Secondary plant substances - what are these substances?

Fruits and vegetables are waiting with a special "secret weapon" against cancer and a variety of other diseases. The phytochemicals that make fruits and vegetables for their own protection can also protect us humans from disease.

What do secondary metabolites do?

Numerous scientific studies prove that phytochemicals

  • increase the body's defenses
  • protect against infections with fungi, bacteria or viruses
  • lower cholesterol
  • have a favorable influence on blood sugar levels and blood pressure
  • Can prevent vessel blockage

Through these effects, fruits and vegetables prevent cancer and cardiovascular disease. Therefore, the "5 am Tag campaign" promotes a much higher consumption of fruits and vegetables, as the Germans reach so far.

Protection for plants and humans

So far, researchers have discovered about 30, 000 different phytochemicals, including more than 10, 000 in edible plants. In each type of fruit and vegetable is found a different composition of these bioactive helper.

The functions of the individual phytochemicals are different. Some regulate the growth of the plant or serve as colors and fragrances. Others protect the plants from pests, bacteria or fungi. Phytochemicals also enhance protection against disease in the human body.

The "1 x1" of the phytochemicals

Phytochemicals are divided into different groups according to their structure. The most important among them are carotenoids, flavonoids (as a subgroup of polyphenols), glucosinolates and sulfides.


Only 600 different bioactive substances belong to the group of carotenoids. The best known of these is beta-carotene, which is thought to have a cancer-preventing effect.

Carotenoids are the dyes in red and yellow-colored vegetables and fruits: carrots, red peppers, pumpkins, apricots and tomatoes are top of the list. However, they are also particularly rich in green vegetables, for example in kale, savoy cabbage, spinach and lamb's lettuce. Here the green chlorophyll has covered the orange-red color.


Like the carotenoids, the flavonoids are able to neutralize "free radicals", aggressive oxygen compounds in the body, and thus prevent the development of cancer. In addition, there is evidence from studies that protect against heart attack, kill germs and strengthen the immune system.

Flavonoids are eaten with almost all types of fruit and vegetables. Typical of flavonoid-rich plants are the rich red colors, as they are known from beetroot, red cabbage, eggplant, cherries and grapes.


Sulfides give garlic, onions, leeks and chives their typical pungent taste. They promote digestion and can protect against stomach and colon cancer. In addition, they prevent cholesterol deposits in the arteries.


Glucosinolates are highly concentrated in all types of cabbage, contained in cress, radish and radish. These secondary plant substances are also of great importance for the fight against cancer. They stimulate the body's detoxification, inhibit the growth of microorganisms and reduce the risk of gastric ulcer formation.

Make the most of the valuable

  • Pay attention to fresh and mature goods when shopping. Ripe fruits and vegetables contain the largest amount of bioactive substances, much less in immature fruits.
  • In many fruits and vegetables, the secondary plant substances are particularly numerous in the shell or directly below. Therefore, apples, pears, carrots or cucumbers should be washed and brushed shortly before eating, but not peeled. If fruits and vegetables remain in the water, easily soluble, valuable ingredients are quickly lost.
  • Some secondary plant compounds, such as carotenoids, get heat relatively well, while others, such as glucosinolates, are sensitive to it. Therefore, it is always better to cook fruits and vegetables only briefly and gently and to eat a part as raw food.
  • Finished fruit and vegetable products, such as frozen foods, preserves, dried fruits and juices, are produced with gentle processing methods and are indispensable in everyday cooking. They also supply many phytochemicals. For example, lycopene, a carotenoid, can be better absorbed by tomatoes when processed previously.
  • The biggest enemy of some phytochemicals is light. Especially the carotenoids lose their effect quickly when fruits and vegetables are in the sunlight. Eat fresh produce as fast as you can to get the maximum portion of valuable plant compounds.
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