The Colourful World of Phytochemicals

Phytochemicals are a hot topic right now. You’ll hear them called polyphenols, phytonutrients or bioactive compounds. No matter the term, you’ve probably come across them. Yet, these 50,000 or more compounds have recently been described as the “dark matter of nutrition”. They are said to be largely invisible to the public. So, what do we actually mean when we talk about phytochemicals? And why do they matter?

Phytochemicals, polyphenols or bioactive compounds?

Not so clear-cut: Many definitions are used to describe plant-derived compounds. Terms overlap and are used somewhat interchangeably. Generally, phytochemicals are described by their source, polyphenols by their chemical structure and bioactives and phytonutrients by their biological activities. (Frank et al. 2019)

1. Bioactive compounds are broadly defined as having demonstrated activity in biological systems, without specifying whether the activity is beneficial or harmful. They include chemicals from plants and animal-derived components.
2. Phytochemicals is the umbrella term to describe compounds produced by plants.
3. Phytonutrients are phytochemicals that exert health-beneficial effects, demonstrated in animal or human trials.
4. Polyphenols are a group of phytochemicals, based on their chemical structure.

The term “chemical” can be confusing: Using the term chemical in a health setting goes against some of the ideas we may have about chemicals, i.e. that they must be bad. There is often confusion about what a “chemical” actually is. But chemicals are essential building blocks for all matter, including people, animals and plants. They are not inherently bad or good.

5 things to know about phytochemicals

1. Phytochemicals are compounds produced by plants

Plants produce phytochemicals in small amounts to help them survive in their environment, mainly because they can’t outrun their predators. They are secondary metabolites – meaning that they are not essential for the plant’s basic functions but give them an advantage in their environment, including colours, scents and various defensive activities. Plants contain a remarkable chemical diversity with most containing around 2,000 chemicals. Yet, 85% of these chemicals remain unquantified. (Barabási et al. 2020)

2. Phytochemicals are grouped by chemical structure, ie. the way the molecule is shaped

There are a wide range of phytochemicals out there, but well-known groups include:

• Phenolics, such as anthocyanins, flavonoids, stilbenes, lignans, and phenolic acids
• Organosulfur compounds, such as isothiocyanates and indoles
• Terpenoids, such as carotenoids
• Alkaloids, such as theobromine and synephrine
• Phytosterols, such as stigmasterol and sitosterol

Plus many more! These groups are further subdivided into specific types of compounds. For example, lycopene, lutein and zeaxanthin are all carotenoids. Tens of thousands of phytochemicals exist, but only a small number have been isolated and identified from plants. There are still many more to be discovered.

3. Many phytochemicals play a role in health and disease

Regularly eating phytochemicals through plants may help reduce the risk of chronic diseases, such as type 2 diabetes, cardiovascular disease and several types of cancer, as shown by several human studies. More marginal evidence also suggests a potential role in preventing neurodegenerative diseases and mental health problems, such as depression. (Dingeo et al. 2020; Noruzi et al. 2022)

4. They may contribute to health through various pathways

Researchers propose a number of pathways through which phytochemicals can influence health, such as:

• By protecting cells: Phytochemicals may activate defensive cellular responses, such as autophagy, DNA repair and antioxidant enzyme expression to help protect cells and organs against damage and mutations.
• By regulating inflammation: Many phytochemicals exhibit anti-inflammatory effects via interacting with the transcription factor NF-κB, which is involved in the formation of pro-inflammatory cytokines like TNF-α and IL-1β.
• By modulating the gut microbiota: Phytochemicals that are not absorbed may also reach the gut microbiota and affect its composition and activity. They can serve as substrates for gut microbes, improve intestinal barrier function and reduce pathogenic species.
• Other potential effects: Many other potential mechanisms are suggested, such as reducing the absorption of cholesterol and bile acids.

Many are unknown: These are general mechanisms. The wide range of phytochemicals found in plants may act in various different ways and many of these are unknown. More research is needed to better understand the specific functions of different phytochemicals, their effects on human health and optimal amounts. We’re still just learning about them!

5. Climate change and farming practices affect the phytochemicals in our food

The amounts of phytochemicals produced by plants vary depending on various environmental factors, such as sunlight, soil quality and moisture. Modern agriculture practices not only affect the health of the planet but also the phytochemical content in our food. Why?

• Excessive focus on taste and yields: Plant breeding strategies focus almost exclusively on yield, disease resistance and taste —such as reduced bitterness and more sweetness. So, phytochemicals are often neglected in favour of carbohydrates proteins and fats.
• Harmful effects on the soil: Modern agriculture practices like the excessive use of monoculture and pesticides harm the development of healthy soil and plant microbiomes, influencing the natural development of a complex phytochemical milieu.
• Loss of plant species diversity: There has been a huge decrease in the diversity of species in the wild and within-species variety, which is likely to reduce phytochemical availability. (Fahey et al. 2021)

👉 To recap, 3 things to tell people about phytochemicals:

1. Beyond fibre, vitamins and minerals, plants also provide a remarkable variety of compounds that can contribute to health by activating our cells’ defence systems, regulating inflammation and modulating the gut microbiota.
2. Fruits and veggies have different colours and aromas because of the unique types and amounts of phytochemicals they contain, like carotenoids, and flavonoids. So mix it up with a diverse range of fruits, vegetables, nuts, beans and pulses.
3. Sustainable food production and environmental health are crucial to preserving these valuable compounds in the plants we eat.

Most people know about vitamins and minerals in food, but phytochemicals found in plants remain largely unknown. That’s why we started our # Seasonal Foods– to unveil some of the unknowns about food that don’t always reach outside academia. To learn more about the phytochemicals in various foods, subscribe to our Seasonal Sundays newsletter. Each week, we take a 360° look at food through its history, composition, cultivation and versatile uses in the kitchen. Join the conversation!

Papers to check out

Making sense of plant-derived compounds in nutrition research

Jan Frank, Naomi K Fukagawa, Anna R Bilia, Elizabeth J Johnson, Oran Kwon, Vish Prakash, Teruo Miyazawa, Michael N Clifford, Colin D Kay, Alan Crozier, John W Erdman, Jr, Andrew Shao, Gary Williamson, Terms and nomenclature used for plant-derived components in nutrition and related research: efforts toward harmonization, Nutrition Reviews, Volume 78, Issue 6, June 2020, Pages 451–458, https://doi.org/10.1093/nutrit/nuz081

Classes of phytochemicals & types of plants

Barbieri R, Coppo E, Marchese A, Daglia M, Sobarzo-Sánchez E, Nabavi SF, Nabavi SM. Phytochemicals for human disease: An update on plant-derived compounds antibacterial activity. Microbiological research. 2017 Mar 1;196:44-68.

Do phytochemicals belong on our plate for sustaining healthspan?

Fahey JW, Kensler TW. Phytochemicals: Do they belong on our plate for sustaining healthspan?. Food Frontiers. 2021 Sep;2(3):235-9.

The unmapped chemical complexity of our diet

Barabási AL, Menichetti G, Loscalzo J. The unmapped chemical complexity of our diet. Nature Food. 2020 Jan;1(1):33-7.