Most important representatives of the secondary plant substances

Secondary plant substances

A group of herbal ingredients has made a name for itself in recent years: the so-called secondary plant substances (SPS).
Since they are only found in very small quantities in plants and, unlike carbohydrates , proteins and fats, have no nutritional value of their own, they were hardly given any attention for a long time. They serve plants as coloring agents, to protect against diseases and pests and to regulate their growth.

However, it is now assumed that they have important protective functions not only for plants but also for humans. That is why they are also called bioactive substances. Scientists have found that people who frequently consume fruit and vegetables and thus also phytochemicals are far less likely to be affected by cardiovascular diseases and cancer .

The exact role that secondary plant substances play in this has not yet been clearly established. Scientists agree, however, that the secondary plant substances should not be consumed individually and in high doses as a food supplement. On the contrary: some of these substances – overdosed and taken uncontrollably – can even increase the risk of cardiovascular diseases and cancer. They work best in combination with other substances – just as they occur in natural foods. A balanced and healthy diet thus ensures the best supply of these important substances.

The group of secondary plant substances contains chemically very different compounds, only a small part of which has been researched. At the moment it is assumed that there will be a total of 50,000 to 100,000.

The most important representatives of the  secondary plant substances are:

  • Anthocyanins
  • Carotenoids
  • Flavonoids
  • Glucosinolates
  • Monoterpenes
  • Phytoestrogens
  • Phytosterols
  • Polyphenols
  • Protease inhibitors
  • Saponins
  • Sulfides


Anthocyanins belong to the natural group of flavonoids. They are responsible for the red, purple and blue colors of many flowers, fruits and vegetables. Anthocyanins are said to have antioxidant, vascular protective, and anti-inflammatory properties. They are also said to slow down platelet aggregation and influence visual processes.

Anthocyanins in red, purple, and blue berries and fruits

Red, purple and blue colored berries and fruits such as blackberries, raspberries, blueberries, grapes and cherries as well as juices or red wines made from them are rich in these secondary plant substances.

Healthy nutrition instead of dietary supplements

Taking food supplements with anthocyanins does not make sense because the anthocyanins supplied in this way are almost not absorbed via the digestive tract. As a result, no concentration in the blood is reached that would have an effect. It is better to eat healthily.

Carotenoids (provitamin A) and β-carotene

Carotenoids are widespread in the plant kingdom. They give fruits and vegetables a yellow-red color. Some of them are converted into vitamin A in the body , which is why they are also known as provitamin A.

The best-known provitamin A: ß-carotene

The best-known provitamin A is β-carotene, which is abundantly contained in carrots and has a wide range of effects: It has an antioxidant effect , strengthens the immune system and supports cell communication. However, increased vitamin A intake during pregnancy – either through dietary supplements or frequent liver meals – can damage the child.

The strongest antioxidant effect of the carotenoids has lycopene, which is mainly found in tomatoes. It can be particularly well absorbed from cooked tomatoes or tomato sauces.

At first it looked like high doses of β-carotenes increased the risk of prostate cancerReduce. However, recent studies indicate that the opposite is the case – especially among smokers . The same applies to lung cancer in smokers. No preventive effect has been shown for other types of cancer or heart disease . However, this only applies to increased intake – for example through dietary supplements – and not to carotenoids, which are absorbed through a balanced and healthy diet and thus in combination with other nutrients.

The carotenoids lutein and zeaxanthin may protect the retina of the eye and prevent the development of macular degeneration and cataracts .

Two to four milligrams a day

The recommended intake for adults is two to four milligrams of β-carotene per day. A combined intake of β-carotene and vitamin E through appropriate foods is recommended . Taking high, uncontrolled β-carotene doses – as is usually the case with food supplements – is not recommended. This is especially true for smokers. It is better to ensure a balanced, healthy mixed diet.


Flavonoids are secondary plant substances that are responsible for the coloration of fruits and flowers. Flavonoids play an important role in the prevention of chronic diseases such as cardiovascular diseases , rheumatic diseases and tumor prevention.

Anti-inflammatory, antioxidant and antibiotic

Flavonoids are said to have a vasodilator, anti-inflammatory, antioxidant and antibiotic effect. They also inhibit the formation and growth of blood vessels, which is an important factor in preventing tumors.

Flavonoids are found in grapes, apples, pears, onions, aubergines, soy, and black and green tea, for example. The German Nutrition Society (DGE) estimates that we consume around 50 to 200 milligrams of flavonoids a day.


Glucosinolates are also called mustard oil glycosides. They contain sulfur and nitrogen, which gives many plants a pungent or bitter taste.

Antimicrobial properties

In naturopathy, glucosinolates are often used because of their antimicrobial properties, as they work against bacteria, viruses and fungal infections. For example, they are found in horseradish, mustard, cress, and cabbage vegetables such as Brussels sprouts and broccoli.


Monoterpenes serve as flavorings and are the main component of essential oils. They are mainly found in various types of fruit such as oranges, apricots and grapes as well as in herbs and spices.

Monoterpenes are said to prevent cancer

This group of phytochemicals includes, for example, carvone, which is contained in caraway, and menthol from peppermint. Monoterpenes are said to prevent cancer and inhibit the growth of microorganisms.

Phytoestrogens – the plant estrogens

Phytoestrogens – also called Phytoserms – are herbal ingredients that have an estrogen-like effect. Their estrogen effect is weaker than that of natural human and synthetic estrogens (0.1 percent of the estradiol effect).
Phytoestrogens are only reminiscent of estrogen in their structure. Due to their similarity, they trigger both activating and inhibiting effects on the body’s estrogen receptors. They also have an antioxidant effect.

Isoflavones, lignans and coumestans

The best known phytoestrogens are isoflavones , lignans and coumestans . Isoflavones are mainly found in legumes such as soybeans and red clover. The most important representatives of the isoflavones are genistein and daidzin. Lignans are found primarily in flax seeds, whole grains, berries and flax seeds.

After isoflavones have had positive effects on cardiovascular diseases , menopausal symptoms and especially on the prevention of breast cancer in recent yearsrecent studies have shown that closer inspection is necessary. The effects describe in animal experiments or they cannot be differentiated from other possible causes. Lately it has even been suggested that isoflavones accelerate the growth of hormone-dependent breast cancer. The positive effects on mild menopausal symptoms such as hot flashes, sleep disorders and depressive moods are probably comparable to those of the placebo effect. The protective effect of isoflavones against the development of osteoporosis seems possible at the moment, but the data situation does not yet allow a clear statement.

No recommendation for food supplements

A soy-rich diet is currently expect to have positive effects on the cardiovascular system and a reduced risk of osteoporosis and breast cancer. There is no recommendation for an additional intake of isoflavones via dietary supplements. When taking nutritional supplements, you should be aware of potentially undesirable side effects such as risk of breast cancer, an inhibitory effect on the thyroid gland, and changes in the lining of the uterus.

Phytosterols – plant-based cholesterol-lowering drugs

Phytosterols are similar in structure to cholesterol and are mainly found in fatty foods such as oils, nuts and plant seeds. Abundant sources are sunflower seeds, sesame seeds, soybeans and cold-pressed soybean oil. Over 40 different phytosterols are known to date – the most important representative is β-sitosterol.

Cholesterol lowering effect

Because of their similar structure, phytosterols reduce the absorption of food cholesterol from the intestine and therefore lead to a lowering of the cholesterol level in the blood. It is also believe to lower the risk of colon cancer .

Due to its cholesterol-lowering effect, this group of phytochemicals in particular has led to the development of “functional foods” such as special diet margarine.

Polyphenols – flavonoids and phenolic acids

Polyphenols comprise a group of different substances that plants use as yellow, red, blue or purple coloring agents. They include, for example, phenolic acids.
Flavonoids are mainly found in the outer layers of plants – for example in the skin of grapes and apples. Onions, nuts and grains also contain polyphenols. Well-known representatives of these plant substances are quercetin and rutoside.

Polyphenols have a broad spectrum of activity: They have a strong antioxidant , antimicrobial and anti-inflammatory effect and protect against cancer and thrombosis .

Protease inhibitors

Protease inhibitors are proteins that can inhibit enzymes in the body that break down protein from food into amino acids. However, they should also counteract the development of inflammation and cancer .

The body can produce protease inhibitors by itself

Protease inhibitors are found, for example, in wheat, barley, rice, flaxseed, tomatoes and soybeans. The human body can also produce protease inhibitors itself – for example to control inflammation.


Saponins are compounds that usually taste very bitter. These phytochemicals are widespread in plant foods.

Saponins are mainly found in legumes

Legumes in particular – such as soybeans – have a high saponin content. But spinach, tomatoes, asparagus, oats and liquorice are also good sources of these phytochemicals. For example, many saponins to have a positive effect on cholesterol levels.


Sulphides are sulphurous compounds find in garlic, leeks, onions, shallots and chives, for example. They have an antibacterial effect. Sulphides are also to affect blood clotting and promote digestion.

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