There is another name for Swiss chard - actually several - depending on where in the world you are. In South Africa it's actually referred to as spinach. In the United Kingdom, as perpetual spinach. In the United States, on more rare occasions you might hear it called bright lights and silverbeet, especially coming from the mouths of older generations. Mangold, crab beet and seakale beet are among the least common names used.
Where did Swiss chard originate? Is it really Swiss? Ironically, it's not even native to Switzerland nor is it very popular there! The exact origin of the name is unknown, though some speculate it may have had something to do with one of the earliest botanists to describe it - Gaspard Bauhin (who was Swiss) and lived 1560 to 1624 (1).
What is it exactly?
What is a chard vegetable? Is Swiss chard a beet? Yes, it is. The species Beta vulgaris is responsible for not only this plant, but also the common root vegetable beetroot or garden beet (a red or yellow beet). The sugar beet is another, which is a common source used along with sugar cane for producing white table sugar.
Difference between Swiss chard and rainbow chard?
There is no difference, they all come from the same species. Rainbow Swiss chard simply refers to a mix of more than one variety. Often times that's green/white, red, and yellow chards. All of these come from the Beta vulgaris species.
We are unaware of published ORAC values for rainbow chard to do a comparison. Though based on this test which was for the red variety, one can conclude that any rainbow mixture would likely be less than this value. Why? Because the red pigments contain anthocyanins, a category of antioxidants you will find little to none of in other varieties. For that reason, the type of chard which is most healthy for you is likely the red variety.
Is Swiss chard good for you?
There are actually many people who are under the assumption that chard is poisonous, which is simply not true.
That false perception is due to its confusion with rhubarb, whose leaves should not be eaten because indeed, they do contain poisonous substances; high amounts oxalic acid, which is a nephrotixc and corrosive acid. While it shouldn't be lethally toxic, in excess it is poisonous to humans, dogs, cats, and likely all mammals, causing digestive side effects such as watery diarrhea and spasmodic cramps, as well as other serious symptoms like elevated ALT serum levle, hemorrhaging, hemostasis, and neonatal jaundice.
The exception however is pets. Giving Swiss chard in any amount to your pets, whether that be dogs, cats, rabbits, guinea pigs, etc. is not recommended as being from the nightshade family of plants, they can reportedly cause sores in the mouth as well as skin problems. As far as amphibians and reptiles like turtles, lizards, and iguanas, ask your vet before giving it to them. Likewise for other nightshades; onions, potatoes, spinach, collard greens, and tomatoes are a few examples. Also chard contains high amounts of oxalic acid which can cause kidney stones and deplete the body of calcium.
For that same reason, people who are more susceptible to kidney stone formation and are on a low oxalate diet should probably avoid this vegetable. Eating raw chard could be bad for you. Cooking it greatly reduces the amounts of oxalates, but eating that still might not be a good idea.
For everyone else, chard is a healthy choice. Not only for cooked recipes, but even eating raw chard as a replacement for lettuce in salads. The fibrous stems, especially when raw, can be difficult to digest for some, so leaving those out might be a good idea for you if you have GI motility disorders.
Nutrition and health benefits
The antioxidant activity and phenolic compounds of Swiss chard are relatively high. In fact the ORAC value you see reflected above was taken from a report published by NASA in 2015 which was evaluating various nutritional leafy greens for growing on the International Space Station. The variety tested was red Swiss chard and its anthocyanin content was 12.47 mg/g.
NASA's test looked at beet, Chinese cabbage, two types of spinach (tyee and flamingo), mizuna, red leaf lettuce, and green leaf lettuce. Among those, the Swiss chard tested highest for both lutein (5.94 mg/g DM) and zeaxanthin (0.04 mg/g DM). Its lutein concentration was over 100% higher than Chinese cabbage and more than 40% higher than the mizuna and red lettuce. Those without red pigments - both spinach types and green leaf lettuce - had none at all. The health benefits of lutein and zeaxanthin are that they are carotenoids which accumulate in the retina of your eye. It is believed they function by helping to filter out and protect your eyes from UV rays and excess light, which would be even more important for NASA's needs; protecting the eyes of astronauts who are bombarded with light that is not softened by an atmospheric shield.
The vitamin content of chard is particularly noteworthy for vitamin K, an important nutrient which benefits your bones. While over 4x as much as lettuce, red Swiss chard's concentration took a distant second place to mizuna, which was almost 200% higher (2.32 mg/100g versus 0.79 for chard). Examples like this reinforce why it's important to consume a variety of different leafy greens, as some are higher in certain nutrients like vitamin K, while others have higher amounts of carotenoid content.
Other nutritional facts for 100 grams of red chard include 50% of your daily value of vitamin C, 122% of vitamin A, 20% of magnesium, and 10% of potassium. Data for all other essential vitamins and minerals came in at less than 10% of your daily value. At only 19 calories for that 100 grams, chard is good for you with zero guilt!
In addition to the red and yellow varieties, there is white or green Swiss chard. To get the most health benefits possible, have some of each. The colored varieties - the reds and yellows - will provide carotenoids and anthocyanin activity which you may not get from the green chard.
Research Support, U.S. Gov't: NASA, Selection of Leafy Green Vegetable Varieties for a Pick-and-Eat Diet Supplement on ISS PDF July 2015