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http://www.whfoods.com/genpage.php?tname=foodtip&dbid=27#title
(World’s Healthiest Foods is a terrific site with many recipes and vitamin/mineral/micronutrient listings for what they call “power” foods.)

Best ways to cook Swiss chard
While Swiss chard is a great vegetable to eat raw in salads and sandwiches, this versatile and nutrient-concentrated vegetable can serve as a great addition to most any cooked recipe. Yet, like with all foods it is important to consider how cooking can affect its nutrient content, taste, texture and color, so that you can insure that you are receiving the very best that this leafy green vegetable has to offer every time you eat it. While there are limited research studies on how to cook Swiss chard to maintain its optimal nutritional value, published studies all support what we emphasize on the World’s Healthiest Foods website: short cooking times are the best.

Nutrients in Swiss chard
Swiss chard is a power food, a storehouse of many different vitamins, minerals and nutrients. In fact, based upon the nutrient rating system we developed at the World’s Healthiest Foods, Swiss chard is an excellent source of 12 nutrients, a very good source of 6 nutrients and a good source of 5 nutrients. Swiss chard is a nutrition star!(link to either Food Rating Table or Nutritional Profile for chard).
As a member of the goosefoot family of plants (also called the chenopod family), Swiss chard is in the company of and beets (which originally and still grow wild around parts of the Mediterranean), quinoa (which originated in the valleys of the Andes and was a staple food for the Inca civilization) and spinach. Chard’s unique heritage as a member of the goosefoot family is one of the reasons it is so valuable nutritionally.

Short term cooking can best retain Swiss chard’s nutrients - focus on vitamin C

As noted above, cooking Swiss chard for minimal amounts of time is the key to maximizing it nutrient profile. This is because many of the nutrients concentrated in Swiss chard are susceptible to damage from heat and water.

Looking to the 12 nutrients for which Swiss chard is an excellent source, let’s take vitamin C as an example of how cooking may impact the nutrient content of this vegetable. Studies that have examined the impact of cooking upon vitamin C have shown that short-duration cooking (3-6 minutes) resulted in vitamin C loss of 25% or less while studies involving longer cooking times (10-20 minutes) have shown that 50% or more of the vitamin C may become lost.

How important is it to preserve this vitamin C? Consider these numbers: in one cup of chard, costing you only 35 calories, there are 32 milligrams of vitamin C. These numbers rank chard right alongside of freshly squeezed organic orange juice as a source of vitamin C! Cooking the chard for too long is like leaving half of your freshly squeezed organic orange juice sitting in the glass.

Short term cooking can best retain Swiss chard’s nutrients - focus on potassium and magnesium

Other examples of how cooking can impact the nutrient content of Swiss chard involve the minerals in which Swiss chard is concentrated. Included in chard’s “excellent amount” category are the minerals potassium and magnesium, and both are particularly vulnerable to reductions from cooking. Even blanching for several minutes may greatly reduce the content of these minerals. Applying insights gleaned from studies focused on nutrient losses from cooked spinach, where blanching for several minutes resulted in a reduction of over 50% of potassium and approximately one-third of magnesium, we once again see how minerals are at risk for nutrient loss during cooking and how important using minimal cooking times can be.

How cooking affects oxalates in Swiss chard

Swiss chard is one of the vegetables that contain oxalates, naturally-occurring substances found in plants, animals, and in humans. Although there are a few, relatively rare health conditions that require strict oxalate restriction (hypertext to oxalate article here), for the vast majority of individuals, oxalate-containing foods should not be a health concern.

For those concerned with oxalates, it turns out that cooking actually has a relatively small impact on the oxalate content of foods. Repeated food chemistry studies have shown no statistically significant lowering of oxalate content following the blanching or boiling of green leafy vegetables.

You should not expect more than a 5-15% reduction of oxalate content when cooking Swiss chard. Since many more vitamin and minerals are lost from overcooking more quickly than oxalates, it does not make sense to overcook oxalate-containing foods in order to reduce their oxalate content. Doing that will only result in a diet that is much less nutritionally beneficial while only minimally lower in oxalates.*

Maintaining vibrant color

While the rich colors of Swiss chard can be attributed to a host of different phytonutrients, chlorophyll is a major contributor to its rich green color. Chlorophyll contributes a green color to vegetables and plants since it reflects sunlight at exact appropriate wavelengths for our eyes to detect them as green.

Prolonged cooking results in a dramatic loss of chlorophyll. Excessive heating results in the removal of the magnesium from the center of the chlorophyll molecule causing it to turn into a molecule called pheophytin, which results in a noticeable change in color from from bright green to olive-gray. Therefore, to maintain the vibrant green color of Swiss chard and the potential health benefits supplied by the chlorophyll phytonutrients it is important to cook it for minimal amounts of time.

In the world of processed food, you can never trust your senses to tell you whether a food is nutritious or not. There are too many ways for a food manufacturer to trick your taste buds and your eyes. There are artificial flavors and artificial colors in the majority of non-organic, processed foods. But in the world of cooking and organically-grown food, it is amazing just how much you can trust your senses! You can depend on your taste buds and your eyes! When chard’s color starts to look lifeless, guess what? The chard is losing something - in this case, the magnesium found in its chlorophyll.

Enhanced taste and texture

One of the reasons that many people don’t like green leafy vegetables is that they equate these foods with a soggy, limp texture that also can contribute to a taste profile that is compromised. Yet, this texture and taste are not inherent to the vegetables themselves but are caused by the overcooking that the vegetable has experienced either in the home or in a restaurant. Therefore, by cooking Swiss chard for only a few minutes as opposed to a longer period of time, you will not only be able to enjoy the nutrients inherent in this vegetable, but its great taste and texture.

Once again, your senses can be your guide here. If you had a plant at home, or in your garden, and it started looking limp, you would automatically think that it had either too much water, too little water, or had been exposed to too much sun. Assume the same thing about the chard you are preparing: too much heat, too much contact with boiling water or steam and you’ll observe the exact same consequence.

Practical tips

To maximize the content of the nutrients of which Swiss chard is concentrated, quickly cook this leafy green vegetable, covering the pot or pan. Boiling for 2-3 minutes is the method we highly suggest. Not only will this method help to retain nutrient content, but will provide you with a vegetable bursting with taste, great texture and bright color.

References

Kimura, M. and Itokawa, Y. Cooking losses of minerals in foods and its nutritional significance. J Nutr Sci Vitaminol (Tokyo). 1990; 36 Suppl 1:S25-32; discussion S33.

Mangels, A. R.; Block, G.; Frey, C. M.; Patterson, B. H.; Taylor, P. R.; Norkus, E. P., and Levander, O. A. The bioavailability to humans of ascorbic acid from oranges, orange juice and cooked broccoli is similar to that of synthetic ascorbic acid. J Nutr. 1993 Jun; 123(6):1054-61

*People who habitually form kidney stones need to be concerned about oxalates. —TAC