author: Dr. Kevin Curran
What are phytochemicals?
Phytochemicals are chemicals that are found within plants. Its that simple. The prefix ‘phyto‘ means plant.
Plants naturally produce these chemicals because the phytochemicals provide a benefit to the plant. For example, phytochemicals often protect the plant from UV radiation from the sun, help the plant defend against bacteria infections and provide the plant with color.
When we eat plants, these phytochemicals are then transferred to our bodies. Research demonstrates that phytochemicals can influence and enhance certain biological pathways in our body. This is why it is so important to include a wide variety of fruits and vegetables in your diet.
The words phytochemical and phytonutrient are often used interchangeably. The words have similar meanings, however it is important to remember that phytochemicals are not considered essential nutrients. Carbohydrates, vitamins, proteins and minerals are examples of essential nutrients. This means our body relies on these molecules to stay alive. As far as we know, phytochemicals are not necessary to stay alive. Therefore, we need to be patient and examine the science before making bold health claims.
Phytochemical research is a new avenue within nutritional science. Scientists are actively exploring the health benefits of many phytochemicals. I’ll be following along with this research and sharing the results with you.
This page serves as a Phytochemical 101.
I’ll explain the basics of this new avenue in nutritional science. I’ll also keep the page updated to reflect new research on this exciting subject.
photo: Spmallare, CC BY 3.0, via Wikimedia Commons
The new food nutrition pyramid illustrates the emphasis on fruits and veggies that are packed with phytochemicals.
How do phytochemicals work?
There are many different phytochemicals and each works in a unique manner within the cells of our body. Below, I list a few general ways that phytochemicals engage with our body.
- Antioxidant: Many phytochemicals have antioxidant activity. This means these chemicals can protect our cells against the oxidative damage associated with free radicals and other high energy molecules. It is thought that antioxidant activity will help reduce the effects of aging and possibly help prevent certain diseases.
- Stimulation of enzymes: By altering the activity of our body’s natural enzymes, phytochemical could help reduce certain health risks. Indoles, found in cabbages, stimulate enzymes that make estrogen less effective. This enzymatic inhibition could reduce the risk for breast cancer.
- Anti-bacterial effect: The phytochemical allicin from garlic has demonstrated anti-bacterial properties.
- Stimulate our immune system: Many phytochemicals regulate the manner that the cells of our immune system communicate with each other.
- Reduce inflammation: Eating certain plants can decrease inflammatory factors or increase anti-inflammatory factors.
How do you add phytochemicals to your diet?
This part is simple.
Eat meals that contain a wide variety of vegetables, fruits, whole grains and legumes. If you maintain a healthy diet, you probably already include these plants in your meals. Colorful fruits and vegetables tend to be the best source of phytochemicals.
In the table below, I summarize the major phytochemical groups. After the table, I dive into more detail and research for each of the groups.
||Prominent examples||Common food sources|
red, orange, green fruits; colorful vegetables
dark leafy greens; broccoli, carrots
anthocyanidins, flavan-3-ols, flavonols,
flavanones, flavones, isoflavones,
citrus fruit, berries, red wine, tea
apples, black elderberry, legumes
|Glucosinolates||sulforaphane, indole-3-carbinol, isothiocyanates||
(broccoli, kale, brussel sprouts, cabbage, ext.)
β-sitosterol, campesterol and stigmasterol
unrefined vegetable oils,
whole grains, legumes, nuts, seeds
lignan, cellulose, β-glucans,
psyllium seed husks, oats, legumes,
chia seeds, flax seeds, artichoke
Carotenoids are plant pigments. Pigments add color to plants. The carotenoid pigments are responsible for creating the yellow, orange, and red color of many fruits and vegetables. Of the thousands of carotenoids, beta-carotene is probably the most popular. Beta-carotene gives carrots, pumpkins, and sweet potatoes their rich orange color. After we eat plants with beta-carotene, our body converts beta-carotene into Vitamin A.
Observational studies suggest that people who consume a diet that is high in carotenoids will experience a lower chance of acquiring cardiovascular disease and some cancers (i.e. lung cancer). You can read more about these results from this meta-analysis review.
Observational studies also suggest that diets rich in other carotenoids (lutein and zeaxanthin) can help slow the development of age-related macular degeneration (AMD). Here are more details on this AMD meta-review.
Important sidenote: When reviewing the scientific literature on the health benefits of eating plants enriched for phytochemicals, it is important to be mindful of covariance. Covariance is the measure of the joint variability of two seemingly random variables. For example, the type of people who eat a lot of brightly colored plants are also more likely to exercise and to refrain from smoking cigarettes.
In other words, if you eat a lot of carrots you probably also do other healthy things.
From the scientist’s perspective, it is difficult to know if an observed decrease in cancer rate is associated with the carotenoids or the overall healthier lifestyle. In summary, you need to aware of the different types of clinical trials. Observational studies are not the ideal way to explore the health benefits of specific phytochemicals.
Flavonoids are a large family of over 5,000 chemical compounds that carry out important functions in plants. Flavonoids are used by plants to attract pollinators, regulate cell growth and combat environmental challenges (microbial infection, UV radiation, viral infection, ext.)
The chemical structure of flavonoids is polyphenolic. This means the structure contains many circular phenol groups. Much has been made about the antioxidant capacity of flavonoids, however it remains unclear exactly how much antioxidant activity is acquired after eating flavonoid rich foods.
Flavonoids do reveal strong antioxidant capacity in test tube experiments. However, bio-availability is a major concern for all beneficial dietary molecules. It seems that the flavonoids with the highest anti-oxidant capacity may be metabolized before entering into our cells. Read more about this here.
On a related note, we are just beginning to understand the effect that our microbiome has on the bioavailability of dietary nutritional molecules. Scientists are observing that our microbiome certainly effects our body’s ability to absorb beneficial flavonoid chemicals. You can read this paper for more insight into this phenomena.
It seems that the primary contribution of flavonoids comes from their ability to modulate cell signalling pathways. Altering a cell signalling pathway demands a much lower flavonoid concentration than would be necessary to exert an antioxidant effect. Therefore, in general, any reduction in flavonoid bio-availability would not be an issue in terms of cell signaling pathways.
By altering cell signalling pathways, flavonoids have been observed to produce anti-cancer, anti-diabetic, anti-inflammatory and neuroprotective properties. Much of this work has been performed in cell culture and in animal model systems, however the results are intriguing.
Multiple studies reveal how dietary flavonoids can reduce inflammation. This paper used apples as a source of flavonoids. This other paper used darkly pigmented berries (blueberry, blackberry and black currant) to demonstrate a decrease in inflammation.
Flavonoids seem to have the ability to impede the digestion and the absorption of sugars and carbohydrates. You can review this topic here. Additional work describes how flavonoids can improve insulin secretion.
Several studies explore the relationship between dietary flavonoid intake and cardiovascular disease. A 2014 meta-analysis revealed that higher dietary intakes of many of the flavonoid groups can significantly lower the risk of cardiovascular problems.
Sidenote: Anthocyanidins with one or more sugar groups attached are called anthocyanins.
Glucosinolates are a group of organic chemicals that contain sulfur and nitrogen. These phytochemicals occur naturally in the cruciferous family of plants. The cruciferous plants are incredibly popular, they include broccoli, cabbage, brussel sprouts, cauliflower and kale. Glucosinolates compounds are also found in watercress, horseradish, radishes, capers, kohlrabi and cress.
There are many different kind of glucosinolates, but sulforaphane, indole 3 carbinol and isothiocyanates are the most well studied in terms of their health benefits.
When we eat cruciferous vegetables, these glucosinolates are broken down into their active forms within our body. It is these partially metabolized chemicals (indoles and isothiocyanates) that are actually bio-active in our body. In fact, our own healthy gut bacteria helps break down these chemicals into their active form.
Multiple scientific reports demonstrate that eating high levels of cruciferous vegetables is associated with the reduced risk of several types of cancer. You can read more about these reports here.
A recent intervention study asked whether eating cruciferous vegetables could help your body detox from harmful chemicals. A trial of 391 healthy Chinese adults found that daily consumption of broccoli and cress can increase the amount of carcinogens purged from the human body.
The latest Dietary Guidelines for Americans encourages adults to eat 1-2 cups of dark-green vegetables per week.
Make sure to include lots of cruciferous veggies in this weekly serving of dark-green veggies!
Sidenote: You may ask yourself….
Why would a broccoli plant produce a chemical that delivers a health benefit to humans?
That’s a great question! The broccoli plant actually doesn’t care about human diet. Broccoli only cares about broccoli. The glucosinolate chemicals exist in these plants because they help the plants defend against insects and infections. Its just good fortune for us humans that these chemicals are also beneficial in our body once we eat the plant.
Phytosterols are cholesterol compounds that are naturally produced in plants. The best sources of phytosterols are whole grains, nuts, seeds and beans.
So… why do we care about phytosterols? Multiple reports conclude that consuming a diet rich in phytosterols will help lower our LDL cholesterol levels. If you remember….we want our LDL levels to be low and we want our HDL levels to be high. LDL stands for low density lipoprotein. It seems that a diet that includes 2 grams of phytosterols per day can lower LDL cholesterol levels by about 10%. According to this meta-analysis, it’s best to take these phytosterols with other food throughout the day, as opposed to once each morning as a supplement.
In terms of chemical structure, phytosterols feature a double bond in a sterol ring. The most commonly consumed phytosterols are: stigmasterol, campesterol and beta-sitosterol.
Fiber is another important component of a balanced and healthy diet. I’ve previously written about the manner that fiber helps humans in regards to heart issues, diabetes and cholesterol levels. There are also definite connections between a high fiber diet and reductions in gastro-intestinal issues. For example, irritable bowel syndrome and hemorrhoids both seem to be greatly reduced once you shift to a high fiber diet. That has certainly been my experience. My physician told me to aim for 25-30 grams of fiber daily. I am now in the habit of drinking a smoothie of chia seeds and pysllium husk. I also add lots of fruits and flax seeds to my morning cereal. That combined with a salad gets me pretty close to 25 grams.
When we talk about fiber, we are referring to a collection of large biological molecules. Lignans, cellulose, hemi-cellulose are all considered fiber. These molecules make up the rigid cell wall in plant cells. When we eat seeds, fruits and veggies, we then consume those building blocks of the plant cell.
Eat more garlic! Your breath will suffer but your body will thank you. Garlic (Allium sativum) is a plant with a large, bulbous root. Above the ground, garlic looks like grass. This species is closely related to the onion, the shallot, the leek and the chive.
Garlic is native to Central Asia and has been used by humans for thousands of years. The ancient Egyptians used garlic as both a food seasoning and as a traditional medicine.
Garlic is packed full of organosulfur chemical compounds. Multiple preclinical studies suggest these organosulfur chemicals offer various health benefits: antioxidant, anti-inflammatory, antimicrobial and cardio-protective ability. In terms of the inflammatory effect, it is thought that these organosulfur chemicals can inhibit elements of our body’s inflammatory response. These elements include enzymes like COX (cyclooxygenase), cytokine, iNOS (inducible nitric oxide synthase) and LOX (lipoxygenase). Yes, I realize that’s a mouthful…if you would like to read more, this article is a good place to start.
When we chop and crush garlic, we’re activating a garlic enzyme called alliinase. This plant enzyme converts S-allyl-L-cysteine sulfoxide into allicin. Allicin then breaks down into many different organosulfur compounds in our body. Long story short, by preparing fresh garlic cloves for our dinner, we start the process of activating the beneficial organosulfur compounds found in garlic.
To read more scientific reports exploring the health properties of garlic, please visit this garlic page on the Linus Pauling Institute website.