The World Health Organization recommends that to reduce the incidence of heart disease and the risk of some cancers, each person should eat 5 servings (100 grams each) of vegetables and fruits per day. The Canadian government even suggests 10 servings of vegetables and fruits per day. To understand the mystery of how fruits and vegetables prevent diseases, we must first start with the characteristics of free radicals.
The Domino Effect – Understanding the Characteristics of Free Radicals
Free radicals are extremely chemically reactive. They can steal a hydrogen atom from any molecule to become a stable molecule, or they can add to a double bond in an unsaturated molecule to form a new free radical. The nature of free radicals is like a domino effect; one free radical can trigger a chain of reactions, generating a series of new free radicals. Before encountering a free radical scavenger, the rapid chain reaction initiated by free radicals can continue indefinitely. Therefore, free radicals are highly destructive to human cells.
Because the rate of cancer development is similar to the speed of free radical chemical reactions, this characteristic of free radical chemistry suggests that the occurrence of cancer may be related to the generation of free radicals in the human body. Furthermore, let's look at the characteristics of metabolic reactions in living organisms.
Climbing the "Mountain": Understanding the Characteristics of Human Metabolic Reactions
When synthesizing organic compounds in a laboratory, simply mixing the raw materials together will not produce the reactants. Only by heating the raw materials or subjecting them to high temperatures, high pressure, or strong acids and bases can experimenters obtain the desired synthetic products. This is because between the raw materials and the final product, there is an "energy barrier mountain" that hinders the chemical reaction. Only through external conditions such as heating, which increases the kinetic energy of the raw material molecules enough to allow them to overcome the reaction "energy barrier mountain," can the chemical reaction occur.
However, under the mild conditions of the human body, complex molecules such as cholesterol and sex hormones are produced smoothly. The reason is that the human body contains many highly specific enzymes that catalyze the chemical reactions that need to occur. These enzymes form specific complexes with the reactants, and the formation of these complexes weakens the chemical bonds in the reactant molecules that are about to react, making them extremely prone to homolytic cleavage to form two free radicals. The newly formed free radicals quickly react with molecules of another reactant to produce the products the body needs. This is a typical characteristic of all metabolic reactions that occur in living organisms.
Ergosterol in food can be converted into vitamin D2 by exposure to sunlight, and 7-dehydrocholesterol in the human body can be converted into vitamin D3 by exposure to sunlight. These two forms of vitamin D are products obtained from free radical chemical reactions initiated by ultraviolet light in sunlight. Ultraviolet light can also stimulate the generation of other free radicals and reactive oxygen in the skin.
Clearing Free Radicals: Utilizing the Properties of Antioxidants
Carotenoids The secret to how eating vegetables and fruits prevents disease lies in the two ways free radicals can react with carotenoids in them: 1. Stealing a hydrogen atom from a carotenoid molecule to form a stable compound and a carotenoid free radical. 2. A free radical adding to a double bond in a carotenoid molecule to form a new carotenoid free radical. Carotenoid free radicals are highly stable free radicals that lack the ability to undergo chemical reactions with other molecules, and therefore have no destructive effect on other molecules in the human body. When two carotenoid free radicals meet, they can form a dimeric carotenoid molecule, or undergo a disproportionation reaction to form a normal carotenoid molecule and a carotenoid molecule with a triple bond. This is why carotenoids can clear free radicals.
Polyphenolic compounds Compounds containing multiple benzene rings and more than one hydroxyl group on the benzene rings are called polyphenolic compounds. The vast majority of polyphenolic compounds belong to the broad category of flavonoids. There are more than 4,000 known flavonoids. Anthocyanins are natural pigments of the flavonoid class. Because anthocyanins appear blue, purple, and red in alkaline, neutral, and acidic environments respectively, fruits and vegetables with purplish-black, purplish-red, and some red colors all contain anthocyanins.
When a free radical encounters a polyphenolic molecule, the free radical can steal a hydrogen atom from the hydroxyl group of the polyphenolic molecule, forming a stable molecule and a polyphenolic free radical. Polyphenolic free radicals are also highly stable free radicals that lack the ability to undergo chemical reactions with other molecules, and therefore also have no destructive effect on other molecules in the human body. When two polyphenolic free radicals meet, they combine to form a stable dimeric molecule. For the same reason that carotenoids clear free radicals, this is also why polyphenolic substances can clear free radicals.
It is precisely because carotenoids and polyphenolic substances have large conjugated systems in their molecules and are themselves unstable molecules that when they encounter reactive oxygen in the human body, they will undergo oxidation reactions first. After they consume the reactive oxygen, other substance molecules that make up the cells will not be damaged by oxidative reactions. Therefore, carotenoids and polyphenolic substances are all antioxidants that protect the human body.
Other substances with unsaturated bonds (such as vitamin C, lycopene, etc.) also have certain antioxidant capabilities. For example, after undergoing an oxidation reaction, vitamin C can form oxalic acid, which is then excreted from the body in urine.