Tonga conforms pretty strictly to the universally agreed characteristics of paradise: breathtaking cerulean sea, coconut trees licked by balmy breezes, rudely fertile land, average temperature a travel agent-warming 28.1C. It's your basic honeymoon dream. So when the BBC asked me to leave my demanding young family and visit the island, I tussled with my conscience for a whole nanosecond before squeaking, "Yup."
I've been making a series called Cooking in the Danger Zone - I've visited war zones and dog farms, I've eaten yak penis with communists and World Food Programme rations with refugees, so I was looking forward to this last trip. But there is, inevitably, trouble in paradise.
Tongans are eating themselves to death. Alongside its neighbour Nauru, Tonga, with 110,000 citizens, has the fattest population on the planet: 92% of all over-30s are overweight or obese. The World Health Organisation is clear that obesity increases the likelihood of heart disease and circulatory problems, many cancers, skin problems, infertility and diabetes. Almost 20% of the adult Tongan population suffers from diabetes and the death rate from nutritional conditions is 10 times that of the UK's. It is putting tremendous strain on the health service and the economy, and the problem is getting worse. I visited Tonga to find out why.
From the moment I arrived, the obsession with food was obvious. As my vast guide, David, drove me across the island, I saw 20 or so huge fires over which young men were spit-roasting sucking pigs - sometimes 10 at a time. Hieronymus Bosch would have loved it. The pigs were to be eaten at church conferences - week-long celebrations during which everyone attends three feasts every day. That is 21 feasts in a week. These were frighteningly sumptuous. Tables groaned with food, with a sucking pig every two metres and no space to park your elbows. Some were double-decked with extra food on a shelf above the main table. After a few speeches, everyone tucked in and when the congregation had eaten their fill, they carted off the leftovers in carrier bags.
Overeating isn't the only cause of obesity. The type of food is also to blame - Tongans eat a vast amount of fat. Although they adore sucking pig, it is expensive and usually saved for best. Corned beef is a more everyday staple, and it contains double the fat of that on sale in the UK. Tonga's most popular cut of meat is the disconcertingly named "lamb flap": lamb belly containing up to 50% fat.
In addition, Tongans are huge carb fans, consuming the root vegetable taro, sweet potatoes or yam with every meal. But bad food is available the world over. What about the Tongan lifestyle? From my sweepingly empirical viewpoint, Tongans seem very different from the British: they aren't aspirational in a worldly sense. In fact, many don't seem keen to do much at all, apart from cooking. But Tongans don't appear lazy - just ... unmaterialistic. After all, what good is a flash set of wheels on an island with few roads? And with so much natural beauty at your disposal, a posh house seems like gilding the lily.
In a spiritual sense, however, Tongans are highly aspirational: life revolves around the church and family is enormously important. Lots of family: 10 is a common number of offspring.
There isn't the same kind of stigma attached to being fat either. Tongans, like other South Sea islanders, revere large bodies, though they are beginning to admit that the western ideal is more desirable, at least in health terms.
Fishing and farming used to keep Tongans active but fish stocks are low and the seas crowded with foreign trawlers, so few bother to venture out; and farming seems to be a dying art (the only farmer I met did it primarily as a hobby).
The only people I found exercising with any great application was a walking group based at a hospital and a Boxercise class run by Fane, a Tongan princess.
The idea of genetic predisposition crops up a lot when discussing Tonga. The "thrifty gene" is a theory that has been knocking around since the 60s: by a process of natural selection, Pacific islanders have developed the ability to store fat more efficiently to get them through times of starvation and hardship. These days, starvation isn't an issue, but no one appears to have told the thrifty gene, which carries on doing its remarkably effective job of transforming food into body fat. Even with exercise to shift it, Tongans face an uphill struggle.
It looks as though Tongans are going to need to change their entire lifestyle if they want to avoid the early onset of problems associated with obesity. But the idea that they will start rushing to the gym would be a fantasy. And how do you lower the rate of consumption when it is so deeply ingrained in the culture and indulged by the church? The country is aware of the need for change and even has an obesity prevention action plan called Project Ma'alahi, though it seems slow to achieve anything. More important seems to have been the king of Tonga's achievement - Taufa'ahau Tupou IV reduced his weight from a spectacular 209kg in 1976 to 130kg in 1997.
So are there lessons we can draw from the Pacific experience? Well, yes and no. A sedentary life mixed with a high-saturated fat diet clearly isn't going to do you much good, but the spiritual flipside of low materialistic aspiration might be no bad thing. Luckily, much as we like to blame genetics for our problems, we don't have their thrifty gene.
The thing is, I know what I would do if I lived in Tonga: very little. I might marvel at the beauty and fecundity and maybe procreate a little, but I certainly wouldn't cut down on sucking pig and go Spinning, or whatever it is that people do on those infernal machines. Princess Fane forced me to do five minutes of Boxercise in the heat and I nearly fainted. Tonga will continue to tackle the problems - it can't ignore them - but it is an uphill struggle to make dramatic lifestyle changes when you already live in paradise.
· Cooking in the Danger Zone: Tonga and Fiji is on BBC4 next Tuesday at 8.30pm, BBC4. Stefan Gates is the author of Gastronaut: thegastronaut.com