No doubt you've heard countless times that you should eat plenty of fresh vegetables. Vegetables, of course, are loaded with vitamins, minerals, phytonutrients and flavonoids, many of which you can't obtain from other food sources. The conventional thinking is that fresh vegetables are superior to canned vegetables because the canning process robs the vegetables of vital nutrients. Certainly, the flavor and texture of canned vegetables pales in comparison to fresh vegetables. However, the extent to which you effectively lose nutrients depends on various factors, such as the type of nutrients in question, how fresh your fresh vegetables actually are and how you prepare your vegetables.
Canning Process
The canning process typically involves harvesting vegetables at their peak of freshness, heating them to a high temperature to eliminate bacteria and then sealing them in an airtight container. For vegetables that are nonacidic, the sterilization must reach well above the boiling point of water, which usually entails the use of a pressure canner. The can usually has a saline solution, acid base or some other environment that is inhospitable to microbes. The airtight packaging prevents microorganisms from feeding on your sterilized vegetables before you do. Canned vegetables have a typical shelf life of one to two years.
Vitamins
The University of Illinois Department of Food Science and Human Nutrition released a study in October 1997 that compared the nutritional value of canned versus fresh vegetables and fruit. It concluded that, overall, canned and frozen vegetables compare favorably to fresh vegetables in terms of nutrition. However, water-soluble vitamins such as vitamin C and the vitamin B-complex group leach out of vegetables during the canning process. For example, 10 percent to 90 percent of vitamin C is lost from a vegetable during canning. Much of this vitamin ends up in the canning liquid, however. From 10 percent to 60 percent of the B vitamins are lost during blanching. Fat-soluble nutrients, such as vitamins A and E, and cartenoids, such as lycopene, are sensitive to heat and light, but high-pressure blanching in water causes little loss. Canned tomatoes contain a higher lycopene content than fresh tomatoes, perhaps because heat causes the release of the nutrient from its cellular matrix.
Mineral and Fiber Content
The dietary fiber in vegetables provides numerous benefits that include assisting digestion, reducing appetite, stabilizing blood sugar and enhancing cardiovascular health. Minerals in vegetables contribute significantly toward providing essential nutrition unavailable in many of the other foods you eat. Canning does not affect the content of minerals or dietary fiber. In fact, the high heat might enhance the solubility of the fiber and its usefulness.
Loss of Nutrients in Fresh Vegetables
To make a fair comparison between fresh and canned vegetables, consider the circumstances of how you buy, store and prepare fresh vegetables. By the time you consume your vegetables, fresh, frozen and canned vegetables may be quite similar in nutrition, depending on how they are processed and prepared. Unless you are growing the vegetables yourself and picking them from your garden, chances are that the vegetables have been grown someplace far from where you live. They've likely been picked well before they have reached maturation and have developed the full range of vitamins and minerals. Also, many people only grocery shop once or twice a week, or even less often than that. So, unless you buy fresh vegetables daily, your so-called fresh vegetables can sit around in your fridge for quite a few days. Vitamin C degrades quickly after harvest and as much as 77 percent of the vitamin C in green beans can be lost after seven days of storage at 39 degrees Fahrenheit. Also, if you boil or steam your vegetables, you lose some of the same vitamins that are lost during the canning process. Typically, canned vegetables are cooked for a much shorter time than fresh or frozen vegetables, so they tend not to lose as many vitamins during their brief cooking. If you cook them long and hard, however, you will lose more of the water-soluble vitamins.
References
- Dr. Briones Medical Weight Loss Center: Canned and Frozen Fruits and Vegetables for Weight Loss
- Eating Well; Fresh vs Frozen Vegetabes: Are We Giving Up Nutrition for Convenience?; Rachael Gorman; November/December 2007
- Knight Ridder/Tribute Business News; Waiting to Eat Fresh Vegetables Means Loss of Nutrients; March 27, 2005
- NutriCan: Study Findings: Comparison of Selected Fresh, Canned and Frozen Fruits, Vegetables, Legumes and Protein Foods
- NutriCan: A Study of Canned Food Nutrition
- Steel Market Development Market; Executive Summary: Nutritional Comparison of Fresh, Frozen, and Canned Fruits and Vegetables; Joy Rickman, et al.
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