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Antioxidants are substances that prevent damage to cells from highly reactive, unstable molecules called “free radicals.” A balance between antioxidants and free radicals in our body is important for health. If not kept in check, free radicals lead to cell damage linked to a variety of chronic diseases. An antioxidant is a compound that prevents another molecule from becoming oxidised. When molecules in the body become oxidised, free radicals can be formed. Free radicals are very unstable and cause damage within the body as they break down.Antioxidants stabilise free radicals and prevent this damage by donating electrons. Antioxidants are found in broccoli, brussels sprouts, cabbage, cauliflower, tomatoes, corn, carrots, mangos, sweet potatoes, soybeans, cantaloupe, oranges, spinach, nuts, lettuce, celery, liver, fish oil, seeds, grains, kale, beets, red peppers, potatoes, blueberries, strawberries, and black and green tea. As a rule, dark-colored fruits and vegetables have more antioxidants than other fruits and vegetables.

Advantages of Antioxidant in the human system

Protective Action on Inflammatory Bowel Disease: Inflammatory bowel disease (IBD), which includes two complex diseases, ulcerative colitis (UC) and Crohn’s disease, is a chronic inflammatory disorder caused by deregulated immune responses in a genetically predisposed individual. Antioxidant phytochemicals were highly associated with IBD, because quite a lot of them were found to have anti-inflammatory properties. In addition, it was shown that patients with UC often had antioxidant nutrient deficiencies at the time of diagnosis. 

Anti-Diabetes Activity; Diabetes is a major worldwide health problem and characterized by chronic hyperglycaemia which leads to a number of microvascular and macrovascular complications (e.g., endothelial dysfunction and atherosclerosis). There are two types of diabetes, type-1 diabetes (T1D) and T2D. Diabetes is usually accompanied by increased production of free radicals or oxidative stress due to hyperglycemia and hyperlipidemia . It was also demonstrated that, in the course of diabetes and its complications, plasma antioxidants including α- and γ-tocopherol, α- and β-carotene, lycopene, β-cryptoxanthin, lutein, zeaxanthin, retinol and ascorbic acid showed a significant decrease. Cohort studies showed that metabolic homeostasis was improved, and the development of T2D and its complications was delayed or prevented by frequent consumption of wholegrain foods.

Phytochemicals are naturally occurring compounds in plant foods such as fruits, vegetables, whole grains, beans, nuts and seeds. In laboratory studies, many phytochemicals act as antioxidants, neutralizing free radicals and removing their power to create damage.Many phytochemicals also seem to support our body’s ability to balance antioxidants and free radicals. The human antioxidant defense system includes a complex network of enzymes and other compounds working with one another and with antioxidant nutrients supplied by food.Thousands of phytochemicals have now been identified. Many of these have antioxidant activity. Pollution, radiation, cigarette smoke, and herbicides also can create free radicals in your body. Free radicals can damage a cell’s genetic parts and may trigger the cell to grow out of control. These changes may contribute to the development of cancer and other diseases. There are many different groups of phytochemicals which all have different chemical structures. These different types are metabolised differently in the body and may induce different health effects. Examples of phytonutrients include:

Flavonoids (For example, anthocyanins and quercetin): found in soybeans, onions, apples, tea and coffee. The flavonoids in soybeans, chickpeas, and licorice may act a little bit like estrogen, a hormone that might affect the risk of breast cancer that depends on estrogen for its growth.The estrogen-like compounds in these plants are called phytoestrogens. But most phytoestrogens have very weak estrogen-like activity. When a weak estrogen-like substance replaces your body’s natural estrogen’s position, then the weak substance can act as a relative anti-estrogen. By acting in this way, phytoestrogens might help work against breast cancer that depends on estrogen for its growth. But phytoestrogens are present in only small amounts in these foods.

  • Polyphenols (For example, resveratrol and ellagic acid): found in green tea, red wine, grapes, berries and wholegrains
  • Carotenoids (For example, lycopene, lutein, zeaxanthin, beta-carotene): found in red, dark green and orange fruits such as tomatoes, carrots, sweet potatoes, watermelon, leafy greens.
  • Anthocyanins, which give grapes, blueberries, cranberries, and raspberries their dark color, have been shown in the laboratory to have anti-inflammatory and anti-tumor properties.
  • Sulfides, found in garlic and onions, may strengthen the immune system.

Much of the evidence so far on the effects of phytochemicals comes from observing people who eat mainly plant-based diets. These people appear to have markedly lower rates of certain types of cancers and heart disease. Some of the associations between specific phytochemicals and cancer risk reduction are very persuasive, but more research is needed.Some scientists think that you could reduce your cancer risk by as much as 40% by eating more vegetables, fruits, and other plant foods that have certain phytochemicals in them. Research has shown that some phytochemicals may:

  • help stop the formation of potential cancer-causing substances (carcinogens)
  • help stop carcinogens from attacking cells
  • help cells stop and wipe out any cancer-like changes

Some of the most beneficial phytochemicals are:

  • beta carotene and other carotenoids in fruits and vegetables
  • resveratrol in red wine
  • polyphenols in tea
  • isothiocyanates in cruciferous vegetables (members of the cabbage family that include bok choy, collards, broccoli, brussels sprouts, kohlrabi, kale, mustard greens, turnip greens, and cauliflower

Phytochemicals including resveratrol, anthocyanins, and curcumin, can reduce inflammation via inhibition of prostaglandin production and nuclear factor-κB activity, enzyme inhibition, as well as increase of cytokine production. Usually, antioxidant phytochemicals possess strong antioxidant and free radical scavenging abilities as well as anti-inflammatory action, which are also the basis of other bioactivities and health benefits.

Polyphenols could also protect the cardiovascular system, not only from oxidative stress but other damage because they possess other physiological effects, such as blood pressure reduction and inflammation decreasing action. In addition, polyphenols may enhance the total oxidant-scavenging capacities of human blood by binding to red blood cells. Furthermore, the antioxidant activity of apples may mainly come from phenolics and flavonoids because the vitamin C in apples with skin accounts for only 0.4% of the total antioxidant activity. The additive and synergistic effects of phytochemicals in fruit and vegetables could be responsible for their potent antioxidant activities. 

Fruits and plant extracts with high contents of antioxidant phytochemicals show anti-obesity activities both in vitro and in vivo. For example, citrus fruits showed potential inhibitory activity on α-glucosidase and pancreatic lipase in vitro, due to their high contents of antioxidant phytochemicals such as flavanones. Because these phytochemicals are in the fruits, vegetables, beans, and grains you eat, it’s fairly easy to include them in your diet. A carrot, for example, has more than 100 phytochemicals. Nutrition researchers estimate that more than 4,000 phytochemicals have been identified, but only about 150 have been studied in depth. More research is needed to find out which phytochemicals may offer benefits in reducing the risk of cancer. Keep in mind that there is no evidence that taking phytochemical supplements is as good for you as eating the whole fruits, vegetables, beans, and grains that contain them. Most experts strongly believe that it’s the combination of these compounds and the other foods you eat that keeps your body healthy. Loading up on one or two phytochemicals in pill form probably won’t be as beneficial as eating a balanced diet with a variety of foods that includes 5 or more cups of fruits and vegetables per day and food from other plant sources, such as whole-grain breads, cereals, nuts, seeds, rice and pasta, and bean.

Adverse Effects of Antioxidant and Phytochemicals

Although many studies have found protective roles for antioxidant and phytochemicals in chronic diseases, other studies found some discrepancies. For example, fruit juices from red grape, strawberry, cherry or sour cherry showed very strong free radical scavenging activity in the 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity assay and the β-carotene bleaching assay, but they did not show cytotoxic effects on HT29 cells using the same concentrations. That is, there was no correlation between the antioxidant activity and anti-proliferative effects in HT29 cells of these fruit juices. In another study, effects of several antioxidant phytochemicals on the tumor promoting activity of 3,3′,4,4′-tetrachlorobiphenyl were examined in vivo. Coenzyme 10 increased cell proliferation in normal hepatocytes, whereas the other antioxidants (e.g., ellagic acid, β-carotene, curcumin, N-acetyl cysteine, resveratrol, lycopene, and a tea extract) had no effect in either normal or PGST-positive hepatocytes. The results showed that none of the antioxidant phytochemicals produced a clear decrease in the tumor promoting activity of 3,3′,4,4′-tetrachlorobiphenyl in rats. In addition, it was found by a systematic evaluation that the concentrations of vitamin C, vitamin E, α-carotene and β-carotene in dietary were inversely associated with gastric cancer risk, while no such association was observed for blood levels of these antioxidants.

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