Chemical food additives can be derived from either synthetic or natural sources, and are usually used for one of four purposes. They serve as food preservatives to prolong shelf life and prevent spoilage in conditions of heat and humidity, they are used as coloring agents and flavor enhancers, or they are added to increase the nutritional value of foods. Processed foods tend to have a lot of chemical food additives that are introduced into products in minute amounts, but the most common food additive in bulk are those designed as flavor enhancers. These include natural sugar, high fructose corn syrup, and artificial sweeteners like aspartame. Other common flavor enhancers include monosodium glutamate (MSG) and natural spices with either synthetic or natural origins such as the flavors spearmint, almond, and vanilla.
While sweeteners are the most common category of food additive, two others added specifically for health benefits are also very widespread. These include the mineral iodine, which is usually added as potassium iodide to serve as both a preservative and to prevent thyroid diseases caused by lack of the compound in the diet, and vitamin D, which is added to milk to prevent bone diseases as well as promote eye and skin health. Both iodine and vitamin D have been added to foods in the US since the 1920s and 1930s.
Another key area where natural additives are used to fortify a food's nutritional value is with the addition of the B vitamins, iron, and folic acid to processed white flour. Most of these vitamins are naturally present in flour but are lost during the milling process. They have been added back into the end product since the 1940s to prevent diseases like pellagra and beriberi in children and adults, and spina bifida in newborns.
While artificial additives can fall within a range of about 20 different categories. from anticaking agents to emulsifiers and humectants, several of the most common are used to prevent the natural fats and oils in foods from spoiling. These chemical food additives include butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), as well as fat substitutes that taste like fat such as olestra and sterol esters. Other chemical food additives that are used as both fat substitutes and food stabilizers or preservatives are gums acquired from various plants such as seaweed. These include carrageenan, guar gum, locust bean gum, and other well-known additives like xanthan and arabic gums.
Of the hundreds of different chemical food additives, two categories of preservatives that are commonly used are known to cause health problems in excess. These include sodium nitrate compounds, which can serve the multiple role of being preservatives, coloring agents, and flavoring agents at the same time, and are widely used in cured meats as well as elsewhere to prevent bacterial growth. Sulfites are another broad category of chemical food additives used to prevent discoloration in dried fruit and to keep seafood like shrimp and lobster fresh. These compounds are especially troublesome to people with asthma and some types of allergies, as, in high enough concentrations, they can cause anaphylactic shock which can lead to death if not immediately treated.