NEW DELHI -- They are every marketeer's dream and the future of the world economy -- now Asia's aspirational middle classes have been laid bare in a major new study focusing on their astonishing growth.

The Asian Development Bank forecast in the research released Thursday that over the next two decades another 800 million people will make the transition from poverty to the middle classes, assuming economic development continues.

Their elevation "may present many challenges, but it will also open up new and unprecedented opportunities for the region and for the world," the ADB concluded.

The study, "The Rise of Asia's Middle Class", also sought to shed light on the characteristics of this burgeoning cross-section of society, concluding that they share many traits with their counterparts in the wealthy West.

The Asian middle classes are likely to be educated, live in urban areas and have fewer children and more progressive values. They are prone to over-eating and under-exercising, and are keen buyers of cars and household electronics.

Not surprisingly, the two countries with the biggest populations, China and India, are set to see the biggest increase in middle-class Asians, with more than a billion people due to be in the higher category in each country by 2030.

China has been much more successful than India in elevating poor people, with 63 percent of its population, or 817 million people, in the higher income group in 2008 -- a large proportion of the 1.9 billion middle-class citizens in emerging Asia.

India's middle classes numbered 274 million in the same year, or just a quarter of its 1.1-billion-strong population, according to data cited by the ADB.

"Projections suggest that by 2030 much of developing Asia will have attained middle class and upper class status," said ADB chief economist Jong-Wha Lee in the foreword to the study.

The report defined the middle class as those people consuming between two to 20 dollars a day, and looked at "emerging Asia" -- the whole region excluding Japan and Korea.

Rising incomes are expected to be the main motor for the global economy as consumers buy increasing numbers of refrigerators, cars, mobile phones and holidays.

Consumer spending in the region was clocked at 4.3 trillion dollars in 2008 and is forecast to grow eight times to 32 trillion in 2030. At this level, it would account for 43 percent of the world's total consumption, the ADB said.

"Asia will play a primary consumer role in the future, switching from a major global producer to a major global consumer," Lee told reporters.

Such an explosion of consumerism carries significant social, political and environmental implications.

Climate change, environmental degradation, competition for water resources and land pressures are just some of the potential downsides of the rise of vast numbers of people seeking the material comforts familiar in the West.

There are also major public health considerations, the ADB said, with the Asian middle classes already showing signs of adopting entrenched Western habits of eating food that is high in calories and fat.

Diabetes, heart disease and cancer are on the rise.

"All indications are that in the next 20-30 years, Asia will be faced with an increasing number of chronic diseases on a scale previously unseen," the report said.

There is also a risk that major economic disruption -- another financial crisis, wars or large natural disasters -- could reverse the movement of people into higher income categories, the ADB said.

The Indian middle classes, most of whom are in the lower bracket of 2.0-4.0 dollars per day of consumption, are particularly vulnerable.

But the overall trend is positive from an economic perspective, the bank said, with increasing personal wealth creating a virtuous circle of enterprise.

Companies are innovating more and more to produce low-cost items for the Asian middle classes, the report said -- exemplified by India's Tata Nano car, the world's cheapest automobile.

There are also political implications for governments, which must satisfy the clamour for better public services and transparency from wealthier citizens who are more likely to be politically engaged, the ADB said.