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  • Writer's pictureCathy Dyer

Why Eating the Rainbow Matters

A real honest discussion about phytochemicals.

Diverse colors in your diet provide the vitamins, minerals, and (possibly) healthful phytochemicals your body needs.


Did I say something-or-other chemicals? Yes I did. I am a chemist, after all. A chemical is any substance consisting of matter, whether a pure element or a mixture making a compound, solution, or gas.

Phytochemicals are naturally occurring chemicals produced by metabolism in plants to aid their growth or their protection from predators, pathogens, or competitors. They provide fruits and vegetables with aroma, flavor, and color.

Phytochemicals are undergoing a great deal of research to determine whether or not they provide positive health outcomes for the humans who eat them, often with promising even if inconclusive results. Sorry to be a buzzkill about it, but real nutrition science takes patience and lots and lots of experiments, observations, and statistical analysis conducted over a meaningful period of time before human health benefits can be attributed to molecules.

Tens of thousands of phytochemicals have been discovered, and there will likely be thousands more discovered in the future. To give you an idea how vast this area of research is, just take a look at this chart of dietary phytochemical classifications.

The next time someone tells you a food is packed with phytonutrients, ask them "Yeah, which ones? And what do they do?"

Some people use the word phytonutrients instead of phytochemicals, but the fact is the jury is still out on whether or not phytochemicals are essential nutrients and whether or not they all provide health benefits. A nutrient is a food component that nourishes the body to provide growth, maintenance, and repair. For example, fiber is an important part of your diet, yet fiber is not classified as an essential nutrient.

I'm making this important distinction between the words phytonutrient and phytochemical because there is so much pseudoscience published as bonafide health advice it is easy for any reader to believe something has already been proven when it hasn't.

Science based websites and other sources are careful when discussing phytochemicals. The American Institute for Cancer Research has a chart listing all the health benefits phytochemicals "may" provide and talks about the "potential" benefits provided by phytochemicals. You should always be on the lookout for these types of subtle disclaimers when reading nutrition information.

There is no conclusive evidence regarding health benefits derived from eating phytochemicals. The only exception is the carotenoid beta-carotene which is converted to vitamin A in the body. Food and supplement labels are regulated by the FDA. The FDA does not allow food and supplement labels to make claims of phytochemical health benefits because they are not yet proven. Chapter 21 of the Code of Federal Regulations Chapter 1 Part 101.14 (21 CFR 101.14) explains the regulations for food and supplement health claims. Subpart E lists specific approved health claims. Spoiler alert: health claims about phytochemicals and antioxidants are not part of the approved list - except for beta-carotene.

Books and websites, etc. are protected as "free speech" and therefore, do not have to actually have scientific data to back up their claims about the health benefits of phytochemicals, or crazy trendy diets, or any other nutritional ideas they are selling. Just keep this in mind when you read nutrition related articles extolling the benefits of latest fad phytonutrient. Look for references from reliable, peer reviewed scientific journals and then read those published papers with a very critical eye.

What Do Fruit and Vegetable Colors Tell You?

Fruits and vegetables have five color categories: Red, blue/purple, orange/yellow, green, and white/brown based on phytochemicals acting as pigments.

RED fruits and vegetables may get their red color from the carotenoid lycopene, which is an antioxidant some believe reduces the risk of cancer and promotes heart health. Red fruits and vegetables may also contain one or more flavonoids in the anthocyanin category, which some have also claimed promote heart health and reduce the risk of cancer.

BLUE/PURPLE color is also caused by flavonoids in the anthocyanin category, which may protect cells from damage by reducing inflammation, and may also reduce the risk of cancer, stroke, and heart disease.

ORANGE/YELLOW fruits and vegetables contain one or more of the 600 known naturally occurring carotenoids. The carotenoid Beta-carotene found in carrots, sweet potatoes, and pumpkins is converted to vitamin A in your body. Vitamin A does provide health benefits to eyes and mucus membranes. Lutein is another carotenoid antioxidant found in orange/yellow fruits and vegetables, but even more so in dark, leafy green vegetables. You are born with lutein in your eyes. It is believed lutein protects the eye by filtering damaging blue light and by preventing cataracts and macular degeneration. Zeaxanthin has the same chemical formula as lutein, but the atoms are arranged differently. Zeaxanthin may also play a role in eye health. It is hard for scientists to figure out the roles lutein and zeaxanthin play, because generally where one of these molecules is present, so is the other, so figuring out which is doing what isn't easy and is still under investigation.

See how they are almost the same, but not quite?

GREEN colored fruits and vegetables can contain carotenoids, indoles, glucosinolates, lutein, zeaxanthin, isothiocyanates, and obviously chlorophylls. Glucosinolates are organosulfur compounds containing sulfur (duh), and produce the distinctive bitter taste found in cruciferous vegetables such as cabbage, broccoli, collard greens, kale, Brussels sprouts, and capers. There is a great deal of research currently in process to determine whether glucosinolates reduce the risk of cancer.

BROWN/WHITE is a fruit and vegetable color category, but obviously not colors of the rainbow, but just run with this thing, ok? Cruciferous vegetables contain the organosulfur compound sulforaphane. Allicin is found in garlic and quercetin is a flavonoid found in white vegetables such as onions and leeks. There are various health claims associated with the phytochemicals in brown and white colored fruits and vegetables.

Any single fruit or vegetable can contain literally thousands of different phytochemicals.

The main health benefits nutrition hucksters try to link to phytochemicals are that they reduce the risk of cancer and promote heart health. In fact, if you google search ANY phytochemical you will likely find articles claiming it reduces the risk of cancer. This is because many phytochemicals are antioxidants, and act as antioxidants in plants and test-tubes, but there isn't any real evidence they act as antioxidants in the human body. None. Readers beware.

A critical review of the scientific data leads to the conclusion that the color of fruits and vegetables only reveals which phytochemicals are acting as pigments in the foods. Health claims about phytochemicals are speculative and based on research that is not yet conclusive.

Why Eating the Rainbow Is Still a Worthwhile Strategy

Let's focus on vitamins and minerals.

The roles of vitamins and minerals in promoting human health are also still undergoing a great deal of research, and different vitamins and minerals have become trendy through the ages. Right now vitamin D is very popular in articles, and all sorts of unsubstantiated claims about vitamin D are being pushed as nutrition gospel on the unsuspecting public. Vitamins A, C, and E have had their day in the sun, too.

All fads and hoopla aside, there are scientifically established health benefits related to all the essential vitamins and minerals. The best resource for you to learn about those health benefits is this book, which you can download for free.

The single best way you can ensure you and your family get all the required vitamins and minerals to promote optimal health is to get adequate exposure sunlight (for vitamin D) and eat a balanced diet including a variety of fruits and vegetables of various colors. This graphic designed by Russell van Kraayenburg of Chasing Delicious is a fantastic fruit and vegetable guide.

Eating the Rainbow is a worthwhile approach towards getting all the vitamins and minerals needed for optimal health - no knowledge of phytochemicals required.


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