Fears are growing for the fate of thousands of young girls in rural Mauritania, where campaigners say the cruel practice of force-feeding young girls for marriage is making a significant comeback since a military junta took over the West African country.

Aminetou Mint Ely, a women's rights campaigner, said girls as young as five were still being subjected to the tradition of leblouh every year. The practice sees them tortured into swallowing gargantuan amounts of food and liquid - and consuming their vomit if they reject it.

"In Mauritania, a woman's size indicates the amount of space she occupies in her husband's heart," said Mint Ely, head of the Association of Women Heads of Households. ''We have gone backwards. We had a Ministry of Women's Affairs. We had achieved a parliamentary quota of 20% of seats. We had female diplomats and governors. The military have set us back by decades, sending us back to our traditional roles. We no longer even have a ministry to talk to." Mauritania has suffered a series of coups since independence from France in 1960. The latest, in August last year, saw General Mohamed Ould Abdelaziz seize power after the elected president tried to sack him.

A children's rights lawyer, Fatimata M'baye, echoed Ely's pessimism. "I have never managed to bring a case in defence of a force-fed child. The politicians are scared of questioning their own traditions. Rural marriages usually take place under customary law or are overseen by a marabou (a Muslim preacher). No state official gets involved, so there is no arbiter to check on the age of the bride." Yet, she said, Mauritania had signed both international and African treaties protecting the rights of the child.

Leblouh is intimately linked to early marriage and often involves a girl of five, seven or nine being obliged to eat excessively to achieve female roundness and corpulence, so that she can be married off as young as possible. Girls from rural families are taken for leblouh at special "fattening farms" where older women, or the children's aunts or grandmothers, will administer pounded millet, camel's milk and water in quantities that make them ill. A typical daily diet for a six-year-old will include two kilos of pounded millet, mixed with two cups of butter, as well as 20 litres of camel's milk. "The fattening is done during the school holidays or in the rainy season when milk is plentiful," said M'baye. "The girl is sent away from home without understanding why. She suffers but is told that being fat will bring her happiness. Matrons use sticks which they roll on the girl's thighs, to break down tissue and hasten the process."

Other leblouh practices include a subtle form of torture - zayar - using two sticks inserted each side of a toe. When a child refuses to drink or eat, the matron squeezes the sticks together, causing great pain. A successful fattening process will see a 12-year-old weigh 80kg. "If she vomits she must drink it. By the age of 15 she will look 30," said M'baye.

Historians say the practice dates back to pre-colonial times when all Mauritania's white Moor Arabs were nomads. The richer the man, the less his wife would do - the preference being for her to sit still all day in her tent while her black slaves saw to household chores. Ancient Berber quatrains laud tebtath (stretchmarks) as jewels. Even today lekhwassar (fat around the waist) is given lyrical pride of place and girls sent for fattening gain the stature of mbelha. They are taught to sit in the lotus position, speak softly, use utensils and to emulate the exemplary lives of the Prophet Muhammad's wives. Fattening of girls is practised beyond Mauritania, in northern Mali and rural Niger - areas conquered, along with half of present-day Spain and Portugal, by the Almoravid dynasty in the 11th century. The practice of fattening also continues in Nigeria's Calabar state and north Cameroon.

The resurgence of the practice in rural Mauritania is a depressing setback for campaigners after previous education and awareness campaigns were apparently having a tangible effect. "The challenge we face is that these girls live in rural areas and do not have access to information," said Ely. "Until the military coup last year, we had made strides. Ten years ago we ran information campaigns about the dangers of cardiovascular disease and diabetes. The government even commissioned ballads condemning fattening." Many middle-class Mauritanians, among a population estimated at three million, claim the practice of force-feeding no longer exists.

Political scientist Mohamed el-Mounir, 38, claimed western influence had wiped out the allure of feminine fat. "Fattening is something from the 1950s. These days girls watch fashion shows on television. Their role models are American actresses or Lebanese singers in sexy dresses. Girls do sport. Yes, Mauritanian men like slightly round women. But there is no way we want them obese."

Health and development consultant Mounina Mint Abdellah, 51, said she was force-fed as a child by her mother's family. "Things have changed tremendously. When I left school in 1980 it would have been unthinkable for me to go abroad to study. But now, 30 years later, my daughter is doing her master's degree in France. We owe a great deal to the fact that all girls are now expected to go to school. These changes have had a tremendous impact on ancestral practices. Fattening just seems out of date to a large part of Mauritanian society."

But Ely and M'baye insist the fat "ideal" is back. Ely cites the life-threatening weight-gain practices of some grown women. "To remain fat, as adults, they take animal hormones or buy prescription drugs with appetite-enhancing side-effects. A woman died in hospital in Nouakchott last week. I'm afraid this problem is still very much with us."

• Additional reporting by Manon Rivière in Nouakchott

• This article was amended on Thursday 9 July 2009. The headline was changed from "Girls being force-fed for marriage as junta revives fattening farms" because it did not accurately reflect the article which said the governing military regime in Mauritania was being blamed by women and children's rights campaigners for a return to traditional roles and a resurgence of such practices as leblouh. The report did not say that the government had revived this practice. This has been corrected.