They widen waistlines, lighten wallets and even spread anti-Japanese sentiments. To critics, their yearly appearance is associated with waste and ostentation.

But China's centuries-long love affair with the mooncake is unstoppable. Eaten to celebrate the mid-autumn festival, when friends gather to admire the harvest moon, they have evolved, with the country's embrace of consumerism, to reach new heights of luxury and exoticism.

"It's just like how Americans eat turkey. Nobody knows why we eat them, we just do," said 25-year-old Tang Cong, who works for an internet company in Beijing.

Round or square, the palm-sized pastries – sometimes chewy, sometimes flaky – are decorated with patterns and traditionally filled with pastes such as lotus seed and sometimes salted duck egg yolks. As high in fat and sugar as they are rich in flavour, they are usually eaten in small wedges, accompanied by tea.

Their increasingly esoteric fillings now include ham and rose petal, sea cucumber and peacock. Häagen-Dazs makes ice cream versions; Starbucks offers chocolate varieties. At the Chongqing Mooncake festival, the centrepiece is a 300kg monster.

They have even appeared in non-edible form. Gold shops sell solid discs styled to resemble the pastries. Last autumn, the makers of Angry Birds produced a special edition of the game with golden mooncake slices instead of eggs.

Though mooncakes are rarely eaten by the buyer – they are generally destined as gifts for friends, employees or business contacts – they say a lot about the purchaser.

"Young people tend to lean towards Häagen-Dazs mooncakes; these kinds of stylish mooncake. People who are a little bit older, they're a little bit more sentimental, so they tend to buy more traditional mooncakes, like red bean," said Li Heshui, manager at the Beijing wholesaler Shangpin Zhenghua.

Financial, technology or media companies are more likely to buy modern versions, while construction firms and manufacturers tend to opt for cheaper, traditional varieties, he added.

The pastries can embody not just one's tastes, but even one's political views: last week, as anti-Japanese protests spread through China, a nationalist – or enterprising – baker produced a set of four with slogans on top including: "Bite Little Japan to death!"

But the pastries say as much about the recipient as the donor.

"These mooncakes are for our rich, honourable friends – high-level leaders and rich businesspeople," explained a sales assistant, also surnamed Li, as she sold "Nobility Promise" mooncakes at an upmarket shopping mall in central Beijing ahead of this Sunday's festival.

A box of 10 – about the size of a small coffee table – cost 1,080 yuan (around £100) and included abalone and sea cucumber varieties.

"Those over there are for our ordinary friends," she added, gesturing at individually wrapped ones in the other corner.

Soaring prices have prompted authorities to step in and curb the excesses of the mooncake trade in recent years. Regulations now outlaw unnecessarily lavish packaging and the inclusion of expensive bonus gifts, such as high-priced alcohol, in the boxes.

"It was partly because of corruption, but also it was just a waste of resources," said an official at the Beijing Association of Roasted Foods and Sweets.

Some customers have also grown uneasy at the health implications of the treats, which clock in at around 800 calories apiece. A handful of firms claim to offer versions with lower fat and sugar, somewhat akin to the idea of a healthy Christmas pudding.

According to a Chinese news site, one brand boasts that its milk and papaya-flavoured versions confer a range of aesthetic benefits, including a more youthful appearance and larger breasts.

But there are signs that even with such innovations, mooncakes may have become too popular for their own good.

Aware that clients may be inundated with boxes, many companies now send them coupons instead. Recipients can order mooncakes – or something else entirely, such as French red wine, Chinese tea or Spanish olive oil, said Mr Li.

Tang said younger people rarely bothered exchanging mooncakes with friends these days.

"Now it's just a business thing. This year my boss gave me two or three boxes, but I haven't bought mooncakes for anyone," she said.

"I actually don't really like them."