Simply examine the research... Some canned foods actually yield higher amounts of essential nutrients than their fresh or frozen counterparts as the cooking process concentrates the food.  In addition, in some cases, the heating process used in canning enhances the degree to which some naturally occurring, disease-fighting compounds are absorbed by the body.

See these studies for additional canned food nutrition information:

• Rutgers University, "Development of a Self-Directed Home Kitchen Makeover for Mothers of Young Children," - 2009
• Rutgers University, "Improving the Nutritional Quality of the Home Food Environment using Self-Directed Home Kitchen Makeovers," - 2009 
• Rutgers University, "Differences in Food Supplies of U.S. Households with and without Overweight Individuals" - 2009 
• Rutgers University, "Mothers of Young Children Cluster into 4 Groups Based on Psychographic Food Decision Influencers” – 2008 
• Rutgers University, “Food Choice Influencer of Mothers of Young Children” – 2008 
• Rutgers University, "State of the American Diet Study" - 2007
  
  
  
  
• University of California, Davis Nutrition Comparison Study "Nutritional Comparison of Fresh, Frozen and Canned Fruits and Vegetables" Part 1, Part 2 (PDF format)
  
  
  
  
• University of Illinois Study "Nutrient Conservation in Canned, Frozen and Fresh Foods"
  
  
• University of Massachusetts Study (PDF format): "Nutrition Study Phase I, Phase II and Phase III"