To enter the highlands of Chiapas, in southern Mexico, is to enter a world of vibrant indigenous culture, breathtaking natural beauty, entrenched racism and grinding poverty. It is also to enter the territory of Coca-Cola.

More Coke is consumed per capita in Mexico than in any other country, and some studies suggest the indigenous communities of the highlands, or Los Altos, may be the soft drink’s most loyal customers on the planet.

San Juan Cancuc, a small community in Chiapas known for its consumption of Coca-Cola

A Coca-Cola van in the narrow streets of San Cristóbal

The signs are everywhere. Red trucks emblazoned with the curly white logo are familiar sights in towns and far-flung villages and on the winding, mist-shrouded mountain roads that connect them. Coca-Cola fridges occupy the most visible spots in most corner shops, while billboard adverts are so widespread they often end up as building materials for the very poor.

A celebration in the village of Zinacantán, with dancing, singing, alcohol and soft drinks

No gathering to celebrate a birth, a marriage or a patron saint is considered complete without Coke for the guests. Strikingly, Coca-Cola has become an integral part of indigenous religious observance and healing ceremonies, which are often intertwined with the Catholic pantheon but operate autonomously from the church. A bottle of Coke, believed to feed the good spirits and help the sick, is today as central a feature of many public and private rituals as incense, candles and sacrificial chickens.

A woman in front of an altar at her home in El Pinar.

Coca-Cola has become so intertwined with the local culture that is part of spiritual ceremonies such as this one in Tenejapa.

Pascuala is a pulsadora, a type of healer. Several years ago she started using Coke in her ceremonies

“Coca-Cola is sweet, so the spirits will appreciate it, and it also has certain healing properties” said Pascuala, a traditional healer from El Pinar.

But the intertwining of Coca-Cola with local tradition in Los Altos has contributed to the rise of a health emergency that activists accuse authorities of not taking seriously enough.

Coca-Cola is sweet, so the spirits will appreciate it, and it also has certain healing properties Pascuala, a healer

Type-2 diabetes is now firmly established as the biggest killer in the region, according to a study of death certificates between 2008 and 2012 in three municipalities. Jaime Page, a medical anthropologist who carried out the study, says the government has sought to keep diabetes mortality out of official statistics to avoid looking bad. Other health problems related to excessive sugar consumption, such as tooth decay, are also rampant.

“The consumption of soft drinks here is really terrible, and even with diabetics themselves it can seem impossible for them to stop,” Paige said. “I think it might be a lost battle.”

Sanando Heridas is a free and itinerant healthcare system for indigenous people. Rosa is pregnant and has comes to check on the baby and her glucose level

The story of how Coca-Cola became so deeply embedded in this verdant land of age-old traditions and minimal disposable income goes back to the 1960s when local indigenous leaders, with state backing, began accumulating power in religious, social and economic spheres. This included taking control of the concessions for the distribution of Coca-Cola and, initially, Pepsi too.

Paige says this happened at the same time as evangelical churches were making inroads in the area and pressuring indigenous communities to stop drinking alcohol. This combination led indigenous religious leaders to start substituting Coca-Cola for the local firewater, called pox, which they had long used to feed the spirits in their rituals.

In the Merced church in San Cristóbal, indigenous people have their own altar where they pray to the Virgin Mary as well as the spirits of nature. Healers at the church use soft drinks instead of the traditional pox, a very alcoholic drink prohibited by the Catholic church

The seal of celestial approval not only helped create a belief that Coca-Cola had the power to heal but also fuelled its march to becoming a symbol of social status and good hospitality. On more prosaic terrain, Coke also began to replace a traditional drink made of fermented corn dough, called pozol, which was once the main way peasants topped up their energy during long days in the fields. Today they are much more likely to reach for a sugar-packed soft drink.

Fensa, the Coca-Cola plant of San Cristóbal, Chiapas.

Coca-Cola’s colonisation of Los Altos was also accelerated by the construction of a bottling plant just outside San Cristóbal de las Casas, the area’s main city, in the 1990s. The plant today supplies much of the south of Mexico, and it has always paid particular attention to the local market.

Lunchtime during a celebration in Zinacantán.

Marketing strategies have included huge billboards with smiling indigenous models, religious references and slogans written in indigenous languages, as well as the proliferation of points of sale no matter how small the volumes shifted.

Marcos Arana, a medical doctor and activist based in San Cristóbal, likens the strategy to drug gangs penetrating deep into communities via large networks of small dealers driven primarily by the need to feed their own habits.

Tania, aged three, a Coke drinker, has had four milk teeth removed.

Arana says the addiction starts ever earlier. A recent study in an indigenous community found that 15% of children aged one or two regularly drank soft drinks, as did 3% of babies under six months.

Soft drinks in a shop in San Juan Chamula.

Coca-Cola’s penetration of the market in Los Altos has also been aided by a strategy of charging less in remote rural areas where a Coke in a returnable glass bottle is often scarcely more expensive than bottled water. As in most of Mexico, clean drinking water is not generally available even to those who can count on running water in their homes, which means many turn to soft drinks for basic hydration.

The irony of this is clear in an area known for its constant downpours and abundant springs, such as the one that attracted the Coca-Cola bottling company. Local activists say the company has so overexploited the spring that the city of San Cristóbal is now facing water shortages.

A small river whose water level has decreased significantly.

People collect rainwater in a cistern and store it in plastic bags.

A well that extracts fresh water from a volcano basin. The bottling plant has permits to extract more than 300,000 gallons of water a day as part of a decades-old deal with the government that critics say is overly favourable to the plant’s owners.

The activists allege this has been possible in part because Coca-Cola has friends in high political places. Between 2000 and 2006 the country’s president was Vicente Fox, a former head of Coca-Cola Mexico.

It all adds up to a perfect storm of sugar-related health issues in Los Altos. María del Socorro Sánchez, who is in charge of nutrition at the main hospital in San Juan Chamula, says only about one in 10 of the indigenous patients with diabetes accept there is any need to cut out sugar-packed drinks. “They just don’t believe that it is bad for them,” she said.