When it comes to exchange traded fund (ETF) investing, it has become quite simple to build a narrow portfolio with these funds, with a very specific goal in mind. The choices will keep making the evolution of ETF investing quite dramatic.

Roger Nusbaum for Seeking Alpha has a few examples for investors who may wish to use a currency investment as a proxy for commodities.

His first example is the WisdomTree South Africa Currency (SZR) as a proxy for gold.

But if an investor holds SPDR Gold Shares (GLD), there can be somewhat of a negative correlation. South Africa has a few imbalances and is facing inflation, so the correlation of the two will get better. Instead, Nusbaum suggests CurrencyShares Australian Dollar (FXA). If your portfolio holds Australia already, however, then avoid over-allocation.

CurrencyShares New Zealand Dollar (BNZ) would be a better diversification tool, and many consider the kiwi to be a commodity currency, because of the amount of meat, dairy and wool that is produced in New Zealand. So, rather, BNZ could be an agriculture proxy, and it avoids the volatility of the agriculture funds.

Nusbaum is not suggesting you buy either ETF, he is showing investors how to recognize themes and using other methods to access various asset classes that may not be so obvious.

Read the disclosure, as Tom Lydon is a board member of Rydex Funds.

Tags: Agriculture, Australia, BNZ, Commodity ETFs, Currency ETFs, FXA, GLD, Metals & Mining, New Zealand Dollar, South Africa, SZR