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When it comes to understanding the challenge facing the nation on obesity, yoghurt is a good place to start.

It's one of the most common items in our shopping basket. We spend more on it than we do on crisps and bacon.

In its normal state - natural full-fat - it's pretty good for you. It can boost your immune system, is good for your bones and is great at satisfying hunger.

The problem is that a great deal of the yoghurt we buy is not the natural stuff. Instead we seem to like the processed products, which are made by partly substituting yoghurt and adding a combination of other ingredients such as gelatine, sugar and flavourings. It tends to be cheaper to produce per calorie, but nowhere near as good for you.

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The Food Foundation campaign group has taken a look at this. In a report earlier this year, the group analysed Muller Corner yoghurts, the brand leader accounting for about 15% of the market.

Muller produces a number of different types, one of which is the crunch corner series of yoghurts. They contain between 21g and 30g of sugar - most of this is from added sugars rather than natural sugars from milk.

For a young child these products can contain almost enough sugar to take them close to their daily recommended sugar intake. For adults they commonly have enough to take them over the halfway mark.

To support sales, Muller Corner heavily invests in advertising. It is the dairy industry's biggest spender - investing over £10m a year in 2015, the Food Foundation report said.

The vast majority went on TV adverts, including during X Factor, which, while watched by many children, is not covered by the ban on junk food advertising, which only applies to programmes aimed solely at children.

Image copyright Science Photo Library Image caption Three-quarters of middle-aged men are overweight or obese

Muller, as you would expect, defends its brands, pointing out it has a range of products, including Mullerlight and Muller Rice, and that it is clear all its products should be consumed as part of a "varied and balanced diet".

But this doesn't wash for campaigners. They want tighter restrictions on the food industry believing the way food is now produced, marketed and promoted is to blame.

Some 58% of advertising spend is on confectionery and convenience food, compared to only 3% on fruit, vegetables and pasta.

Less healthy foods are a three times cheaper source of calories than healthy foods, while promotions cause us to buy 20% more than we would otherwise.

Campaigners call this the obesogenic environment and say it is a major reason why we are not eating the right sort of food.

Nearly two-thirds of the calories we consume are from highly processed foods, many of which are low in fibre and high in fat, sugar or salt, while three-quarters of us do not eat enough fruit and vegetables.

So what can be done? The tax on sugary drinks, announced earlier this year and due to come into force in 2018, was widely welcomed. But it is seen as just a start by the health lobby, which has been buoyed by its success in convincing ministers to take the plunge on the sugar tax - for months they had been suggesting they weren't keen.

Other steps, including a more substantial restriction on advertising, an end to promotions such as buy-one-get-one-free deals and clearer labelling, are now being targeted.

Will they get their way? They certainly have the ear of government and with the obesity strategy expected to be published as soon as the EU vote is out of the way we should find out sooner rather than later.

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