You may have heard rules of thumb about nutrition lauding color: “Eat the rainbow” or “The more colorful the food on your plate, the more nutrients.”

That’s because of flavonoids, complex chemical compounds that give most fruits, vegetables and spices their colors.

Or maybe you’ve heard about antioxidants, but never knew what they were. Vitamin C and vitamin E are important antioxidants and so are flavonoids. Antioxidants help defend your cells from unstable molecules called free radicals. When free radicals build up, heart disease, type 2 diabetes, cancer and other illnesses are all more likely and more dangerous.

Let’s look at type 2 diabetes. One meta-analysis grouped results of eight studies, covering more than 312,000 volunteers in all, over periods from four to 28 years. The risk of type 2 diabetes dropped by five percent for each 300mg a day increment of daily flavonoid consumption (Xu et al, 2018).

If you do have diabetes, eating flavonoids may help minimize the damage. For example, one study offered men with type 2 diabetes hamburger—or hamburger with a mix of the flavonoid-rich spices rosemary, garlic, ginger, black pepper and oregano. The spice-hamburger group had significantly better scores on measures of vascular function two hours later (Li et al., 2013).

Rainbow composition with fresh fruits and vegetables on white background
It is indeed possible – and enjoyable! – to “eat the rainbow.”

So spice up your hamburger! Also add a salad and raw fruit for dessert. You’ll get the most flavonoids if you eat your fruits and vegetables raw and fresh, before the colors fade, and eat the skin, where the flavonoids often concentrate (Premkumar, 2014). Some spices, however, are exceptions to the fresh-is-better rule. Dried parsley is more powerful than fresh (Janabi et al., 2020).

Sadly, only one in ten American adults gets enough fruits or vegetables, according to the Centers for Disease Control. You want to be one of that happy group: Aim for three cups a day of a variety of vegetables and at least one and a half cups of fruit (CDC, 2017).

That’s along with your seafood, of course, which has plenty of its own unique benefits.

Know Your Flavonoids

If you want to go beyond simply remembering to eat colorful raw fresh salads, things quickly get complex. There are more than 8,000 flavonoids, falling into six groups based on their chemical structure, and each has its own benefits.

Ideally, most days or weeks you’ll get enough of each subgroup, briefly explained below. There are exceptions to the color groups mentioned in parentheses, but they can give you a general idea of what to seek.

Flavones (Blue and White)

This group colors blue and white flowering plants. They’re notable for delaying the rate at which your body absorbs drugs. Dried parsley is a top source (Janabi et al., 2020). Chamomile and peppermint tea contain flavones.

The flavone you may have heard of is luteolin, which is both an anti-histamine, good for the heart and under study for multiple benefits. There is early evidence, for example, that it may help improve the behavior of some children with autism spectrum disorder by cutting inflammation (Luo et al., 2017; Tsioloni, 2015). Radicchio, green peppers, lemon, spinach and broccoli are high in luteolin (Bender, 2018).

Anthocyanidins (Red, Dark Red, Brown)

These compounds may help you avoid obesity and diabetes by delaying the absorption of carbohydrates and lowering blood sugar levels after meals ( Solverson, 2020). Elderberry, chickpeas, red berries and pecans are top sources (Janabi et al., 2020).

Flavanones (Green, Orange, Yellow, Light Green)

Find these in dried oregano, citrus fruit and artichokes, where they can help you relax and protect your heart (Janabi et al., 2020).

Isoflavones (Green)

Plentiful in soy, these compounds may mimic estrogen, and possibly affect the risk of menopausal symptoms. Some nutritionists recommend against soy if you’re worried about breast cancer, but the research is not clear at the moment (Janabi et al., 2020).

Flavonols (Green, Purple, Red)

This subgroup includes quercetin, an antihistamine that can help tame allergy symptoms and other inflammatory issues, while providing other antioxidant benefits. Capers and red onion are concentrated sources (but don’t let your onions sit around for more than a week or so, as quercetin degrades over time). Top fruit sources are Goji berries, red apples and cherries (Janabi et al., 2020).

Flavanols (also called flavan-3-ols, to avoid confusion with nearly identically named flavonals) (Brown, Green, Black, Peach, Red, Yellow)

Rainbow composition with fresh fruits and vegetables on white background
Green tea is rich in a flavanol called EGCG epigallocatechin-3-gallate, better known as EGCG, as well as other flavanols including catechin, epicatechin gallate, and epicatechin.

Top sources are green and black tea, dark chocolate and blackberries (Janabi et al., 2020). Green tea especially offers a kind of flavanol called catechin that may boost heart and neurological health. Flavanols in onions, kale, peaches, berries, tomato and broccoli may help manage the symptoms of heart disease.

If you want to be sure you’ve gotten all six kinds of flavonoids in a day, eat blueberries. Blackberries, strawberries and cherries also contain all six.

If you’re concerned about a particular illness, here’s a crib sheet. Remember that these are not cures. Research has linked eating these foods with a lower risk of the illness or milder or less frequent symptoms (Janabi et al., 2020).

  • For diabetes, coffee, green tea, berries, apple, and onion have some research supporting them as helpful.
  • For heart disease, apple, black tea, garlic, cabbage, and citrus may help.
  • For prostate cancer, the same is true for tomato, cauliflower, and broccoli.
  • For cancer generally, garlic, soybeans, cabbage, ginger, carrots, celery, cilantro, parsley and parsnips are high on the list (Janabi, et al., 2020).
  • For allergies or histamine-intolerance, consider splurging on radicchio and capers, if you like them.

What about supplements?

You will seldom go wrong seeking out nutrients from whole foods rather than supplements, as some versions have risks. For example, a high dose of green tea extract has been linked to thyroid damage and goiters (Egert and Rimbach, 2011).

So we return to the general rule – eat the rainbow. In other words, eat a variety of brightly colored fruits and vegetables. Variety is your friend!