Why do tomatoes mainly look red, carrots and apricots orange, peppers and corn yellow, while apples, broccoli and Brussels sprouts usually look green, but blueberries, blackberries and grapes are blue again? And what do the terms phytochemicals, antioxidants and free radicals, lycopene or beta-carotene have to do with the colors of fruits and vegetables?
The colors in fruits and vegetables are caused by phytochemicals. Phyto means that it comes from the plant. Phytochemicals are chemicals that come from the plant itself. There are hundreds of thousands of different phytochemicals and all of those phytochemicals have different positive effects on the health of the people who eat these fruits and vegetables. In order to get as many different nutrients as possible, it is important that you eat fruits and vegetables from different color groups.
Many phytochemicals contain antioxidants. This means that these phytochemicals help us to keep our bodies healthy, for example by fighting free radicals. Free radicals are chemical compounds that contain an unpaired electron. These free radicals can be harmful because they can damage or destroy DNA and cell membranes, which in turn can lead to diseases such as cancer. The best advice for good health is therefore always to eat many different types of fruit and vegetables.
Tomatoes, pink grapefruit and watermelon contain a lot of lycopene. Scientific research has shown that lycopene is an antioxidant that can protect us against prostate cancer. Raspberries and strawberries contain ellagic acid. This is a substance that also has anti-cancer effects. In addition, red pepper and tomatoes are packed with beta-carotene and vitamin C. Beta-carotene is converted by our body into vitamin A. Vitamin A helps to make our immune system stronger. So very healthy.
Yellow products (such as yellow peppers, corn and pumpkin) contain a lot of beta-carotene and other carotenoids. In addition, corn is a good source of lutein, a substance that is very good for the eyes.
Orange vegetables (carrot, sweet potato) and fruit (apricot, mango, orange, mandarin) also contain a lot of beta-carotene. Citrus fruits in particular are rich in vitamin C, which in turn protects against free radicals.
The color green is found in many types of cabbage (broccoli, Brussels sprouts, kale). But also in leafy vegetables (spinach) and fruit (apples and kiwi). The brightest green vegetables contain the most phytochemicals. One of those phytochemicals is the antioxidant chlorophyll (chlorophyll). But in addition to chlorophyll, green vegetables often contain beta-carotene. Green cabbage varieties are a source of glucosinolates. Some laboratory studies have shown that glucosinolates may protect against cancer.
Blue and purple often indicate the presence of anthocyanins. Anthocyanins are another group of substances that eliminate free radicals. Many dark-colored berries also contain vitamin C, while beetroot contains substances that can lower the risk of high blood pressure.
White can be found in garlic, onion and leek, but also in cauliflower, parsnips and mushrooms. The onion family in particular is a source of allicin. This is a substance that falls under ‘natural antibiotics’. Allicin also helps lower blood pressure.
Vitamin D and pancreatic cancer
Dr. Bueno-de-Mesquita from the University Medical Center in Utrecht is investigating (with financial support from the World Cancer Research Fund) whether there is a link between vitamin D and the development of pancreatic cancer. Pancreatic cancer is a very aggressive form of cancer, of which little is known about the risk factors. A number of studies appear to show a link between vitamin D and protection against this form of cancer. The team of Dr. Bueno-de-Mesquita investigates whether there is a connection between:
- taking vitamin D through food;
- the concentrations of vitamin D in the blood.
and the risk of developing pancreatic cancer.
Diet and the development of head and neck cancer
Dr. Schouten from Maastricht University is investigating whether diet influences the risk of head and neck cancer.
With financial support from the World Cancer Research Fund, Dr. Schouten is conducting a so-called ‘prospective cohort study’ into head and neck cancer (such as larynx , mouth and throat cancer). A cohort study is a study in which all subjects participating in the study come from a specific age group. These people are followed over a large number of years. Prospective means that a group of people is taken into consideration at a certain point in time. It is examined how many of those people will suffer from a certain disease during the research period(…). A disease that can then be associated with certain habits or circumstances(…). It is already known that smoking and drinking alcohol are risk factors for developing head and neck cancer. However, more and more evidence is emerging that may lead to the conclusion that diet also plays a role in the development of these cancers. However, convincing evidence for this has not yet been found.
The research looks for the connection between:
- the consumption of vegetables, fruit, meat and fat;
- the intake of vitamins and carotenoids;
- the amount of selenium in the toenail.
and the risk of developing head and/or neck cancer.
Important advice from the World Cancer Research Fund
The World Cancer Research Fund advises everyone to apply the three-color rule. The three-color rule means that people who want to stay healthy should always try to eat at least three different colors of fruit and vegetables with their main meal. The WKOF suggests the following ideas:
- a fruit salad of apple, kiwi and orange;
- a pasta with spinach, yellow pepper and tomatoes;
- a salad of white cabbage, green apple, blue grapes, grated carrot and onion.