The lawyers who took on the big US tobacco companies, and won, have now set their sights on the food industry. Newsnight's science editor, Susan Watts, asks one of them why he has chosen this particular fight.

Don Barrett likes his opponents powerful, and rich. He is the lawyer whose decade-long battle to force the tobacco companies to admit they knew cigarettes were addictive and pay the medical costs of victims was depicted in the film The Insider.

He and his colleagues eventually forced a settlement that cost the industry more than $200bn (£124bn). The lawsuits made Mr Barrett a very wealthy man. But he says it is not the potential for another big pay-out that is now making him target "big food".

Image caption Don Barrett's battle against Big Tobacco was depicted in the Russell Crowe film The Insider

"I'm 68 years old, frankly I don't need the cash, the law's been good to me," he explains. "This is my job, but here we have an opportunity to really help people. We're not saying the food industry is the same as the tobacco industry that kills 500,000 Americans a year, but we are saying there is an epidemic of obesity that is affecting the overall health of the American people."

Mr Barrett is one of more than a dozen lawyers who has filed cases against some of the US food industry's biggest players.

They are not the first lawsuits to target food manufacturers. For nearly a decade, US lawyers have pursued a variety of approaches to try to persuade fast food chains to produce healthier, more nutritious food, but these are being seen as some of the most aggressive, despite the simplicity of their approach.

Mr Barrett's case against Big Food is that companies are misrepresenting their products, promoting them as "natural" or "healthy", when in fact, he says, they are no such thing.

The American people assume that if a product is legal to sell, then these people are telling the truth about this product... that's what they thought about cigarettes Don Barrett

His mission is to make them stick to the letter of existing laws which, he says, regulators have been too weak to enforce. He says that the Food and Drug Administration (FDA), which oversees food safety in the US, has merely been writing warning letters, which he thinks will not be enough.

Taking pride of place on the wall of Mr Barrett's office in Lexington, Mississippi is a replica of the flag carried by the Civil War-era 11th Mississippi infantry regiment. Mr Barrett says that like most Southerners he has a soft spot for his ancestors, who "fought so bravely, against overwhelming numbers and resources, defending what they thought was right".

What he himself is fighting for, he says, is people's freedom to make a choice.

"Nobody's trying to tell the American people what they have to eat or what they cannot eat, the American people can make those decisions for themselves. It's all about free choice. To have free choice you have to have accurate information. That means Big Food, the food companies, have to start telling the truth about what's in their product. The law requires it."

He does see similarities with the tobacco lawsuits. "One parallel is that the American people assume that if a product is legal to sell, then these people are telling the truth about this product. If it's legal to sell, it must be ok, otherwise the government would have done something about it. And that's what they thought about cigarettes."

Part of what fires him has been rocketing rates of obesity in young Americans. Though the upward trend is slowing, around two thirds of Americans over the age of 20 are now obese or overweight, according to the US Centers for Disease Control (CDC).

Image caption Around two thirds of Americans over the age of 20 are now obese or overweight

Hidden sugars in processed food, he says, are part of that problem, and mis-labelling is key. He cites one example, yoghurt from the food company, Chobani Inc, which lists "evaporated cane juice" as an ingredient.

"If you're the mother of a diabetic child or the mother of a child that's obese, labels matter. You look for sugar you don't want, and there's none there. What they do have is 'evaporated cane juice'. That sounds sort of vague, and somehow healthy, and natural.

"Evaporated cane juice, if you live in southern Louisiana or in Cuba, you understand what that is, that's sugar... The laws have been there for ever. And they're very clear. You cannot call product by a euphemism."

The company told Newsnight: "Chobani has built our business on being authentic and transparent, and we fully stand behind our products and are always listening to our consumers to make our products better."

Mr Barrett cites another example, foods whose labels suggest they should be kept in the fridge once opened, thus giving the impression that they contain no preservative, and are fresher than they actually are.

If Mr Barrett succeeds in his cases, the industry could face substantial costs.

He claims that if the courts deem mislabelled food products illegal to sell, those products become illegal to hold and have no value. If a product is sold without value, the amount it was sold for is the measure of damages, he says.

His lawsuits are class actions, where the class is defined as every person who purchased one of the misbranded products in the previous four years.

"If it cost a dollar and 25 cents, then the customer is entitled to his dollar and 25 cents back," he explains. "And there's a four-year statute of limitations, so the damages in each of these cases is how much have they sold of this misbranded junk in the last four years."

Barrett claims that some 25% of products are misbranded in the US. So the scale of damages in these cases could easily match the many billions of the tobacco suits.

"It could, and will be, billions of dollars in some cases," he says. "One of the potato chip companies that we're suing sells $13bn (£8bn) worth of product a year."

Previous "fat" cases have centred on false advertising claims, rather than mislabelling, which required the plaintiffs to hire experts to prove that labels were "deceptive" to an ordinary consumer, and such deception caused actual damages.

This has proved an expensive and uncertain process, and such cases have tended to settle for small amounts.

Foods in the firing line Don Barret is suing the makers of over 20 products, which include:

Fruit juices

Crisps

Soft drinks

Chocolate

Tinned tomatoes

Canned fruits

Baby food

Tea

Personal injury claims are even more difficult to prove, according to Mr Barrett.

Linking smoking to a specific disease proved hard enough. It was only once US states brought cases based on reclaiming medical costs, that the tobacco companies moved to settle.

Linking any one food stuff to a later medical condition, such as diabetes, would be significantly harder.

So what is the chance that this current round of cases might succeed?

Mr Barrett says that in the past, lawyers have overlooked the crucial FDA labelling regulations: "The false labels themselves are the only proof we need, and proving the damages is simple: it is the sales of the unlawful product within the time period of the statute of limitations - four years."

And as cases move into the discovery stage, they could evolve, just as happened in the tobacco suits when "smoking-gun" documents began to appear, perhaps even showing that the food companies knew more about the impact that their products and advertising on people's health than the general public.

And then there is emerging science linking food and addiction, which suggests that over eating highly-palatable foods that contain sugar, fat and salt could actually change our brains - so that we need more and more of such foods to feel satisfied.

If this science strengthens, then the parallels with the tobacco cases could strengthen too.

For the time being though, Mr Barrett says his approach is enough to change industry practices: "There's one thing that corporate America pays attention to, and that's getting hit in the pocketbook. It's all about profit. And it's only when you affect their profit that you will affect their behaviour, and we intend to do that."