Nutrients of the Rainbow – Blue/Purple

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Welcome to the final installment of the nutrients of the rainbow series— blue and purple nutrients! So far we’ve learned about anthocyanins, carotenoids, and chlorophyll, which are the nutrients responsible for the red, orange, yellow, and green colors of foods.

For the last segment – blue and purple – we will revisit anthocyanins and introduce betalains, a similar category of chemicals in plants that produce color. We’ll learn about the similarities and differences between these molecules, highlight two superfoods – blueberries and beets, and provide a recipe for beet kvass.

Anthocyanins Revisited

Recall from the red segment of the rainbow series that water-soluble antioxidant molecules called anthocyanins are responsible for the red pigment of strawberries, raspberries, cranberries, and grapes. Anthocyanins can also be blue or purple, depending on which anthocyanins are present and the pH of their environment.

Take purple cabbage, for example. Its purple color results from a combination of anthocyanins present in the plant, mostly cyanidins. If you chop the cabbage and boil it in water for a few minutes, a purplish liquid appears. Add baking soda, and the solution turns blue. Add acid and the solution turns pink.

This is why sauerkraut made with purple cabbage turns a bright magenta pink. As bacteria present on the cabbage leaves ferment the natural sugars, the pH of the solution lowers and changes the appearance of the anthocyanin’s color.

RECIPE >>> Tangy Probiotic Sauerkraut

Solutions made from purple cabbage work well as natural dyes for Easter eggs or fabrics. Here’s a fun experiment to introduce the concept of pH changes to kids using purple cabbage.

Purple cabbage, purple sweet potato, blackberries, currants, and blueberries are the most common foods rich in blue and purple anthocyanins.

Naturally blue foods are actually pretty hard to come by, as blue is the rarest naturally occurring color in the plant world. Next let’s highlight a super special blue food.


One of the richest sources of antioxidants per gram, blueberries are truly a superfood. Not only are they high in anthocyanins, which contribute to their color, they also contain numerous other phytochemicals, including quercetin, a polyphenol that is found on their skins, and resveratrol. In addition, blueberries are a good source of vitamin C, vitamin K, manganese, copper, and fiber.

The antioxidant and anti-inflammatory properties of blueberries make this fruit an ideal candidate for the study of its potential therapeutic benefits for chronic health issues that plague the world today. As a result, a large body of research is devoted to the effects of regular blueberry consumption or supplementation with blueberry products on cardiovascular disease, type 2 diabetes, cognitive function, aging, and weight management.

Though research of this sort is inconclusive and unlikely to draw a direct connection between blueberries and health outcomes, recommending moderate blueberry intake is a no brainer because of their likely health benefits, safety, and of course, their delicious taste.

Blueberries growing on the vine

Blueberries are native to North America, and if you’re lucky enough to live in or visit an area where they grow wild, take advantage of picking them fresh. As the berries form, they are a bright green (hello chlorophyll!). As they ripen, the chlorophyll degrades and the berries turn white to pink to red, then finally blue as anthocyanin and sugar production increases.

Anthocyanins aren’t the only molecules that give plants purple hues. Betalains are another class of compounds that impart this color. Let’s take a look at how they compare.

Anthocyanins vs Betalains

The function of these two sets of molecules in plants is the same – to provide color to attract pollinators and to protect them from environmental stress. Interestingly, you won’t find both molecules in the same plant, and scientists haven’t figured out exactly why.

It appears that plants use either the synthesis pathway to anthocyanins or to betalains, but not both. Most plants produce anthocyanins, as that seems to be the most energetically favorable route for antioxidant protection. However, many plants of the order Caryophyllales produce betalains instead.

Ornamental plants with betalains include:

  • Cacti
  • Four O’clocks
  • Ice Plant
  • Globe Amaranth
  • Bougainvillea

Purple amaranth buds

Many Caryophyllales are adapted to life in harsh conditions, such as drought and high salt conditions, so it is speculated that betalains evolved to help plants manage in these environments.

Structurally, anthocyanins and betalains contain conjugated double bonds that allow them to absorb certain wavelengths and reflect others, which gives them their color, and they are both water-soluble. The main difference between them, however, is that betalains contain nitrogen while anthocyanins do not.

In addition, betalains’ color is more stable, which is why these molecules are often used as food colorants. Let’s take a closer look at these compounds.

All about the Betalains

Tyrosine, an amino acid and source of nitrogen, is the precursor to the production of betalains. Betalains come in two types and colors:

  • Betacyanins – red/violet
  • Betaxanthins – yellow/orange

Like anthocyanins, betalains are named after the species where they were discovered so their names, such as betanin, amaranthin, gomphrenin, and bougainvillein, are recognizable.

Foods containing betalains include:

  • Beets
  • Amaranth
  • Rhubarb
  • Swiss Chard
  • Quinoa
  • Spinach
  • Prickly pear
  • Dragonfruit

Like the other nutrients of the rainbow, betalains are great antioxidants, perhaps even stronger in this ability than the anthocyanins. This feature, plus their anti-inflammatory nature, also makes them an ideal research subject for potential therapeutic application for a variety of conditions such as cardiovascular disease, cancer, and diabetes.

Furthermore, betalains exhibit antimicrobial properties. Scientists propose that betalains may interfere with the cell membranes of microbes, ultimately leading to their demise. Amaranth, for example, is particularly effective against malaria.

Although betalains are pretty amazing molecules, it’s important to consider the presence of other nutrients and phytochemicals in these plants, such as polyphenols, for their antimicrobial contributions as well.

Red beets on a wooden table


When I think of purple foods, beets immediately come to mind, thanks to the high betalain concentration, particularly betacyanins. The nutritional profile of beets is also impressive. Beets are a great source of:

  • Fiber
  • Folate
  • Manganese
  • Copper
  • Potassium
  • Iron
  • Vitamin C
  • Nitrates

In addition, beet greens are a great source of carotenoids, such as lutein, so seek out the entire plant when you can.

Nitrates are particularly interesting nutrients found abundantly in beets, as well as dark leafy greens. In the body, they convert to nitric oxide, which dilates blood vessels and improves blood flow, with potential benefits that include lowering blood pressure and improving muscle function.

Peeling and chopping beets stains my fingers and cutting board a beautiful magenta purple. For some people, beet consumption can also cause discoloration of urine and feces, an alarming, yet harmless phenomenon called beeturia.


Beeturia, or more technically, betacyaniuria, is the condition of pink or red urine or feces following consumption of foods rich in betalains, particularly betacyanins found in beets. It affects roughly 10-15% of the population, with increased prevalence among those with iron deficiency or malabsorption issues.

If iron deficiency is suspected, ask your doctor to order simple blood tests to confirm the condition.

Though the condition may be disconcerting, it is considered harmless. Check out this hilarious Portlandia sketch, and don’t worry, it’s just beets.

Beet Kvass

There are many ways to enjoy beets – roasted, steamed, pickled, eaten raw like carrot sticks, or in salads and soups. I really like this lightly fermented beet drink, taken from Sally Fallon’s Nourishing Traditions.


  • 2-3 cups of peeled and diced beets – about ½ inch cubes (about 2-3 medium to large beets)
  • ¼ cup whey (liquid remaining from strained, plain yogurt)
  • 1 tablespoon sea salt
  • Water
  • Additional flavorings such as ginger or lemon zest can be added if desired


Combine all ingredients in a two-quart glass jar, or divide it equally into quart-sized jars. Fill with water leaving an inch of headspace. Cover and leave at room temperature for about two days, then transfer to the refrigerator. Strain a portion to drink (Ms. Fallon recommends 4 ounces in the morning and at night) or use in salad dressing or soup.

When a small amount of liquid remains, you can refill the jar with water once more and leave it at room temperature an additional two days to make a more diluted tonic. Discard the beets after the second brewing.

If whey is unavailable or you desire to make this recipe vegan, simply omit the whey. You may need to leave the mixture at room temperature for longer to achieve desired fermentation. The mixture should be dark purple and slightly effervescent.

The Colors of the Rainbow are Everywhere

I hope you enjoyed learning about the molecules responsible for the colors of the flowers, leaves, and foods around you. The variety and beauty of these colors is not only a delight to the senses, but nourishment and antioxidant protection for ourselves, animals, pollinators, and plants. Get creative and include a variety of colors on your plate every day!


About the author

Karyn Lane is working towards her holistic nutrition certification in NTI’s Nutrition Therapist Master Program. She finds her chemistry degree a useful tool in her study of holistic nutrition and loves to treat herself as a laboratory for new recipes and cooking techniques. You can follow her on Instagram @feel.alive.nourishment.

About Nutrition Therapy Institute’s Holistic Nutrition Certification

Nutrition Therapy Institute (NTI) is a leader in holistic nutrition education. Since 1999, NTI has provided students with the highest quality in nutrition training by offering comprehensive holistic nutrition courses online and in-person to help students achieve thriving careers as holistic nutrition therapists in the field of holistic nutrition counseling and wellness. Interested in starting our holistic nutrition courses and earning your holistic nutrition certification? Attend an informational webinar to learn more by signing up HERE.  


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