‘I'm a healthy GP – but I was shocked by the effect three slices of pizza could have’

At his son’s birthday party last year, Dr Rangan Chatterjee managed to eat just three slices of pizza among all the chaotic fun. He was wearing a continuous glucose monitor (CGM) at the time, so he held his phone over the monitor to track his blood ­glucose levels, also called blood sugar.

He is an NHS doctor with 20 years’ experience, but what happened next shocked him. The reading shot up after 20 minutes and then kept going.

“I was watching it go up and up, until it hit the highest my blood sugar has ever been: 12.5-13mmol/L. I’d never seen anything like it,” says the author and broadcaster.

To put the reading in context, for most people without diabetes, normal blood sugar levels are between 4-6mmol/L before meals, and less than 8mmol/L two hours after eating. ­Chatterjee’s response put him in the diabetic category.

Despite the initial shock, as a one-off deviation from his usual diet, Chatterjee decided it was nothing to worry about. But it made him think about patients of his who might regularly eat a whole pizza. If they could see the real-time effect of what sustained spiking of their blood glucose does, might they think before they eat?

The impact of regular glucose spikes on disrupting normal ­metabolic dysfunction has been on Chatterjee’s radar for at least 10 years. But it is only in recent years that CGMs have allowed people to see real-time data. For type 1 diabetics, who no longer have a working pancreas to help them manage their blood sugar levels after meals, it’s a real-time indication of how much insulin they need.

But for people who have not yet been diagnosed with a disease, are the devices useful? Currently, the leading maker of CGMs, Abbott, says that the FreeStyle Libre portfolio is for people with diabetes. However, Abbott’s sensing technology does have the potential for people without diabetes and that’s why they’re developing a line of consumer biowearables under the name Lingo that will track key biomarkers like glucose, ketones and lactate.

The idea of how individual our metabolisms are has been highlighted by the likes of the Zoe Project, spearheaded by Prof Tim Spector, which has shown how glucose responses vary from person to person. The reason why isn’t understood yet, but it is thought to be a combination of genetics, evolutionary heritage and gut microbiome.

On social media, the scientist Jessie Inchauspé, aka the Glucose Goddess, helps people to “hack” their ­metabolism, by showing how to ­flatten their blood glucose spikes with a shot of apple cider vinegar before a meal, and a brisk walk after.

The potential of CGMs to alter the trajectory of those heading towards type 2 diabetes is potent. It’s also unlikely to be offered on the NHS any time soon, which Chatterjee is acutely aware of. “One of my biggest frustrations as a doctor is we practise reactive rather than preventative medicine.”

In the UK, more than 40 per cent of people have pre-diabetes or type 2 ­diabetes. At the moment, the standard procedure on the NHS for assessing metabolic health is a HbA1c level test, which gives an indication of the three months average of your blood sugars.

“If you are 6.5 or above, we say you have type 2 diabetes. If you are 6-6.5, then you are what we call pre-­diabetic, and if you are 5.9  or 5.8, which is most people in the UK, you will have that reported as normal. But it’s not ­normal,” says Chatterjee. “While it’s not pre-diabetes or diabetes, it’s ­certainly not optimal.”

In the US, 88 per cent of the population have a degree of metabolic dysfunction, a result of a standard diet that is full of glucose-spiking processed foods. And we’re not far behind.

“We currently think one in three UK adults display some form of metabolic dysfunction,” says Chatterjee. “That underpins all the chronic diseases that people are worried about: obesity, heart disease, stroke, ­dementia, cancer, fatty liver.

With all of these conditions, while seemingly separate at the point of diagnosis, ­metabolic dysfunction and inability to process and manage energy efficiently is one of the root cause drivers.”

Prevention is clearly better than cure. And so Chatterjee has signed up as an advisor to Levels, an app set to launch this summer that provides real-time feedback on how diet and lifestyle affect metabolic health by leveraging data from biosensors, such as CGMs.

Chatterjee believes in making good health accessible to everyone, so he thought long and hard before collaborating with a private company. Noting that innovation often starts with private tech companies, he hopes that by being involved, he can show the NHS that this is a technology it should be investing in.

Where CGMs can be powerful, he believes, is in helping us make better choices. “It’s going to help us in the short term by giving people more stable blood sugar, which means they will have more energy. It can also help some people with mood, as if you can stabilise your blood sugar, you don’t feel as much anxiety.”

Chatterjee adds that: “A pleasing side effect for many people is that when they establish their blood sugars, some of the excess weight about their tummy starts to fall off. But I wouldn’t say that’s the primary goal. You find your blood ­pressure will start to come down and your HbA1c will have come down.”

Over the longer term, users should be able to reduce their risk of becoming ill. “Regular excessive blood sugar spikes can lead to faster ageing and blood vessel damage,” Chatterjee observes. And type 2 diabetes can be reversed with the right measures.

Chatterjee is talking over Zoom from his podcast studio in Manchester; ­Spector and Inchauspé have both been recent guests on Feel Better, Live More. His passion makes it feel like we’re in the same room. However, his ­enthusiasm for CGMs isn’t analogous to his views on health tracking in general.

“I’m actually not as pro-tracker as many people. I have real concerns over how much tracking is being used.”

Chatterjee wore an Oura smart ring for two months. He comments, “I learnt some key things, such as, if I eat within two hours of going to bed, the quality of my sleep is lower; if I have half a glass of red wine in the evening, my REM sleep drops dramatically. But I think many people are becoming obsessed with health metrics and requiring a device to tell them how they feel.”

He has seen how dependent the ­benefits of health tracking are on what type of personality you are from that most old school of health tracker: the blood pressure monitor.

“Many patients over the years have asked if they should get a home monitoring cuff from the pharmacy, and I’ve noticed that maybe half of the patients said it was a good thing – they checked it two or three times a week and it kept them motivated. But the other half would be checking five times a day and they’d get anxious as soon as it was high and leave messages for me to call them back. It was putting their blood pressure up!”

As a result, Chatterjee cautions that for some, CGMs may become another thing to be obsessed by.

“We should not be demonising blood sugar spikes,” he says. “They’re normal. The problem is when these spikes are high and they’re chronic, happening several times a day, every day.”

He wouldn’t advise anyone with a history of eating disorders to use a CGM. But, as we face a tidal wave of obesity in the UK, he concedes that CGMs offer potential insights that are impossible to get any other way.

“In the UK, we spend around £5.1 billion a year on the treatment of obesity and type 2 diabetes – more than we spend on police, fire service and the judicial system combined,” says Chatterjee.

His enthusiasm comes with a caveat. How useful the information from a CGM is depends on who you are, and your wider lifestyle. If you’re thinking that any sensible person doesn’t need to wear a CGM to know that a diet of refined carbs isn’t going to be a net ­positive, then there are more subtle insights to be drawn from their use.

Frequently, what we think are healthy habits are actually spiking our sugars. For Chatterjee, the more illuminating lessons were about the healthy food habits that were a staple part of his diet.

“Having written numerous books telling us all how to eat more healthily, I am ­committed to walking the walk as well,” he says.

But when he first wore a monitor two years ago, a year before the pizza party, it made him rethink some of his “healthy” staples. Sweet ­potatoes were the first casualty. The wedges he enjoyed at family ­dinners four times a week were ­pushing his blood sugar far too high.

“I’ve got a hearty appetite, but as a result I can overeat healthy food. As someone in an Indian family, I grew up eating white rice. I’ve learnt that quantity really matters. Before, a third of my plate might have been white rice alongside a fish curry perhaps.”

With his glucose levels rising significantly, he experimented with halving that. “A small amount of white rice and my blood sugar is stable. So again it’s helped me to be mindful of quantity.”

There were other insights that Chatterjee acted upon which have made his energy levels and sleep more stable. “I learnt that if I haven’t slept well I can have the same breakfast and my blood sugar will be higher. So sleep really impacts our metabolic health,” he says.

Understanding his own spikes means that he now leans less on caffeine to get himself over energy dips. “A lot of the time, fatigue is because we’ve had a blood sugar spike and then a dip two or three hours later.”

Of course, blood sugar is only one marker of health, and Chatterjee points out that it can easily be gamed when looked at in isolation. “You can have butter and bacon three times a day and have the most beautiful blood sugar line, but I’m not convinced that is good for your long-term health.”

His goal is not for people to wear them 52 weeks a year. Chatterjee only wears a CGM for a two-week spell every three months, using it as a tool to tune back into his body.

“Even with the insights I have, I’m just as susceptible to temptation,” he explains. “This year has been incredibly stressful. My elderly mum has been in poor health this year, so there’s been this added stress on my life, as well as being a father to two young kids. And stress drives up your blood sugar.”

Although, he emphasises, he doesn’t wear a CGM to beat himself up about his choices, but rather to empower himself. “When you use a CGM, you start to see patterns more. You realise, ‘That’s why I’m a bit moody or I can’t concentrate now’. With that you start to naturally make better choices.”

Still, Chatterjee’s wife is yet to try one out. And he doesn’t want to be constantly scanning a CGM in front of his kids. “I don’t want them to grow up thinking you have to obsess over everything you put in your mouth.”

There is also a prohibitive cost ­element currently. For Levels, when it launches this summer, an annual membership and 28-day supply of CGM sensors will cost £334. ­Meanwhile the Zoe Project costs £24.99 per month for a 12-month membership, plus £299.99 for testing.

Chatterjee invites everyone to visit Levels’ free blog, where users can share their tracking insights. His hope is that those who cannot yet access CGMs will pick up tips from those who have.

You don’t need to wear a CGM to start experimenting with managing your levels. A few years ago one of Chatterjee’s patients, a man in his ­forties, was experiencing vision issues. He couldn’t see his computer screen, he would frequently have visual distortion while out walking.

Chatterjee ran tests but then picked up on the fact his patient regularly had two bananas every morning at ­breakfast, thinking it was a healthy choice. After telling him to cut out all bananas, the problem vanished.

“I’m convinced that had that person been wearing a CGM, they would have seen that when they had bananas their personal glucose response took them into a diabetic range.”

With time, he hopes the cost of CGMs will come down and anticipates that in the future they will be freely available on the NHS.

From the number of messages he gets on Instagram about the topic, he knows that there is an appetite already for this technology.

“People know that society is sick. They’re seeing it all around them and they’re feeling it themselves. So many people feel stressed, burnt out and tired, and of course blood sugar isn’t going to fix everything, but it’s remarkable how stabilising your blood sugar can impact your stress, mood, energy, the way you interact with other ­people. It’s such a key marker.”