The final episode of Michael Mosley's Channel 4 weight loss show airs tonight. From how to burn fat to making mushroom pizza, it's been quite the learning curve

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Let's be honest, diets with screamer headlines promising to ‘drop 10 pounds in 10 days!’, or ‘get a flat tummy in five!’ sound attractive but we all know a marketing ploy when we see one and are more likely to grab another kettle chip than sign up. So how is Channel 4’s new hit series Lose a Stone in 21 Days with Michael Mosley, of which the final episode airs tonight, different?

The three-part show which put five volunteers o a three-week rapid weight loss diet, focuses on losing 'corona' pounds. It comes after reports that two-thirds of the population put on weight in lockdown. In July the government launched a major new obesity strategy  urging UK adults to lose weight in order to reduce the risk of serious illness including COVID 19. It includes an NHS app with a 12-week weight loss programme.

We know that obesity significantly increases the chance of becoming seriously ill from coronavirus, as well as being a risk factor for a host of other life-limiting diseases such as heart disease and diabetes. Shedding the extra pounds has become a potentially life-saving intervention.

The doctor behind the show Michael Mosley is the creator of The Fast Diet 5:2 diet  and The Fast 800 online plan, says in episode one of the three-part series, “It’s not about looking good in a swimsuit, it’s about fighting disease.” And with the chances of becoming seriously ill with COVID increasing with your BMI, obesity has become an even more pressing health issue.

Dr. Mosley’s intermittent fasting-style diet Fast 800  plans, which involve both fast and slower weight loss routes and health maintenance, are based on the Mediterranean  way of eating and claim to have helped hundreds of people shed pounds quickly, safely and sustainably. It is based on several studies  of an 800 calorie diet to achieve major weight loss and remission from type 2 diabetes. In this show, he puts five volunteers on his 'very fast' very low carb weight loss plan of 800 calories a day, supervised by himself and his GP wife Dr. Clare Bailey.

It's not without controversy though. The first episode caused a Twitter backlash with some arguing that such rapid weight loss was triggering for people with eating disorders. Eating disorder charity Beat announced that it was extending the hours of its helpline to 11pm to coincide with the airing of the show. Meanwhile, Dr Mosley told ITV's This Morning that the chosen method was based on methodology on several recent “big randomised controlled trials”. He also points out in the programme that the NHS is beginning to trial rapid weight loss diets "with suitable patients".

The programme’s volunteers put their lockdown weight gain down to factors we can all relate to: increased snacking while bored, isolation, picking from kids’ plates, moving back in with mum and dad to delicious home-cooked meals as well as extra drinking to manage stress. While their weight, cholesterol levels, BMI, and blood sugar scores were worrying at the start, Dr. Mosley assured them that change was possible. “Three weeks on the 800 calorie diet switches you from burning sugar to burning fat and is a really rapid way to change things and within a short time you stop getting hungry,” he encouraged. As a type 2 diabetic himself eight years ago, he’s been there.

After three weeks Dr. Mosley will measure how losing weight by eating healthy food and taking moderate exercise has improved their immunity.

This is what we have learned so far (and if you are planning to go on a diet, please consult your doctor first).

We spent an EXTRA £19 million on biscuits in lockdown

It’s no surprise that two-thirds of us admitted to piling on the pounds during lockdown if our biscuit consumption is anything to go by. Dr. Mosely had this and other sobering statistics to share. Surveys showed that in the first five weeks of lockdown, 16 per cent of us had already put on an extra five pounds. And in the four weeks leading up to lockdown, sales of crisps and snacks shot up by 33 per cent. “In crisis, we reach for all the wrong foods,” says Dr Mosley.

It’s not just food. Half a bottle of wine a night piles on an extra empty 400 calories, adds Dr. Mosley, not to mention the fact that we all make worse food choices when we’ve had a drink.

Your metabolic age might be older than you think

Your metabolic age gives a picture of how old you are on this inside and is a comparison of your basal metabolic rate or BMR, the rate at which your body burns calories compared to others in your age group. The volunteers, stepped on a metabolic weighing scale to find their BMR (you can buy similar ones such as the Tanita RD-953S Connect Body Composition Monitor Scale £175 ) and discovered they had a metabolic age up to 15 years older than their chronological age. To gain a fuller picture of their health, Dr. Mosely also gave them a blood test and a breath test as well as measuring their waist relative to their height, because…

Your waist should measure no more than half your height

Anything outside of that range and it means you have too much belly fat or visceral fat, the ‘red flag’ fat around the internal organs which puts you at risk of certain cancers, heart disease and type 2 diabetes, notes Dr. Mosley “all of which will knock years off your life.”

We underestimate our waist size

“We’re one of the fattest nations in Europe but we’re also in denial,” says Dr. Mosley as he took to the streets to ask shoppers to estimate their waist size before giving them a tape measure to find out what it was in reality. Most people underestimated theirs by around ten inches. A survey of 2,000 people showed this was not unusual.  “Only one in ten people who are obese actually realise it,” he says.

First rule of dieting – get it out of the house

We don’t need reminding that if food is in sight we’re more likely to graze. That office tray of donuts doesn’t stay unloved for long. Dr. Mosley instructs his dieters to chuck their nemesis, from biscuits to booze, down the sink, bin it or even stamp on it. (Remembering Miranda from Sex and the City squeezing washing up liquid onto the cake she’d picked at from the bin, putting the bin outside is not a bad idea either).

MORE GLOSS: How to succeed at the 5:2 diet, according to Dr. Michael Mosley

Our bodies are like a hybrid car, they have two different fuel sources

The body has two sources of fuel - sugar and fat - that we can switch between “like a hybrid car,” explains Dr. Mosley. We store 500g of sugar in our bodies for fuel – it lives in our liver and muscles. The average person has 17kg of fat stored in their bodies. That’s true for men and women (women have a higher proportion of body fat) and has been measured by a Dexa body scan.

To lose weight, you need to burn fat not sugar

Flipping the metabolic switch from sugar burning to fat burning is the reason why this low carb, high protein, and relatively high fat 800 calorie intermittent fasting diet is effective. Eating a very low carb diet (a handful of blueberries or strawberries were the only sweet things on the volunteer’s plates) will run down your stores of sugar after two to three days and cause the body turn to burn fat for fuel instead (more specifically convert fat into ketone bodies for fuel) known as ketosis. Like the volunteers, you can measure if you are in ketosis by peeing on a special colour-changing ‘keto stick’.

Mushrooms make surprisingly good pizza

No not pizza topping but an actual low carb pizza suitable for an 800 calorie day. Dr Mosley’s wife GP and recipe creator Dr. Clare Bailey devised a low carb dinner with Portobello mushroom as a base topped with tomato paste, chopped tomatoes, garlic, olive oil mozzarella and fresh basil and grilled. One volunteer declared it delicious.

Putting mushrooms in the sun dramatically increases their vitamin D

If you put your mushies outside or on the windowsill for a couple of hours it can boost their vitamin D content up to 100-fold, says Dr. Bailey. Vitamin D is an essential vitamin for myriad processes in the body including immunity and government advice over lockdown has been for everyone to supplement with vitamin D.

MORE GLOSS: Best vitamin D supplements  

For a diet to succeed it has to have enough protein

“Protein is hugely important when losing weight to preserve muscle mass,” says Dr. Mosley. It’s fat that you want to lose not muscle, especially as muscle tissue burns calories. Some of the volunteers took one of their meals as a meal replacement shake containing 20g protein to ensure they were getting enough.

How much protein does the average person need? Most adults need around 0.75g of protein per kilo of body weight per day (for the average woman, this is 45g, or 55g for men) according to the British Heart Foundation. 

You need to run 35 miles to burn off a pound of fat

Episode Two shone the spotlight on how much to exercise when you're dieting. Michael explains that you'd need to run 35 miles in order to burn off a pound of fat so exercise is not actually a great way to lose weight (as we all know abs are made in the kitchen ). However, it is a good way to boost your metabolism especially as half of us are doing less exercise than we were pre-lockdown lives.

So just how much exercise do you need to do a week? "Two and a half hours of moderate exercise a week is recommended is by the NHS or 75 minutes of vigorous exercise," explains Michael.

We lose 5% muscle mass every decade so weight training is important

The older we get the more we lose muscle mass. From age 30, we lose around five per cent of our muscle mass every decade. Unless, that is, we do resistance exercises such as weights or press-ups, anything that pushes against a weight or isometric exercises such as yoga that use your own body weight as resistance.

Resistance exercise is key to maintaining muscle mass and in any weight loss programme maintaining muscle mass is key. Dr Mosley urges his volunteers add this to their weight loss, kicking off with a HIIT training session with his son, working major muscles of the body, 30 seconds on, 30 off.

How good your balance is, may be an indicator of how long you'll live

Our balance declines with age and having good balance is a sign of youthfulness. How long you can stand on one leg with your eyes closed is a good predictor of life expectancy, Dr Mosley explains. If you're 50+ and can stand on one leg for eight seconds you're doing well. In your 40s you should be able to clock up 13 seconds. At 60-plus four seconds is good going.

Losing weight can help you stop snoring

An irritating side effect of being overweight is snoring and sleep apnoea, a condition where you stop momentarily stop breathing in your sleep, causing you to grunt and splutter (and wake up your bedmate). A staggering 41 per cent of adults snore; it's more common for men and more common as you get older.

Dr Mosley himself was a big snorer, but once he lost weight he became a silent sleeper - much to the relief of his wife Clare. As well as age, weight and genetics, neck size also plays a key part in if you're a snorer; necks over 16 inches for women or over 17 for men mean you're almost certainly a snorer.

Lose a Stone in 21 Days is on Channel 4 tonight at 9pm.