to do after he quit football was bulk up – not least because he fancied becoming a professional boxer. He was refused a licence last year and gave up on that ambition.

There isn’t much that Ferdinand has not tried his hand at since he retired. He made a desperately moving documentary about life after the death of Rebecca, Being Mum and Dad; wrote an equally moving book about it with the journalist Decca Aitkenhead; started a clothing line; became a football pundit; campaigned against leaving the EU and knife crime; visited schools and prisons.

As well as the campaigning side, Ferdinand has always had a touch of the Del Boy about him. Sometimes it is hard to distinguish between Rio the crusader and Rio the wheeler-dealer. And today is such an occasion. He is flanked by a member of his sports management team and a publicist representing DNAFit, a nutrigenetics company that has created a simple saliva swab test it claims will transform lives. Nutrigenetics is an emerging – and as yet largely unproven – science that studies the interaction between genes and nutrition, with the hope of preventing disease.

We are in a small, claustrophobic office near London Bridge. Ferdinand seems to fill the room by himself. He is long and languid, tanned, with an immaculately strimmed beard. Suddenly, the room is even more crowded, as we are joined by a verbose businessman who speaks faster than anybody I’ve ever met.

“This is Avi,” says the publicist. “He’s here to explain all the technical stuff.” It suddenly feels as if I’ve been interview-bombed; I have a funny feeling that Avi is going to try to make this all about him.

Avrom Lasarow is a 43-year-old entrepreneur. His fulsome Wikipedia entry states that he left South Africa for the UK “where he began his career which ultimately led to a string of multinational companies”. Last April, DNAFit was bought by a Hong Kong-based genetics company, Prenetics, for $10m (£7.8m), and it appointed Lasarow CEO of Prenetics International. But enough of Avi. For now.

Ferdinand tells me of the enormous benefits he has reaped since being DNA tested. When he was trying to bulk up, he soon reached a ceiling, he says, and it was only after getting the DNAFit results that he realised he was doing everything wrong. “I wanted to gain weight, gain muscle mass and retain it. But I quickly hit a ceiling. I was knocking my head thinking: what’s going on?”

So what did he discover? “I was eating huge carbs and not enough protein and now my diet is much more balanced. Now I’m 101kg (15st 13lb), but comfortable. When I was playing I was 85kg (13st 5lb).” He also started to do more power than endurance work in the gym. I’m no expert, but surely you don’t need a DNA test to tell you a protein boost and lifting weights is an effective means of muscling up?

Many scientists believe we simply don’t know enough about nutrigenetics for companies such as DNAFit to deliver on its promises. Prof Eran Segal, a computational biologist at the Weizmann Institute of Science in Israel and a world leader in personalised nutrition, says: “Although this is an area of research that has potential, it is unclear whether the science is already there and thus far there is no evidence that it works.” But Ferdinand is convinced if he’d had this information when he was playing, he would have had an even more distinguished career. “Trust me, I would have been able to play longer, I would have got 100 caps.”

How else has the DNA test helped him?“ Alcohol,” he says. “If you’re doing it in moderation … ” He looks at Lasarow. “What is it, a drink a day?”

“A glass of wine a day is good for you,” Lasarow says. “For instance, in Rio’s case he has a certain genome type, so alcohol in moderation increases good cholesterol.”

Ferdinand says that while he and his fiance, the former Towie star Kate Wright, like to set a good example to his kids by eating healthily, he has in no way become a food fascist. “I go to a kebab shop on a Friday and I like a pint of Guinness, a whisky or whatever.”

How much Guinness can he get through on a good night? He grins. “I used to get through a load when I was younger.” How many pints? “I could probably do eight, nine, 10.” He pauses. “Then I’d move on to the vodkas.” He giggles. “I could go through loads. I could go all day drinking, then wake up and go again when I was younger.”

Blimey, you were drinking all that as a professional footballer? He nods. “I always say to people who ask if I have any regrets about playing, I wouldn’t have drunk alcohol.” Did he drink more than most footballers? “No.” He quickly changes his mind. “When I was younger I did. I was a lunatic. When I was at West Ham … elements of my career are a blur. People talk about performances and results at certain times in them games and I just sit and nod my head. I haven’t got a clue what they’re talking about. I don’t remember.”

Would he drink on a Friday night? “No, that would be after a game. Saturday or Sunday. It was a different culture. Crazy. The culture I was in at West Ham was a drinking culture. Football and drinks and nightclubs, that’s the way it was. And that’s the way I lived at that time.”

When he went to Manchester United, he says, he pretty much stopped drinking during the season. But he would make up for it in the off season. “In the summers I’d drink for two weeks. Bang. Just keep drinking.”

He could so easily have destroyed his health and career. Does he look back and think he was lucky? “Yes. I was lucky. I had a natural ability that could get me through that period of my life. But I got to a point where I had to make a decision to be more professional.”

Ferdinand’s boozing confessions are certainly a good example of a life lived less healthily, but Lasarow is keen to get back to DNAFit.

“Have you ever done preventive testing?” he asks me. I tell him I’m not proud of this, but I’m more of the less-you-know-the-better school. Ferdinand says he used to be the same. What changed him? Simple, he says – the loss of his wife and mother to cancer. “I’ve got a young family who have seen more than enough trauma for anyone’s lifetime, and I want to be best placed to help prevent anything like that happening if I can. I want all the information I can get from the DNA kit for myself so hopefully my kids won’t have to see any more trauma earlier than they should.”

DNAFit and Ferdinand began their campaign in Peckham, a deprived district of south-east London where the former footballer grew up on a council estate. “We went into a couple of schools, and all the children said: I’d love my parents to do this.” (You have to be 18 or over to do the test.) I ask Ferdinand if it is affordable, but Lasarow answers on his behalf. “How much do you spend a month at the gym? You might go to the gym and pay your fees for six months but not get the right results because you’re not doing the right things. Of course, there’s a price because it’s a science; there’s a commercial aspect. There’s a small price to pay.” How much? “£99.”

Ferdinand remains a hero in Peckham, where he had a fascinating childhood. As well as the football, he was a promising gymnast and ballet dancer, attending the Central School of Ballet for four years. “I went one day as an adventure, and then I was there four years – two days a week, then three days.” Could he have become a professional dancer? “No. At the end they said my hamstrings are not long enough.” Did it improve him as a footballer? “One hundred per cent yeah. Balance, fluidity in terms of my movement, 100%.”

Ferdinand went to Blackheath Bluecoat, the secondary school attended by Stephen Lawrence, who was murdered in a racist attack at the age of 18. Did he know Lawrence? Yes, he says. He was four years younger than Lawrence, but because he was a big, confident boy he played football with him and his best friend Duwayne Brooks, who was also attacked on that night in Eltham. “It’s mad what happened. When it happened it was like your life just comes to a standstill. I’d always seen knives or people get shot or whatever, but a young boy at school getting stabbed to death … it’s like, fucking hell. When the news came the first question I had was: where was it, where was it? Then we heard it was in Eltham. The first thing all of us were saying was: what the fuck is he doing there, in that area, at that time – it’s a racist area, don’t go there at that time.”

When given the chance, Ferdinand talks touchingly and honestly about his past. But even in these moments, Lasarow is keen to intervene. “Simon, sorry to deflect away from that,” he says. “You were saying you’d promise your partner you’d go for a checkup – if you don’t and, God forbid, you fell ill, the burden on her is increased because the associated costs of being ill would have to be taken take care of … ” I’m not sure how to respond, so I don’t.

Did Lawrence’s murder give Ferdinand a sense of how precarious life could be? “It made me aware that if you get into a problem it could be a big problem. But I was aware of that already. I was used to seeing violence.”

Maybe it was inevitable that Ferdinand would go on to campaign about knife crime, and was vocal about racism in football. (After John Terry allegedly racially abused his football player brother, Anton Ferdinand, on the pitch, Rio stopped talking to Terry, even though they were defensive partners in the England team. Terry was banned for four matches and fined by the FA.) But he says his values, his willingness to speak out, came more from his parents than his experiences. “My mum and dad are really community-driven people.” He still sometimes talks about his mother in the present tense. “That’s probably the reason me and Kate are the way we are with the kids because my mum and dad were doers. They didn’t have to tell me a lot about being part of the fabric of the community and being vocal about things. They did it, and I’ve seen it, and that’s why I am the way I am.”

Ferdinand also campaigned for the UK to remain in Europe. How does he feel about Brexit now? “I don’t know man, she [Theresa May] needs a new deal man.”

Lasarow jumps in. “The great thing about genetics,” he says, “and what we’re doing is it can impact anybody or anyone, anywhere, Brexit or no Brexit.” I look at him, gobsmacked.

“Wow, Avi,” I say, “that is the most random intervention I’ve ever heard.”

Even Ferdinand’s agents can’t help laughing at his attempt to steer the conversation back to DNA. Look, I say, we’ve talked loads about DNA, but an interview with Rio also involves talking to Rio about Rio.

I ask Ferdinand if he would fancy going into politics. “No.” Why not? “It’s a murky world. I’ve got no faith or trust in politicians so to be one – I’d find it difficult.” Has there ever been a politician he has trusted? “I like Gordon Brown. I’ve met him a few times. There was a sincerity about him I really liked.”

“Simon, we’ve got a couple of minutes left,” says his publicist.

Ferdinand was part of an England squad known as the golden generation – supremely gifted individuals who underachieved as a team. How did he feel when he saw a more prosaic England team reach the semi-final of the World Cup last year? “There’s no sour grapes, if that’s what you’re alluding to.” No, I say, I’m just interested that they achieved more with less ability. “It doesn’t matter how good you are. You look at our team, we had probably the best bunch of midfielders in the world at the time – Scholes, Gerrard, Lampard, Beckham, Hargreaves, Carrick etc – but we didn’t have a manager who could find the formation that could fit them in and get the best out of each and every one of them. We played a very rigid 4-4-2 or 4-4-1-1, and that was the most intricate it got after Glenn Hoddle. Then we got beat by teams with not as good players, specially in tournaments. So you’ve got to be coached right, and the players have got to believe in what they’re being coached, which this group of players do.”

“We helped the Egyptian team to get to the World Cup for the first time in 28 years,” Lasarow says proudly. “I’m not saying genetics is everything, it certainly isn’t … ” Egypt lost all three games they played at the 2018 World Cup.

In the past, Ferdinand has said that as a player he prided himself on his iciness. Does he think he has changed since retiring? “I’m still quite an intense person but I’m a lot more open. I had the blinkers on. I didn’t see a lot of things emotionally to do with relationships, with friends or family.” I tell him how refreshing it was to see him weeping openly about Rebecca in the documentary and talking about panic attacks – a good example to all the boys and men who suppress their feelings. “Yes, that’s a big thing that came out of it. Everyone’s had a mental health problem in some shape or form, it’s just identifying it and then hitting it head on and meeting it, but again, it’s a cultural shift.”

I ask Ferdinand what he thinks of himself as now, primarily – a football pundit, entrepreneur or campaigner? “I’ve never been anyone who’s wanted to be pigeon-holed. So, for instance, when I did ballet, all my mates from the estate took the piss. But I wasn’t fazed by stuff like that. I’ve been comfortable in my own skin since I was young so I never really cared about what anyone had to say. That’s why, as a footballer, I was comfortable creating a digital magazine, getting a restaurant, going into different fields.”

You were also one of the few footballers prepared to say what you think. “Well, you’re taught not to, that’s the problem.”

Was he pleased that the England international Raheem Sterling recently talked about the racism he has experienced. “Yes, it’s been hard work for him but he’s hitting the right notes, not only on the pitch … ”

But Lasarow has had enough of the football talk. “My mission today is to make sure you leave with a DNA test,” he tells me. He turns to Ferdinand. “I think you want to wrap up now, don’t you?”