Why would an investor want to invest in one of these sub-sectors? One reason is portfolio protection against the deleterious effects of rising energy prices. These negative effects are eventually manifested in the stock market, through demand destruction, higher producer costs, and ultimately, less money in consumers' pockets. Another reason is the general protection against inflation. While the Fed denies it, some still expect the launch of QE3. Most of the commodity subsectors will provide a measure of protection here. However, if that is the extent of the reason, there are Alt ETFs that offer a basket of commodities across all of these subsectors.Another reason is protection against erosion of the dollar's buying power. For this, an entire other category of Alt ETFs are specifically suited - currency ETFs. There are many ETFs that invest in foreign currencies. By so doing, investors benefit from the appreciation of that currency relative to the dollar (which is the same thing as saying the depreciation of the dollar in terms of another currency). This can be the major currencies (Japanese Yen, Euro, British Pound, etc.) or more exotic currencies, like those of the BRIC countries (Brazil, Russia, India and China). Again, there are baskets for investors that do not want to be country-specific.