By Fergus Walsh
Medical correspondent, BBC News
If you want to look at obesity trends, then the US is the place to visit.
Because apart from a few Pacific islands, the US is the world leader in obesity.
It has the most obese population in the developed world, and the rate of increase is alarming.
So where to go in the US? You could choose any state. But one stands out more than most.
Mississippi in the Deep South is proud of its hospitality and of being the home of Blues music.
But one thing it is not proud of is being the fattest state in the union.
The figures come from an annual survey by the Trust for America's Health.
Figures probably worse
Three in 10 (30.6%) of adults in Mississippi are obese, more than in any other state.
Many of the poorest residents rely on small convenience stores where everything is pre-packed
Dig a little deeper and the real level of obesity is probably even higher.
The Trust figures are based on a huge phone survey across the US and rely on people owning up to their weight.
More reliable national data comes from the NHANES (National Health and Nutrition Examination Survey), where individuals are actually measured and weighed.
That shows that whereas in 1994, 22.9% of American adults were obese, it rose to 32.2% in 2004 and 34.3% in 2006.
Now if that's the average across America, it means the figure in Mississippi is probably far higher.
Some estimates suggest that by 2015 half the adult population in Mississippi will be obese.
So how does one state get to be the fattest in America? There are many factors.
The Trust for America's Health survey found that adults in Mississippi are the least physically active of any state.
The climate in Mississippi doesn't help according to the locals: hot, humid conditions for most of the year can make outdoor exercise unpleasant.
The overwhelming feeling I had in Mississippi was that this is a place where - for too many people - food is about convenience and quantity more than fresh ingredients and quality
I visited there in December when the weather was mild, but that still wasn't enough to attract joggers onto the streets.
Poverty is a key factor.
Many obesity studies have shown that, in developed countries, the less educated you are, the more likely you are to become obese.
That is partly to do with food choices.
In the US the relative price of fresh fruit and vegetables has risen dramatically in the past 20 years, while the price of high calorie, high fat foods has fallen.
Mississippi does have supermarkets awash with healthy products, but these can be as much 40m (64km) apart.
That means many of the poorest residents rely on small convenience stores where everything is pre-packed.
I bought a doughnut from a gas station for 50 cents - about 25p.
That one doughnut contained 65% of my daily recommended allowance of saturated fat - much higher than you'd find in most UK snacks.
In restaurants it was often hard to find food that didn't have cheese on top.
The portions are huge and much of the food is deep fried. What about home-cooked food?
Interestingly, Mississippi has some of the richest, most fertile soil in the United States.
Yet I was told few people grow their own vegetables any more.
Mississippi also has one of the highest and poorest black populations in the US.
There may be genetic factors that put African Americans at greater risk of obesity. But social and living conditions are crucial.
The town of Belzoni, in the Mississippi Delta, calls itself the catfish capital of the world.
It's a quiet poor town with a large black population.
The local clinic is run by father and son doctors Mack and Carlton Gorton. Like many of his staff Dr Mack needs to lose a lot of weight.
A doctor in the town for more than 30 years, he told me how his patients are getting heavier each year, and obesity is affecting younger and younger children.
They now have some as young as 10 with obesity-induced type-2 diabetes.
Scared of surgery
I went to the home of Shillese Hazelwood, a patient at the clinic.
She weighs nearly 500 pounds (220 kg).
She is so disabled by obesity that she can't work.
Shillese has been offered a stomach bypass but she is scared of the surgery.
She couldn't explain why her weight had got to this extreme point, but suggested to me that being born premature may have been a factor.
She takes a range of tablets for diabetes, high blood pressure and other ailments.
Shillese lives with her brother and sister who are also obese and unable to work.
The cost of treating obesity-related health problems is soaring.
There are predictions that the state health-care budget could be bankrupted by obesity in a decade or so unless urgent preventative action is taken.
There are some positive steps being taken. Some schools in the Mississippi Delta are running obesity prevention programmes.
Children are encouraged to eat breakfast so they stay more alert at school.
Deep fat fryers are being ripped out of the canteens, and healthy choices being included on the menu.
High calorie soft drinks have been banned from vending machines. More physical activity is on the curriculum.
Incredibly, some American schools have abolished recess - break-time - where children usually run around outside and play. Now it is being re-introduced in the Delta region.
But the overwhelming feeling I had in Mississippi was that this is a place where - for too many people - food is about convenience and quantity more than fresh ingredients and quality.
If the US and Mississippi are to do anything about their obesity problem then they will have to do two things - tackle their addiction to fast food and get out of their cars and walk.
Neither seems remotely likely, and as a result most Americans will continue to get fatter.