Supposedly all of our vitamins and minerals have something called a fractional absorption rate because we only absorb so much from the food we eat. This is not just for supplements. And I am not talking about not eating too much of the nutrients at one time, as is famously expressed about calcium increments and absorption, I am talking about percentages of absorption based on our biological ability. I was wondering how the Daily Values of our nutrients are determined, what is the reasoning and process behind the amounts and do these amounts take into account the fractional absorption? Thank you for any advice or for anyone who tried to help.
asked byMatt_21 (313)
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on December 04, 2011
at 05:03 PM
The RDA, or Recommendation Daily Allowance, of Vitamin C, as well as for other vitamins and minerals, was originally developed during World War II using only sample populations, and were used merely as a point of reference regarding the nutrient levels needed in order to avoid chronic deficiencies in otherwise healthy adults.
In recent years, doctors and nutritionists have observed and reported that because of evolutionary factors, supplementation in much higher doses than the RDA is now necessary for optimum nutrition. For example, in the case of Vitamin C, the RDA is 60 mg/day; please recall from above that this is the daily required intake of Vitamin C at which a healthy adult will not develop scurvy. Presently, many modern health care practitioners now recommend a minimum dosage of 2,000 mg/day in order to support optimum health. Proper levels of Vitamin C (ascorbic acid) in the body not only help to support the immune system, as a properly acidic environment works to inhibit bacterial growth, but also help, for example, to naturally lower blood pressure, counteract food allergies, and rid the body of any accumulations of heavy metals.
The Recommended Dietary Allowance (RDA) was developed during World War II by Lydia J. Roberts, Hazel Stiebeling and Helen S. Mitchell, all part of a committee established by the United States National Academy of Sciences in order to investigate issues of nutrition that might "affect national defense" (Nestle, 35).1 The committee was renamed the Food and Nutrition Board in 1941, after which they began to deliberate on a set of recommendations of a standard daily allowance for each type of nutrient. The standards would be used for nutrition recommendations for the armed forces, for civilians, and for overseas population who might need food relief. Roberts, Stiebeling, and Mitchell surveyed all available data, created a tentative set of allowances for "energy and eight nutrients", and submitted them to experts for review (Nestle, 35). The final set of guidelines, called RDAs for Recommended Dietary Allowances, were accepted in 1941. The allowances were meant to provide superior nutrition for civilians and military personnel, so they included a "margin of safety." Because of food rationing during the war, the food guides created by government agencies to direct citizens' nutritional intake also took food availability into account.
If you google fractional absorption you can find the rates for some of them in various papers, but no actual determination methods.