Apart from these phytochemicals, green leafy vegetables are protective against cancer, especially gastrointestinal system carcinomas, due to high pulp content [ 93 ]. In this group, spinach shows protective effects against cancer by reducing oxidative stress in the body thanks to vitamins A, C, and E, carotenes such as beta carotene and lutein, flavones and flavonoids it contains [ 94 , 95 ].
Broccoli is another vegetable that is effective in protecting against cancer. A number of epidemiological studies have associated broccoli to low incidence of cancer. Sulfurous compounds found in broccoli are cancer preventive agents [ 96 ]. In addition to sulfurous compounds, there are carotenes and other antioxidant vitamins in broccoli. But the most effective compounds in preventing cancer are the sulfurous compounds in broccoli.
These sulfurous compounds inhibit cancer formation by reducing free radicals and preventing cell damage [ 97 ]. Tomato, a good source of beta carotene and lycopene, reduces free radical damage in the DNA that causes cancer and prevents the growth and spread of cancer cells just like green leafy vegetables [ 78 ]. Lycopene is especially protective against prostate cancer [ 78 , 98 ].
In an epidemiological study, consuming tomato and tomato products was found to be associated with a lower incidence of prostate cancer [ 99 ]. Results of a study investigating the relationship of tomatoes and tomato products with cancer revealed that the consumption of tomatoes and tomato products decreased cancer risk [ 98 ]. In another study, lycopene in tomatoes was shown to inhibit the growth and spread of cancer cells in lung cancer by reducing oxidative stress and inducing apoptosis [ ].
Another vegetable in this group associated with cancer is pepper because of the capsaicin it contains. Capsaicin is thought to prevent cancer cells from growing, developing, and spreading [ ]. Preparation and cooking methods can greatly affect the nutritional content and acceptability of vegetables. There is no consensus in the literature as to what is the best way of preserving bioactive compounds while preparing and cooking vegetables [ ]. Some vegetables are subjected to peeling in order to remove their shell or skin and make them more digestible.
Minerals and other nutrients are affected by peeling. This can also cause severe loss of certain vitamins. It is known that peeling before boiling increases the loss of ascorbic acid, folic acid, or other vitamins of group B. Chopping vegetables can also change the bioavailability of bioactive compounds such as vitamins, carotenoids, polyphenols, and flavonoids [ ].
Thawing, cutting, and crashing citrus vegetables can also disrupt antioxidant glucosinolates due to the presence of myrosinase enzyme found in these vegetables [ ]. Cooking improves the flavor of vegetables and enables the nutrients in the vegetables to be more easily used by the digestive system.
However, cooking results in some physical and chemical changes in vegetables [ ]. The effect of cooking procedure may vary depending on the various factors such as cooking technique, temperature, leakage into the cooking environment, solvent used for extraction, surface area exposed to water and oxygen, and pH [ ]. In addition, each food matrix contains different compounds; therefore the same cooking technique may have different effects depending on the type of vegetable [ ]. Cooking techniques affect polyphenol content and antioxidant activity levels in vegetables.
Heat treatment can lead to a change in the chemical structures of vegetables, leading to the breakdown of cells and the degradation of some phenolic compounds from biological structures, the release of phenolics from the food matrix, and the conversion of insoluble phenolics to more soluble forms [ , ]. In addition, the phenolic compounds are soluble in water. Thus, water-based cooking techniques often lead to loss of phenolics by leaking [ ].
It has been reported that food processing has negative effects due to oxidation dependent losses in carotenoids and positive effects as it provides increased bioavailability [ ]. Among the causes of increased carotenoid concentration in heat treatment may be greater extractability, enzymatic breakdowns, and incalculable moisture losses. Heat treatment also causes inactivation of enzymes and degradation of structures in the food matrix leading to increased bioavailability [ , ].
The losses of minerals during preparation and cooking stages of vegetables are closely related to their solubility. Minerals are generally stable against a large number of conditions encountered during cooking, such as heat, oxidation, acidity or alkalinity. Potassium is an abundant mineral found in vegetables, and because of its high solubility in water, it is easily lost by leakage during cooking.
Calcium and magnesium are usually present in an attached form in plant tissue and are therefore not easily lost by leakage. The loss of vitamin C is due in part to oxidative degradation during preparation and cooking and partly due to the leakage of the vitamin into the water used for cooking.
The amount of vitamins degraded during cooking may be quite small compared to the amount lost due to leakage [ ]. Due to its solubility and reactivity, folate is susceptible to potentially large losses during food processing and storage. The chemical stability of folates in plant-based foods may be adversely affected by heat, oxygen exposure, and light intensity.
Since folate is highly soluble, its losses occur by leakage through the water used for washing, boiling, and cooking [ ]. Onion is the richest source of quercetin, which is a flavonoid, and it is most widely used source in diet. Gennaro et al. It was found that other cooking methods and warming treatments did not have a significant effect on flavonoid amount [ ]. Regarding the effects of cooking on onions, Lombard et al.
Potato contains various phenolic compounds, mainly chlorogenic acid and caffeic acid. There are several studies showing that cooking reduces [ ], does not affect [ ] or increases [ , , , ] phenolic compounds in potato. The reason for the increase in phenolic compounds during cooking is attributed to the increase in the extractability of these compounds from the cellular matrix of potato due to the textural changes in its starch structure during cooking [ ].
Carrot is one of the important root vegetables rich in bioactive compounds such as carotenoids and dietary fiber. When the effect of boiling and steaming of frozen carrot on phenolic compound content was investigated, it was determined that phenolic content of carrot was significantly decreased at the end of the boiling process, whereas there was an increase in the steaming method [ ]. The decrease during boiling may be due to the leakage of phenolic compounds into the boiling water. In a study investigating the effect of different cooking methods boiling, steam cooking, and microwave cooking on phytochemical content and total antioxidant capacity TAC of cabbage and black cabbage, which are part of the Brassicaceae family and are rich sources of vitamins and phytochemical compounds such as carotenoids and polyphenols, it was found that the best method in preserving the nutritious quality of vegetables was steam cooking.
It was also shown that fresh vegetables preserved phytochemical compounds and TAC better than frozen samples [ ]. Chang et al. The difference in cooking conditions time and temperature , the type of vegetables, and the interaction between cooking methods and vegetable type may be the cause of differences observed in carotenoid composition. Alvi et al. Dolinsky et al. Pepper Capsicum annuum L. In a study conducted with six species of pepper, three different cooking methods were used frying, boiling, and microwaving and antioxidant properties of peppers after cooking procedures were evaluated.
Reductions in radical scavenging activity RSA and total phenolic contents TP were observed after all cooking procedures, but the reductions after frying and microwaving were not statistically significant when compared to the initial RSA and TP levels. Significant reductions were also observed in TP after 5 and 30 minutes of boiling [ ].
Based on these results, it can be said that the most suitable heat treatment method for peppers are microwave use and frying. If boiling is to be performed, shorter cooking time, less water usage, and consumption of cooking water can also reduce the amount of antioxidants that can be lost. Artichoke, which is characterized by a complex antioxidant profile, contains many bioactive compounds such as glycosides and phenolic compounds, especially caffeicinic acid.
Iron and calcium are key minerals found in some vegetables, with very important roles in the body. Calcium is of vital importance for healthy bones and teeth, and normal muscle function, while iron is involved in cognitive brain function, immunity, normal red blood cell oxygen transport, and the reduction of tiredness and fatigue.
Eating enough iron is especially important for teenage girls and pre-menopausal women, to prevent the development of iron deficiency anaemia. Did you know that our soya beans are sources of iron? Birds Eye Nutrition. Veg Nutrition. Non-Discrimination Statement. Information Quality. Privacy Policy. New Farmers. Disaster Resource Center. An official website of the United States government. Have a Question? Eat plenty every day. Tips to eat more vegetables and fruits each day Keep fruit where you can see it.
Place several ready-to-eat washed whole fruits in a bowl or store chopped colorful fruits in a glass bowl in the refrigerator to tempt a sweet tooth. Explore the produce aisle and choose something new. Variety and color are key to a healthy diet. On most days, try to get at least one serving from each of the following categories: dark green leafy vegetables; yellow or orange fruits and vegetables; red fruits and vegetables; legumes beans and peas; and citrus fruits.
Skip the potatoes. Choose other vegetables that are packed with different nutrients and more slowly digested carbohydrates.
Make it a meal. Try cooking new recipes that include more vegetables.
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