The emerging markets consumer has been a compelling, yet flummoxing theme for investors -- the allure of newly affluent (and soaring numbers of) new entrants to the middle class in the emerging world is alluring. ETF sponsors have met that demand with an array of multi-country and country specific products.

All that said, the emerging markets consumer has not been a guaranteed winner for investors. For example, one well-known ETF offering exposure to the Chinese consumer is off 19.4 percent since its debut nearly three years ago.

For investors looking to dip their toes into some emerging markets consumer ETFs, a good news has arrived. A study by Boston Consulting Group shows consumer spending in China and India is expected to reach a combined $10 trillion per year by 2020, according to Reuters.

In the years leading up to 2020, Boston Consulting predicts consumers in China and India will spend a combined $64 trillion, Reuters reported. Growing middle classes in China and India, Asia's largest and third-largest economies, respectively, are expected to drive the consumer spending boom. Investors can prepare for the trend with the following ETFs.

EGShares Emerging Markets Consumer ETF (ECON) The EGShares Emerging Markets Consumer ETF is arguably the gold standard when it comes to emerging markets consumer-focused funds. Since this is an emerging markets fund, it is bound to be more volatile than a comparable U.S.-focused ETF. However, it should be noted that ECON is more allocated toward staples equities such as food, beverage and tobacco producers, not consumer discretionary.

However, ECON only features a 10.5 allocation to India and no exposure to China. Global X China Consumer ETF (NYSE: ) Investors looking for Chinese exposure might consider CHIQ, one of the more quiet ETFs with over $100 million in assets under management (it has almost $111 million in AUM). This is the fund referenced earlier that has lost 19 percent since inception. On the upside, CHIQ is the most direct route to the China consumer and the ETF is shedding its laggard status. As was predicted several months ago, CHIQ was poised for some upside and the ETF has delivered, soaring almost 6% in the past month.

The EGShares India Consumer ETF (INCO) Just as CHIQ in the world of China ETFs, INCO is an often forgotten member of India ETF universe. Perhaps that will change with if Boston Consulting's forecasts prove accurate.

INCO shares an important trait in common with ECON and that is the ETF is much more heavily exposed to staples than discretionary names. INCO is by no means the Consumer Staples Select Sector SPDR (XLP) in terms of being boring.

Then again, that might be a good thing and INCO might be telling investors the Indian consumer is already perking up. On the basis that stocks and ETFs are forward-looking assets, INCO's 41.3 percent year-to-date gain could be foreshadowing increased strength in Indian consumer trends going forward.

First Trust ISE Chindia Index Fund (FNI) The First Trust ISE Chindia Index Fund presents a useful option for investors on two levels. First, it eases the burden of picking between China and India. Second, the fund is not a full commitment to the consumer. FNI offers scant staples exposure, but discretionary names account for almost 23 percent of the fund's weight.

FNI's largest holding holding is not a Chinese or Indian company. That honor goes to high-end handbag maker Michael Kors (KORS), which represents 8.7 percent of FNI's weight.

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