WITH a Nobel peace prize in one pocket and invitations from presidents and prime ministers in another, Muhammad Yunus is arguably the world’s most popular banker.

As the brilliant economist who turned a $27 experiment in rural Bangladesh into an $8 billion (£5 billion) microlending empire, Yunus has been feted for his creation of the Grameen bank, a hugely successful and much imitated project that lends small amounts of money to some of the poorest would-be entrepreneurs.

His work has won praise from presidents Barack Obama, Jimmy Carter and Bill Clinton. Obama said Yunus “had changed the world” while Carter said he had brought something “more valuable than a plate of food — security in its most fundamental form.” Investors in microfinance won Clinton’s approval for making money “the old-fashioned way, in a real economy, based on real people doing real things for a real rate of return”.

Yunus has drawn attention by signing deals with Jack Ma Yun, a Chinese internet entrepreneur who wants to set up microcredit ventures in Sichuan and Inner Mongolia, and with Carlos Slim, the Mexican telecoms billionaire who is backing a $45m microlending scheme in Mexico’s Oaxaca state.

He is also facing a different kind of attention. A pair of academic studies on the impact of the microfinance business has raised questions about Yunus’s impact in alleviating poverty.

“Microcredit is not a transformational panacea that is going to lift people out of poverty,” said Dean Karlan, a Yale economics professor who studied the phenomenon in the Philippines. “There might be little pockets of people who are made better off, but the average effect is weak, if not non-existent.”

Grameen’s previously lauded success provoked a headlong rush around the world to cash in on the microcredit trend, prompting warnings that a new lending “bubble” was being created.

Yunus has long argued that Grameen-style finance is unlike traditional banking and largely immune to the forces of recession that have crippled the global economy.

“We are not paper-based, paper-chasing banking,” he said on a recent visit to Japan. “When we give a loan of $100, behind that $100 there are chickens, there are cows. It is not something imaginary.”

Yet a series of commercial ventures sponsored by Grameen — and evidence of a shift from philanthropic to profit motives in similar projects around the world — has rung alarm bells at the charities and development institutions that finance much of the microlending.

While few dispute Grameen’s success in improving the lives of many Bangladeshi women — the principal recipients of small loans intended to help them start their own businesses — economists and poverty experts note that little research has been done on the net effect of microlending compared with, for example, constructing a rural factory that creates hundreds of jobs.

In the Philippines study, Karlan and a colleague, Jonathan Zinman, examined users of a microcredit bank to see what differences existed between poor people who received loans and those who were denied.

Their answer was disheartening. Not only were there few significant differences between the two groups over a number of months, but many of the loan recipients used their funds for household expenses instead of setting up businesses. Some bought new televisions.

A similar study of micro-lending in Hyderabad, India, found no effect on health and education in families that received small loans. A study by poverty researchers at the Massachusetts Institute of Technology found minor benefits, but the real problem, according to Esther Duflo, an MIT professor, was the expectation aroused by the glowing image of Grameen.

“Why did we expect all these things to happen?” Duflo told The Boston Globe. “Microlending is useful, but it’s not like the miracle drug to end poverty.”

Eyebrows have also been raised at Grameen’s expansion into other forms of business. One of its subsidiaries owns 38% of Bangladesh’s largest mobile phone provider, which is seeking to raise $140m this month with a public offering of shares.

In India, Vikram Akula, the founder of SKS Microfinance, the country’s largest micro-lending bank, says he is modelling his growth plans on “Coke, Starbucks and McDonald’s”. He describes Yunus as his “inspiration”, but says it is time for a younger generation of bankers to “push it to the next level ... with the unabashed goal to be extremely profitable”.

However, the evidence so far is that microfinance “didn’t transform lives to the extent suggested by the hype”, said Karlan.

Peter Schaefer, an expert on poor countries, acknowledged that Yunus and other prominent advocates for the poor were “poverty-fighting visionaries ... but their brilliant ideas have had limited real-world impact. Sadly, the honours they have received often hide this hard truth, limiting vital criticism of their work”.

Defenders of Yunus have argued that the benefits of microlending will be proven and that studies based on little more than a year of research provide an incomplete picture.

How it works

* Money is lent to groups too poor to have access to bank loans

* The loans are small, often between £50 and £200

* Interest rates are far lower than charged by loan sharks

* Loans, say, for a sewing machine, are intended to encourage enterprise and prosperity

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive