Once it's established that a nutrient is essential for good health, the Food and Nutrition Board and the Institute of Medicine create a recommended dietary allowance according to age and gender. The RDA requirements are considered adequate for 98 percent of all healthy people. Because the requirements are designed to cover the vast majority of the population, you may be able to undershoot the percentages and still obtain all the nutrients you need.
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An RDA is set for protein as well as vitamins A, C, D, E, K, B-6 and B-12. It is also established for the B vitamins thiamin, riboflavin, niacin and folate and the minerals calcium, copper, phosphorus, magnesium, molybdemum, iron, zinc, iodine and selenium. The RDAs not only vary according to gender and age but also for pregnant or lactating women.
How to Use the RDA
The RDA is purposefully set high to cover a large percentage of the population and usually exceeds the needs of 97.5 percent of the age and gender categories it encompasses. Dietitian Joanna Larsen explains that 67 percent of a given nutrient usually covers the average person, so this is the minimum amount you could consume of the RDA of each nutrient and likely stay healthy. Exceeding the RDA minimum requirements is unlikely to cause harm, as long as you stay below any upper limits established.
Limitations of the RDA
The RDA figures are established for healthy people. Those who are malnourished, suffering from health problems or taking specific medications may not find the RDA applicable. For even healthy people, the recommendations only provide a guideline because they can't account for individual variations in nutritional needs.
Only an Average
The RDA is an average daily intake. Trying to hit the exact percentage of each nutrient as recommended every day is nearly impossible. If you consume a varied diet that contains foods from all the major food groups -- fruits, vegetables, grains, proteins, dairy and oils -- you should meet the RDA requirements.
All Those Acronyms
Don't confuse the RDA with the estimated average requirements, which are the amounts of a nutrient that seem sufficient for half the population. Also know there is an "adequate intake" set for nutrients for which no estimated average requirement, and thus no RDA, has been established. The average intake is established using scientific judgment rather than proof, based on the average amount of a nutrient that a group of healthy people consumes.