Fresh spinach is a great addition to a healthy salad. Compared to iceberg lettuce, which has virtually no nutritional benefits, spinach is loaded with vitamins, minerals and fiber.

Spinach is also convenient because it can be bought trimmed and prewashed in bags. But here's a tip: While many bags say the spinach is "triple washed," make it quadruple washed before you eat it.

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New research from the Bourns College of Engineering in California found that more than 90 percent of the bacteria in prewashed baby spinach survived after being rinsed in the processing plant. The researchers noted that about 20 percent of foodborne bacterial outbreaks from 2003-2008 were caused by "leafy green produce." Most of the 3,000 Americans who die each year because of foodborne illnesses are 65 and older.

The take-away: Rinse all fresh produce before you eat it, even if it comes "prewashed."