Epidemiologic studies have consistently shown that consumption of fruit and vegetables plays a major role in the prevention of chronic diseases. In fact, the protective effect of fruits and vegetables against cancer appears to be mainly due to the content of phytochemicals in plant foods.


Phytochemicals are secondary plant substances that can be found in fruit, vegetables, grains, and other plant foods. Today, more than 5000 phytochemicals have been identified. It is estimated that there are more than 100,000 different unidentified phytochemicals present in plant foods.

Some phytochemicals are plant pigments (about 2000), that give plants their colour, especially carotenoids and anthocyanins. Carotenoids are responsible for the yellow, orange, and red colour of many fruits and vegetables, whereas anthocyanins can be found in rich red, blue, and purple plant foods. All the coloured phytochemicals have antioxidant properties.


To discriminate phytochemicals which have a proven positive effect on human health from others which don´t, the term phytonutrients is used. Thus, phytonutrients are phytochemicals with a proven positive effect on human health.

“Phytonutrients are phytochemicals with a proven
positive effect on human health”

As stated above, there are more than 5000 phytochemicals known today. In the only 150 to 200 plants humans use as plant foods worldwide, there could be thousands of different phytonutrients, which are still unknown.

An important website for phytochemicals lists 51 different phytonutrients with proven health benefits in clinical studies. Phytonutrients can be classified into different groups, according to their chemical structure.

The most important groups are:

  • Allyl sulfides
  • Anthocyanins
  • Carotenoids
  • Lectins
  • Phytoestrogens, Isoflavones
  • Phytosterols
  • Polyphenols, Flavonoids and Lignans

The most studied phytonutrients are carotenoids and polyphenols.

Very well phytonutrients are:

  • Allyl sulfides in garlic and onions
  • Flavanoids in fruits
  • Indole-3-carbinol
  • Isoflavones in soy beans
  • Lycopene in tomatoes
  • Resveratrol in red wine, blueberries, cranberries, and dark chocolate

Health benefits of phytonutrients

Clinical studies have shown health benefits from phytochemicals for various types of diseases and health issues. Phytochemicals can:

  • Lower LDL-cholesterol levels
  • Prevent cardiovascular (heart) disease
  • Prevent diabetes mellitus
  • Have a neuroprotective effect
  • Improve the vision
  • Reduce inflammation
  • Stabilize the blood pressure
  • Stimulate the immune system

Properties of phytonutrients in plant foods

Phytochemicals have different effects in the human body. The most well known effects are the antioxidative effect and the anti-bacterial effect.

  • Antioxidant – protect our cells against oxidative damage
  • Anti-bacterial effect – anti-bacterial properties.
  • Stimulation of enzymes – stimulate important enzymes
  • Interference with DNA replication – might prevent cell division of cancer cells.
  • Hormonal action – Isoflavones resemble human estrogens

Phytonutrients can prevent oxidative stress

It is well known that phytonutrients are able to neutralise free radicals. By preventing oxidative stress, phytonutrients are able to prevent cancer and cardiovascular disease, as well as other chronic diseases.

Oxidative stress

Cells in our body are constantly exposed to a variety of oxidising agents. Oxidising agents are present in the air we breathe, the food we eat, the drinks we drink, or they are be produced by metabolic activities within our cells. To remain healthy and for optimal physiologic conditions, our body needs to establish a balance between oxidants and antioxidants.

“Oxidative stress dramatically increase the
risk for cancer and heart disease”

Overproduction of oxidants can cause an imbalance, which leads to oxidative stress. Oxidative stress can also be the result from chronic bacterial, viral, or parasitic infections. Oxidative stress can lead to the production of free radicals that damage biomolecules like proteins, DNA, and lipids, resulting in an increased risk for cancer and cardiovascular disease.


Oxidative stress is involved in the development of a wide range of various chronic diseases. Numerous studies have shown that phytochemicals with antioxidant activity can greatly reduce the risk of cancer and cardiovascular disease, like heart attack and stroke.

“Phytochemicals with antioxidant can greatly reduce the
risk for cancer and heart disease”

Antioxidants have the property to neutralise free radicals. Molecules with antioxidative properties in our diet are vitamins, phytonutrients and other molecules, like glutathione. Well known examples of vitamins with antioxidant properties are vitamin A, C, and E.

“Most of the antioxidant activity in apples comes from phytochemicals – 99.6%”

Vitamin C is a strong antioxidant. Apples are rich in Vitamin C. However, Vitamin C in apples contributes only to less than <0.4% of total antioxidant activity. Most of the antioxidant activity in apples (99.6%) comes from phytochemicals, not from vitamin C!

If you want to read more about vitamins, read more here