NEW YORK ( TheStreet) -- Many investors may hold a risky amount of commodities exposure in their portfolio due to cross exposure between various asset classes.Most commodity exposure comes from equity, futures and physical commodity ETFs. Popular equity-based funds such as Market Vectors Agribusiness ETF ( MOO) and iShares Dow Jones U.S. Oil Equipment and Services Index Fund ( IEZ) track baskets of firms dedicated to the production of various hard assets. Funds such as United States Natural Gas Fund ( UNG) and PowerShares DB Agriculture Fund ( DBA) track the price movements of futures contracts, providing investors with more direct exposure to physical commodities. Finally, investors can gain pure access to a physical stockpile of precious metals using products such as SPDR Gold Shares ( GLD) and ETFS Physical Palladium Shares ( PPLT). While I believe having some exposure to commodities is essential to playing the current global economic arena, it is very easy for an ETF investor to take his interest in hard assets too far. To exemplify, allow me to introduce you to Commodities Rex. The Commodities Rex has a passion for all things commodities. Whether it is gold, coal, oil, natural gas, or agriculture, this investor craves it and looks for any way possible to get exposure to it. KOL) as evidence of strong equity positions and use funds such as Market Vectors Russia ( RSX) or iShares MSCI Australia ( EWA) to satisfy his need for international exposure. Finally, a physically-backed gold ETF such as GLD will round out the portfolio, providing the investor with welcomed protection against inflation and market jitters. Separately each of these funds is strong and boasts adequate liquidity. However, when it comes to diversification, the Commodities Rex misses the mark. By lumping all of these holdings together this investor may think that he's taking a diversified approach to playing the markets when in fact he has constructed a portfolio that has overwhelming exposure to the commodities market and ultimately ignores other important facets of the global markets.