The Bloomberg Commodity Index, which tracks the price of 22 different commodity investments, recently traded at its lowest level since 2002. Stocks of commodity-exposed companies have suffered over the past year, but investors with direct stakes in the commodities themselves have been hit hardest.

Here’s a look at five commodities that have lined the downward-spiral path over the past year.

1. Silver

Silver prices have plummeted as investors anticipate money flowing out of precious metals when the Federal Reserve begins raising interest rates. The iShares Silver Trust (ETF) SLV 0.59% is down nearly 25 percent in the past year.

2. Wheat

A huge global wheat supply glut has weighed heavily on wheat prices over the past year, and a recent report by the U.S. Department of Agriculture indicates that world stockpiles continue to grow. Shares of the Teucrium Wheat Fund WEAT 1.83% have lost more than a third of their value in the past year.

3. Natural Gas

According to the U.S. Energy Information Administration, dry shale gas production is at all-time highs, driven by huge increases in recent years in the Marcellus shale. Shares of the United States Natural Gas Fund, LP UNG 5.22% are down nearly 44 percent in the past year.

4. Lean Hogs

While beef supply has been under pressure lately, the USDA expects pork production to increase 5.4 percent in 2015. Soft pork demand has severely impacted prices over the past year. With beef prices on the rise and lean hog prices down more than 44 percent in the past year, the E-TRACS USB Bloomberg Commodity Index Exchange UBC has split the difference, falling only 4 percent.

5. Crude Oil

The collapse in crude oil prices due to a global supply glut is at the center of the downward spiral in commodity prices in the last year. The United States Oil Fund LP (ETF) USO 0.6% has fallen more than 50 percent.

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