Without these chemicals in plants, hot peppers wouldn’t have their zing, Brussels sprouts wouldn’t be bitter, and blueberries wouldn’t be blue. What are they? They’re phytochemicals. These plant (ie, “phyto”) chemicals are found in all kinds of fruits, veggies, whole grains, nuts, seeds, and legumes. They give these natural goodies their aroma, color, and smell—and they offer a kaleidoscope of health benefits.
Research is just emerging about the importance of phytochemicals in the diet, with more than 5,000 extant. So far, the findings on their impact on human health have been largely positive. Here is a look at five examples of phytochemicals that can offer an array of health benefits, based on the research.
Carotenoids are red, orange, yellow, and green pigments found in most fruits and veggies. Humans cannot synthesize these compounds and must consume them either as part of a healthy diet or via supplementation.
Carotenoids function most notably as antioxidants, but individual types of carotenoids have specific actions. For example, lutein and zeaxanthin form macular pigment in the eye, and β-carotene has a pro-vitamin A function.
“The benefit of lutein in reducing progression of age-related macular eye disease and cataracts is strengthening,” wrote the authors of a review article published in Archives of Biochemistry and Biophysics. “An intake recommendation would help to generate awareness in the general population to have an adequate intake of lutein rich foods. There is evidence that carotenoids, in addition to beneficial effects on eye health, also produce improvements in cognitive function and cardiovascular health, and may help to prevent some types of cancer.”
Isothiocyanates (ITCs) are phytochemicals found in cruciferous vegetables, such as garden cress and broccoli. ITCs are stored as thioglucoside conjugates (ie, glucosinolates) in cruciferous veggies. Cutting or chewing these glucosinolates results in physical plant tissue damage that releases an enzyme called myrosinase, which converts glucosinolates to ITCs. Furthermore, intestinal microflora can generate ITCs.
Preclinical and observational studies support a preventive role for ITCs in cancer. Naturally occurring ITCs can cause selective growth arrest and cell death of cancer cells.
“Existing mechanistic paradigm stipulates that ITCs may not only prevent cancer initiation by altering carcinogen metabolism but also inhibit post-initiation cancer development by suppressing many processes relevant to tumor progression, including cellular proliferation, neoangiogenesis, epithelial-mesenchymal transition, and self-renewal of cancer stem cells,” wrote the authors of a review article published in Carcinogenesis. “Moreover, the ITCs are known to suppress diverse oncogenic signaling pathways often hyperactive in human cancers (eg, nuclear factor-κB, hormone receptors, signal transducer and activator of transcription 3) to elicit cancer chemopreventive response.”
Flavonoids are found in apples, berries, oranges, onions, and various other fruits and vegetables. They are formed from the essential amino acid phenylalanine and imbue the flowering portions of plants with vibrant colors.
Flavonoids have strong antioxidant properties and are radical scavengers. In humans, they promote the protection of enzyme systems. Observational studies indicate that they also protect against heart disease, cancers, and age-related diseases.
Some flavonoids polymerize to form tannins, which are secondary plant metabolites that can be hydrolyzed or condensed. Condensed tannins are referred to as proanthocyanidins.
Proanthocyanidins are found in flowers, nuts, fruits, bark, and seeds of plants, where their astringent properties ward off pathogens and predators. Rich, fruit sources of proanthocyanidins include cranberry, lingonberry, black elderberry, black chokeberry, black currant, blueberry, persimmon, banana, pomegranate, plum, and apricot. They enrich these fruits with aroma, astringency, bitterness, color, sourness, and sweetness.
“Proanthocyanidins have a wide range of health beneficial properties,” wrote the authors of a review article published in Biomedicine & Pharmacotherapy. “Antioxidant, antitumor and immunostimulating properties of these compounds have come forth. Studies have shown that proanthocyanidins help to protect the body from sun damage, to improve vision, to improve flexibility in joints, arteries, and body tissues such as the heart, and to improve blood circulation by strengthening capillaries, arteries, and veins.”
Furthermore, the authors noted that oligomeric proanthocyanidin complexes (OPCs)—molecular complexes of phytochemicals—harbor antioxidant, antibacterial, antiviral, anticarcinogenic, anti-inflammatory, anti-allergic, and vasodilatory actions. OPCs can mitigate lipid peroxidation, platelet aggregation, and capillary hyperpermeability. Additionally, they can exert effects on apoptosis, gene expression, and transcription factors such as NF-kB.
Quercetin is a flavanol antioxidant present in apples, berries, onions, and citrus fruits. It’s linked to lower rates of heart disease and stroke.
In a low-powered, randomized, double-blinded, placebo-controlled, crossover trial, researchers enrolled male and female participants with prehypertension (n = 19) and stage 1 hypertension (n = 22) to examine the efficacy of 730-mg quercetin daily for 28 days vs placebo. Specifically, researchers examined the quercetin’s effects on both hypertension and biomarkers of oxidative stress.
They found that although blood pressure levels were not affected in prehypertensive patients, they dropped in patients with stage 1 hypertension (P < 0.01): systolic (-7 +/- 2 mmHg), diastolic (-5 +/- 2 mmHg), and mean arterial pressures (-5 +/- 2 mmHg). Unlike in animal models, though, markers of oxidant stress measured in the plasma and urine were unaffected by the quercetin intervention.
Harnessing the power of phytochemicals
With so many phytochemicals out there, you may be wondering how to garner their full benefit. Good news: Many fruits and veggies contain numerous different types of phytochemicals, which complement each other to contribute to overall health. For instance, a carrot contains more than 100 phytochemicals.
One surefire way to consume as many phytochemicals as possible is to look for a diversity of colors in the fruits, vegetables, seeds, legumes, and nuts you eat. A variety of color indicates that you are consuming different types of phytochemicals in your diet. For instance, as part of the 5-9 servings of fruits and veggies you are recommended to eat each day, try making a salad replete with broccoli, tomatoes, carrots, peppers, apples, walnuts, and berries, and grapes. This colorful concoction will not only benefit your body but also color your plate and please your palate. Just remember to drizzle—not douse—with the salad dressing.