Not easily classified
Secondary phytochemicals are a heterogeneous group of the most diverse plant-based substances. They are classed as “secondary” because plants do not need them to build cells or metabolise energy, yet they are still essential for the plant’s survival. Secondary phytochemicals offer protection from pests, UV light and other environmental influences. They also provide colour and fragrance and serve as growth regulators. In contrast to primary phytochemicals, such as carbohydrates, proteins and fats, secondary phytochemicals appear in far fewer quantities.
We now know of around 100,000 secondary phytochemicals; a few thousand of these are found in the foods we eat. The most important are carotenoids, polyphenols, phytosterols, sulfides and monoterpenes. Found in all plants, chlorophyll is also a secondary phytochemical and is used as a colour in the food industry.
Secondary phytochemicals are mostly found in the skins, outer layers and leaves of fruits and vegetables. Nuts, pulses, cereals and oil seeds like sunflower seeds and sesame seeds are important sources. Heat destroys many secondary phytochemicals, so cold-pressed vegetable oils have a clear advantage here, for example. Even if we don’t yet fully understand how secondary phytochemicals work, there are strong indications that they do.
They play an important role in preventive health care, counteracting cardio-vascular disease, strokes and high blood pressure. It’s thought they also help prevent obesity, osteoporosis and asthma and they have neurological, inflammation reducing and antibacterial effects. On average, a varied diet provides around 1.5g of secondary phytochemicals each day – so it is worth opting for diversity in the foods we eat.
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