In the food industry, it appears as powder or crystals that are transparent and tasteless. It can help with the flow of dry, powered things by preventing clumping owing to moisture, because it can absorb around 120% of its weight in moisture.
Thus, it is used in flours, powdered soups, coffee whitener powder, vanilla powder, baking powder, powdered sugars, spices, etc. In commercial beer production, it’s used as a defoaming agent. It is also used in vitamins. For a complete list, see here: http://www.codexalimentarius.net/gsfaonline/additives/details.html?id=284 [Ed: link valid as of September 2010.]
One or two people suspect that Silicon Dioxide may cause things such as Fibromyalgia Syndrome and Chronic Fatigue Syndrome.
It is listed for acceptable daily intake by the Joint FAO/WHO Expert Committee on Food Additives in 1969. American law allows up to 2% usage in a product, though usage is more in the range of just 1 to 2%.
Your body just passes almost all of it on, as it really doesn’t play any role in us that we know of. Though, the possible role of silicon deficiency with some diseases is being researched.
Fraser, Ivan. Do Additives in Health Food Supplement and Pharmaceutical Tablets Make us Ill? The Truth Campaign Magazine, Issue 33.
Igoe, Robert S. Dictionary of Food Ingredients. Van Nostrand and Reinhold Company. 1983.
Joint FAO/WHO Expert Committee on Food Additives. Geneva 25 June – 4 July 1973. Toxicological evaluation of some food additives including anticaking agents,antimicrobials, antioxidants, emulsifiers and thickening agents.WHO FOOD ADDITIVES SERIES NO. 5. Published Geneva 1974. Rep. Ser., 1974, No. 539; FAO Nutrition Meetings Report Series, 1974, No. 53.
Winter, Ruth A Consumer’s Dictionary of Food Additives. Crown Publishers, Inc., New York. 1978.