Crossing your legs is not going to make varicose veins worse. The appendix does have a raison d'etre: it's a reservoir for "good" bacteria. Potatoes and pasta will spike your blood sugar something terrible but stick them in the fridge overnight, reheat them and they basically become superfoods. (In my head this definitely extends to reheating KFC fries.)

I know these things to be true because Michael Mosley, broadcaster, author and oracle, says it is so. The man is delighted by science, driven by it. He has made himself its conduit. "I see myself as an enzyme," he tells me. "An accelerant. A catalyst."

For 30 years – after bailing out of banking, then medical school, to join the BBC – the Brit has been boiling down the best of medical science into authoritative, snackable content.

He likes to play guinea pig: he has swallowed tapeworm eggs for the cameras, taken truth serum and hallucinogenics, watched an agar model of his own body be overtaken by superbugs. He's responsible for dozens of documentaries and a clutch of best-selling books; screeds of interviews given and columns written.

Net effect: an awful lot of good.

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His 1995 doco Ulcer Wars covered a finding about stomach ulcers that would go on to win the Nobel Prize. At the time it was thought the condition was caused by stress, and it was often "treated" by removing part of the stomach. But Australian scientists put the blame squarely on a bacterium - and found a cure could be as simple as a course of antibiotics.
The show prompted a sea change in treatment.

Now, Mosley reckons he's topped that. He was diagnosed with the Type 2 form of diabetes six years ago, back when it was considered an unstoppable, Titanic sort of disease: once on the collision course, patients faced a cascade of devastating health problems - and a tragic ending.

Front of Mosley's mind was his late father; diagnosed at about the same age, dead at 72. Mosley threw himself into research and then into a particular sort of crash diet that hinged on intermittent fasting. Stunningly, his condition reversed. He'd turned the Titanic.

Then he turned it into great telly, of course, and followed up with two books – The Fast Diet and The 8-Week Blood Sugar Diet – that sold their socks off and that some doctors now prescribe to their patients.

"I think that genuinely has changed the world of Type 2 diabetes and pre-diabetes," he tells me. "I hope so."

Hold that thought.

We met a few months ago when Mosley was in Auckland to promote a new book, The Clever Guts Diet, which focuses on the wonders of the microbiome – the bacteria in our guts. Now, his myth-busting series Trust Me, I'm a Doctor is now about to land on BBC Earth.

I have 50 minutes. I have a list of really great questions. And I have a migraine that has dropped a shimmering curtain across my eyes.

So I ditch my list, and listen.
 
The accent is posh – he was born in Kolkata, educated at Oxford; sounds like Hugh Fearnley-Whittingstall. Thirty years of telly have drilled home the habit of never saying "um". "Aaaaah," he'll say, on the odd occasion he's asked something he actually has to think about. "Errrr…"

When he's really hitting his stride, he'll bust out a rolled r, Kim Hill-style. In his writing, on TV, in person, he exudes confidence and quiet faith.

"Yes," he agrees. "And I endlessly question it at the same time."

As it turns out, the oracle is a fretter, a double-triple-checker. He lies awake at night wondering if he's got things right.

"I pretend to be quite chilled, but I'm not," he says. "If I've written an article I worry about whether it was accurate. If somebody contacts me and says, 'I [followed your advice] and I became quite ill,' I worry about that."

He was in a "real state of terror", he says, while writing The Fast Diet.

"It was very controversial at the time and there were limited studies, and I was saying something which frankly very few people had said before."

Put yourself in the woo-woo box and you'll never get out, I say.

"Absolutely."

A couple of years later The 8-Week Blood Sugar Diet was about to hit shelves and he was barely sleeping. This book was more specifically aimed at people facing diabetes. The big study he hung it off was only halfway done; at the 11th hour he took its architect, Professor Roy Taylor, out for a drink. "I said, 'Tell me. Has it been an utter fiasco disaster, am I going to have to pulp every edition?' He said, 'No, it's been brilliant.'"

Breathe out.

He says he's never been successfully sued, or had to retract anything of significance.
Yet some of what Mosley says – the science he conveys - is hard to hear. He worries about that, too.

He's fairly militant on rising rates of Caesarean section, for example. He tells me we're approaching bulldog status: the dogs have been bred in such a way that they're now unable to give birth vaginally.

"[Humans] are actually moving to that point, where we are delivering such fat babies that they have to be delivered by C-section."

Further, in Clever Guts, he sets out how science is linking C-sections to higher lifetime risks of allergies, Type 1 diabetes, asthma, eczema and obesity. The problem, it's suggested, is that baby's microbiome gets off to a bad start, because baby doesn't get a gulp of the mother's bacteria on the way out.

I've had a C-section, I say, and my boy has asthma and eczema. I felt that like a body blow.

"Indeed … I wonder sometimes when I write things, whether I should write things."
He always comes down on: yes. Because, he argues, he doesn't just deliver bad news – he tells us how to do something about it.

Mums can breastfeed to build up baby's microbiome, for example. Or they might request that a vaginal swab, swarming with lovely bacteria, be wiped over baby soon after birth. When they're wasted on morphine due to baby having just been hauled out of a wound in their abdomen, I think to myself. Also, not all mums can breastfeed.

I agree with him: knowledge is power. But if you can't act on it, well then it just makes you feel shitty.

This is one area where Mosley seems to have a certain cognitive dissonance. He believes his diets and fasts and myriad tips – short sharp bursts of exercise, sleep more, cut down on stress, et cetera - are widely accessible.

He volunteers: "You've got this idea that it's really just a middle class thing," then counters with the experiences of his wife and professional sidekick, Clare Bailey. She works as a GP in a deprived area, yet many of her patients see the sense in his recommendations, he says, and successfully put them into practice.

I don't push him on this. I should have, because that's … not good evidence.

According to Mosley the ideal diet would be sans sugar, simple carbs, sweeteners and all processed foods. Read: the cheap stuff. What to eat instead? A Mediterranean diet of fresh non-starchy veg, nuts, oily fish, high-quality olive oil, eggs, dark chocolate, red wine. Top it up with fermented foods – kefir, kombucha, yoghurt, kimchi. Add apple cider vinegar and coconut oil to the shopping list, too.

Picture the receipts and then picture a family trying to stretch $80 for food across a week. Where the parents work shifts, come home knackered and stressed, and cook dinner with a hungry child hanging off them.

Even if olive oil and salmon rained down like manna, the planning and preparation – not to mention sheer bloody willpower - involved in a diet overhaul is significant. It's beyond me right now, and I have resources and time, fancy oils in the pantry and a garden full of kale.

Mosley urges me to do an exclusion diet to try to get rid of the migraines. Per Clever Guts that would mean weeks of no gluten, no sugar or processed stuff, minimal dairy, no pulses.

"You sound unconvinced," he says, when I demur. I'm convinced that it's probably a good thing to do, I say, but it just seems a bit daunting.

"No, quite. Priorities."

The thing is, of course, it's the people who would benefit most from Mosley's advice who are least able to follow it. Obesity and type 2 diabetes are rampant in New Zealand – a quarter of a million Kiwis have diabetes, and one in four of us are headed that way - and if you look at the graphs, diagnosis rates rise along with deprivation. It's the same story for anxiety and depression, and heart disease, afflictions known to be related to weight and diet.

That night I scan the room at a lecture and book signing Mosley's holding at the Ellerslie Events Centre. I see manicures, warm coats, newish cars. People who are able to pay for babysitters, for petrol.

It's clear that putting the onus on the individual can only change things so far. And on this Mosley's absolutely with me. Outdated advice and public health messaging makes him truly, visibly angry.

"High on my list of really stupid messages is 'eat lots of small meals', which is the worst possible advice ever, yet I heard a dietitian giving it the other day. Stupid. Stupid. The idea that you should keep your blood sugars constantly topped up is the world's worst, stupidest advice …

"You say to [overweight] people, 'Eat less and do more exercise.' That's kind of like going along to your tennis coach and they say, 'Hit the ball very hard and earn lots of points.' It's just futile as a message. It just doesn't bloody work … I just want to slap the people who say it."

I mention the menus of hospitals and rest homes: scones, mashed potato, juice. He sighs.
"It just makes you go bonkers."

Michael Mosley, the science / medical (5:2 diet guru) journalist, pictured at the Glass Goose in Auckland. Photo: Greg Bowker
Michael Mosley, the science / medical (5:2 diet guru) journalist, pictured at the Glass Goose in Auckland. Photo: Greg Bowker
A

nd yet. That thought you've been holding? About the future of diabetes? Some really quite gobsmacking news landed last month, well after our interview.

The United Kingdom's National Health Service is about to start prescribing diabetics a for-the-masses version of Mosley's rapid weight-loss diet. Patients will spend five months on special shakes and soups, dropping their daily calorie intake from up around the 3000 range to the 810-850 bracket. In a trial run by Roy Taylor and funded by Diabetes UK, half of 300 diabetics on the diet went into remission.

"It has been a great week for those of us who have been arguing for years that it is possible to halt the epidemic of type 2 diabetes," Mosley wrote in a Daily Mail column. He added that he hopes this is the start of a revolution. And he wrote about his wife.

He's been concerned for years that in going out on a limb and prescribing diets, rather than medication, to diabetics, Baileywas leaving herself vulnerable. If anything went wrong her actions would be measured against the status quo - not the best new science. Now, Bailey and doctors like her are protected. Again, breathe out.

She provides many of the recipes in Mosley's books; fields the more pragmatic, specific questions on tours; frogmarches him past pastry shops when he wants to stuff himself with buns. She's set up a fermenting station on the bench at home.

She has heard his favourite anecdote about their marriage 84,000 times but still laughs quietly when he rolls it out in public. Here it is: the dean at their medical school looked at the class of 100 students and decreed that statistically, four of them would marry. And so it was. Maths: one. Romance: none.

Mosley's burying the lede. Here's the proposal story, which he doesn't often tell.

After they'd been together a while, Bailey went to work with Save the Children, in the Amazon. Several months in, Mosley was getting twitchy. He decided to go to join her. Couldn't call first – no way of getting in touch – so he flew the long-haul to Lima, then on to Pucallpa, where he hopped on a mail plane stopping in the spot Bailey was meant to be. Imagine our intrepid suitor: exhausted, bleary, hopeful … bugger.

"She wasn't there. She was somewhere up the Amazon. They sort of vaguely pointed - 'that way' – so I hired a guy with a canoe and we spent a few days trundling up the Amazon.

"Anyway, so aaaah, we arrived, and the sun was setting, and I was so pleased to see her I proposed on the spot. On a grassy knoll, up the Amazon."

The pair married in London in 1987. Mosley has said that it's Bailey who taught him about emotional relationships - that he became alienated from his parents when they packed him off to boarding school aged 8.

How did he juggle parenting his own four children with such a consuming career? He held the fort at home for nine months when the kids were young, he says, so that Bailey could finish medical school. And he stepped sideways at the BBC, from directing to executive producing, which cut right back on travel.
"Clare has done the bulk of it, to be honest."

The nest is nearly empty. Their youngest, Kate, is in her late teens. She recently discovered she was gluten-intolerant and, under Dad's guidance, phased it out of her diet.

"Her symptoms had previously been moodiness, bloating, really bad headaches. When she came off gluten, everything went. Her mood improved enormously, no pain, nothing. And occasionally we have accidentally slipped gluten into her diet by getting the wrong sort of soy sauce and immediately it comes back."

He last saw Kate a few days ago when she FaceTimed him from somewhere in Vietnam, or maybe Thailand. She'd been glutened. She was vomiting into a bucket. Paging Dr Dad.
Up next?

When we talked, Mosley was working on a two-part TV series about what happens after death. As in, what happens to the body, and all those bacteria. (After reading Clever Guts I'm betting on something like the Natalie Portman sci-fi Annihilation, in which human bodies dissolve into clouds of alien microbes).

He's made two other documentaries that involved filming a person dying. Took ages, and unbelievably expensive, he says. He says things like that. Journalists, eh?

"[These shows are] always intensely moving, but the biggest pain is that you get these volunteers - you get somebody prepared to be filmed dying - and then you come along with a camera and they live for another six months because they've got a new lease of life." (As I finished writing, Mosley tweeted that work on the series was "sadly somewhat stalled for reasons outside our control. You can imagine the sensitivities.")

He's 61. What will get him in the end? For once, the oracle pauses before answering. He stalls, pulling words from his mouth like gum.

"Iiii… suspect it'll be cancer. I'm reasonably, errrrr, confident it's not going to be heart disease. It might be getting run over by a bus, or … I would love to think it's going to be paragliding, arhhh, but arhhh… I suspect it'll be cancer. Cancer is juuuust, a lottery."
Death of the guinea pig. Will it be televised?

He laughs. Relaxes. His family would get the casting vote, of course.

"I'm quite happy, in my death, to be televised and for [viewers] to watch my body decay, rot … I don't give a damn after I'm dead. I think it'd be quite fun."

Trust Me, I'm A Doctor premieres on BBC Earth, Wednesdays from October 24, 8.30pm, Sky Channel 74