The Men Who Made Us Thin: Can you be fit and fat?
Presenter and Journalist
I visited Brazil where gastric surgery is a huge industry. Watching a gastric bypass in the operating suite is somewhat equivalent to those anti-smoking ads of the 70s and 80s when school kids were shown the amount of tar in their lungs.
If you wanted an ad to put you off highly calorific processed food then it should show the fat around your vital organs. It's revolting and changed my attitude to being overweight.
Of course if you're morbidly obese there are serious health consequences, but for most of us who struggle to lose a few extra pounds the lesson I took from making this programme was to stop focusing on the weight and instead on being fit and happy.
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In my experience people want to be thin partly for cultural reasons - to fit in to the desirable norm.
But these cultural reasons also start to become biological reasons over time - when being thin becomes equated with being more attractive, and this means attracting a mate, this becomes a biological imperative.
One reinforces the other - it's a vicious circle.
Looking back to the post war period, before we even had an industrialised diet industry as such, one American insurance company reclassified the body mass index (BMI) scale.
The decision labelled at least half the US population as overweight when they had previously been categorised as normal.
Arguably this triggered a sense of panic about weight which stays with us to this day.
The series also made me realise how the overweight are doubly discriminated against.
First they are shamed by society, then they are told that when they don't lose weight long term through commercial diet programmes that it is their fault.
It was interesting meeting the people who had created the diets worth literally billions - Danny Abraham with Slim-Fast and Pierre Dukan and learning about Jean Nidetch of WeightWatchers - what they all share is huge charisma.
This is why they become gurus - people want to believe in someone who says: trust me, I will help you lose weight.
I spoke to a lot of scientists for this series and discovered that around 85% of people put the weight back on after five years.
Personally I think people should stop worrying about their weight and focus on being healthy and happy, at any size.
Exercise is often seen as an important tool of weight loss but I was really interested to speak to Dr Terry Wilkin who is conducting a long-term study at Plymouth Hospital.
He explained to me that 75% of the calories we use we burn just by staying still. These calories fuel the metabolic processes which keep our bodies functioning.
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So no matter how much you exercise your calorie burning effects are limited by your metabolism.
Therefore although exercise is fantastic for getting fit it’s not necessarily great for losing weight.
People who say they lose weight through exercise have actually done so because they already have the right mental attitude towards it.
The psychological battle has already been won before they put on those running shoes.
But exercise is undoubtedly good for you. Fit people live longer. Thin people however do not necessarily live longer.
Being underweight can be as serious a health issue as being obese. Being overly thin - ask any recovering anorexic - is not a good place to be.
In the programme I attended a boot camp with two obese women - both named Katie - who proved they were far fitter than me in spite of their weight.
Being beaten was a real lesson - it proved that being fit is more important than what size you are. And losing so easily was even more humiliating than having to wear the boot camp's pink T-shirt!
Both Katies had found that by focusing on fitness rather than weight loss they had lost weight as a by-product.
They had begun to eat more healthily but with fitness always the goal, weight loss had happened anyway: very small changes on a daily basis make a huge difference.
But the key advice which I picked up again and again throughout the making of this series was that it’s important to change your mental attitude.
The key seemed to be not to focus on the weight but on getting fit and whatever you do, don't crash diet or go on a fad diet.
Comments made by writers on the BBC TV blog are their own opinions and not necessarily those of the BBC.