Dietary Intake Acronyms
Prepare yourself for acronyms galore. The Dietary Reference Intakes (DRIs) include the Recommended Daily Allowances (RDA) [also called the Recommended Daily Intake (RDI)] adequate intakes (AI), the tolerable upper intake levels (UL) and the Acceptable Macronutrient Distribution Range (AMDR). These values are established by the Institute of Medicine (IOM) of the National Academy of Sciences (NAS).
Recommended Dietary Allowance - RDA
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RDA stands for Recommended Dietary Allowance. RDA is defined as the average daily dietary nutrient intake level sufficient to meet the nutrient requirement of nearly all (~ 98 percent) healthy individuals. Values are determined based on gender and age. For example, a 65 year old male will need a different amount of iron per day than a 20 year old female. These values are based on extensive research. The chart to the right shows the most recent values established by the Institute of Medicine for vitamins.
Representation for Establishing EAR for Calcium
Estimated Average Requirement is abbreviated EAR. The following explanation will hopefully help you understand how scientists decide the recommended intake of specific nutrients.
In order to better explain this concept, I'm going to use this figure to the right using the example of calcium. The average requirement for most adults is 1000 mg per day. To determine the RDA for calcium, let's say we are going to evaluate 130 women, aged 51-70 years of age. We test each woman to determine her individual need for calcium and then plot that value on a chart. If you look at the graph you can see a number of squares. Each square on the chart above represents a value for one of the women in the study. Woman A is 1 of 7 women who need about 850 mg/day. Woman B is 1 of 12 women who need 1025 mg/day. Woman C is 1 of 2 women who need about 1180 mg/day. Some women require more calcium and some women require less.
If we were to take all 130 values and average them, we would get an average of 1000 mg/day. This is called the Estimated Average Requirement. The EAR is the average amount of calcium a woman between the age of 51-70 needs per day.
When considering a recommended intake for calcium in this age group, the RDA is not placed at 1000 mg/day, the average (EAR). It is place at 1200 mg, because we want to make sure almost all of the women aged 51-70 are getting enough calcium on a daily basis. This value covers 98% of the women in this age group. If the recommendation was 1000 mg/day (placed at the EAR) almost half of those tested would not be getting enough calcium. For example, woman C needs 1180 of calcium a day. If her goal was to obtain 1000 mg/day, she would not be taking in enough calcium on a daily basis. Therefore, the RDA is placed at 98% of the estimated intake value to make sure 98% of people are getting their required nutrients.
Now you might say “If I’m person A and I only need 850 mg of calcium per day, why do I need to get 1000 mg?” You don’t, but there are not enough resources to test every single person, for every single nutrient, during every stage of their life, to find out their individual requirements. In addition, with the way the current intakes are determined, there isn't a clinical need to test everyone. The 98% recommendation is a safe recommendation, even for those individuals who require less. It is set well below the upper limit (UL). You might notice that there is one women in our small study that may not be meeting her needs. It looks like she requires slightly over the 1200 mg recommendation. Why not set the recommendation at 110%, 150% or even 250% of the EAR (eg: 1300 mg of calcium or 1500 mg or 2500 mg of calcium) to be sure to cover everyone? The upper intake limit (UL) is 2000 mg for this age group. Even a recommendation of 1500 mg might be too high for woman A.
DRI studies use large populations and repetition to get solid information for the RDAs (130 people is considered very small considering there are about 318 million people in the US). In some instances, there is not enough evidence to make a recommendation for a nutrient intake value. In this instance, an Adequate Intake level (AI) is established.
In order to better explain this concept, I'm going to use this figure to the right using the example of calcium. The average requirement for most adults is 1000 mg per day. To determine the RDA for calcium, let's say we are going to evaluate 130 women, aged 51-70 years of age. We test each woman to determine her individual need for calcium and then plot that value on a chart. If you look at the graph you can see a number of squares. Each square on the chart above represents a value for one of the women in the study. Woman A is 1 of 7 women who need about 850 mg/day. Woman B is 1 of 12 women who need 1025 mg/day. Woman C is 1 of 2 women who need about 1180 mg/day. Some women require more calcium and some women require less.
If we were to take all 130 values and average them, we would get an average of 1000 mg/day. This is called the Estimated Average Requirement. The EAR is the average amount of calcium a woman between the age of 51-70 needs per day.
When considering a recommended intake for calcium in this age group, the RDA is not placed at 1000 mg/day, the average (EAR). It is place at 1200 mg, because we want to make sure almost all of the women aged 51-70 are getting enough calcium on a daily basis. This value covers 98% of the women in this age group. If the recommendation was 1000 mg/day (placed at the EAR) almost half of those tested would not be getting enough calcium. For example, woman C needs 1180 of calcium a day. If her goal was to obtain 1000 mg/day, she would not be taking in enough calcium on a daily basis. Therefore, the RDA is placed at 98% of the estimated intake value to make sure 98% of people are getting their required nutrients.
Now you might say “If I’m person A and I only need 850 mg of calcium per day, why do I need to get 1000 mg?” You don’t, but there are not enough resources to test every single person, for every single nutrient, during every stage of their life, to find out their individual requirements. In addition, with the way the current intakes are determined, there isn't a clinical need to test everyone. The 98% recommendation is a safe recommendation, even for those individuals who require less. It is set well below the upper limit (UL). You might notice that there is one women in our small study that may not be meeting her needs. It looks like she requires slightly over the 1200 mg recommendation. Why not set the recommendation at 110%, 150% or even 250% of the EAR (eg: 1300 mg of calcium or 1500 mg or 2500 mg of calcium) to be sure to cover everyone? The upper intake limit (UL) is 2000 mg for this age group. Even a recommendation of 1500 mg might be too high for woman A.
DRI studies use large populations and repetition to get solid information for the RDAs (130 people is considered very small considering there are about 318 million people in the US). In some instances, there is not enough evidence to make a recommendation for a nutrient intake value. In this instance, an Adequate Intake level (AI) is established.
References
- Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes, Vitamins. Food and Nutrition Board, Institute of Medicine, National Academies. United States Department of Agricultural. Last accessed April 7, 2016. https://fnic.nal.usda.gov/sites/fnic.nal.usda.gov/files/uploads/recommended_intakes_individuals.pdf
- Estimated average intake image created by Christine Dobrowolski, derived from Sizer F., Whitney E. Nutrition, Concepts and Controversies. 13th ed. Cengage Learning.
Last updated April 7th, 2016