How Are the RDAs Determined

The RDAs are determined based upon in-depth research studies, including those performed to determine "balance." Balance studies are designed to determine how much of a specific nutrient humans need to eat in order to balance that which is normally lost daily from the body and to maintain appropriate levels of that nutrient in the body. When these studies were performed, scientists observed that there was quite a bit of variability among the balances of different individuals. A hypothetical representation of a particular nutrient's balance is depicted in Figure 3.1.

Based on balance studies, researchers are able to determine estimated average requirements for specific gender and age groups for a given nutrient. Here they add up all of the individual balance levels and divide by the total number of people they assessed. The result is the Estimated Average Requirement or EAR. In this figure we see that the RDA for this nutrient is set well above the EAR. In fact the RDA is set two standard deviations (a measure of statistical variation) above the average. By doing so the RDA would be adequate to meet the needs of 97 to 98 percent of the people in the study. Knowing this, the RDAs will provide more of the nutrient than needed for balance for most individuals. From this we can certainly understand that the RDAs are not really personal recommendations but are more appropriate for making recommendations for populations. For example, the RDA for vitamin C for adult women of all ages is

10 20 30 40 50 60 70 80 90 100 110 Balance quantity (mg) theoretical essential nutrient

1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 Balance quantity (calories) energy

Figure 3.1 A hypothetical representation of a particular nutrient's balance.

75 milligrams, which should avoid deficiency and promote general health for about 97 to 98 percent of adult women.

It should be noted that the recommendation for energy was not set to include 97 to 98 percent of the population, but only 50 percent (see Figure 3.1). If the recommendation was set to include 98 percent of the population this might lead to weight gain for many people using the recommendation for energy as a guideline.

Beyond balance studies, other research studies involving the relationship between the essential nutrients and the body are reviewed to help determine the RDA. For example, the RDA for many nutrients during the years of rapid growth and during pregnancy must account for balance as well as an additional amount of a nutrient to allow for these periods of rapid growth. Furthermore, RDA determinations do not take into consideration acute disease, medications, or exercise training. Only recently have RDA considerations included chronic diseases such as osteoporosis and heart disease. However, at this time the RDAs and AIs are still considered to be below a level that would optimally support the prevention of several major diseases such as heart disease and cancer.

How Are Nutrition Recommendations Used on Food Labels?

By law food manufacturers must follow specific guidelines on their food labels with the purpose of informing consumers of the nutritional content of the food and to protect against misleading statements on food labels. Food labels contain the Nutrition Facts (Figure 3.2), which in most cases provide at least the following information:

  • a listing of ingredients in descending order by weight
  • serving size
  • servings per container
  • amount of the following per serving: total calories, total protein, calories contributed by fat, total fat, saturated fat, cholesterol, total carbohydrate, sugar, dietary fiber, vitamin A, vitamin C, calcium, iron, sodium

As many individuals try to plan their nutrient intake, the nutrition facts also include the Daily Value (DV). The DV uses reference nutrition standards to indicate how a single serving of a food item relates to nutrition recommendation standards and include:

  • a maximum of 30 percent total calories from fat, or less than 65 grams total
  • a maximum of 10 percent total calories from saturated fat, or less than 20 grams
  • a minimum of 60 percent total calories from carbohydrate
  • 10 percent of total calories from protein

Nutrition Facts

Serving Size 1 cup (228g)

Servings Per Container 2

Amount Per Serving

Calories 250 Calories from Fat 110

% Daily Value*

Total Fat 12g

18%

Saturated Fat 3g

15%

Trans Fat 1.5g

Cholesterol 30mg

10%

Sodium 470mg

20%

Total Carbohydrate 31 g

10%

Dietary Fiber Og

0%

Sugars 5g

Protein 5g

Vitamin A

4%

Vitamin C

2%

Calcium

20%

Iron

4%

•Percent Daily Values are based on a 2,000 calorie diet.

Your Daily Values may be higher or lower depending on

your calorie needs:

Calories:

2,000

2,500

Total Fat Less than

65g

80g

Sat Fat Less than

20g

25g

Cholesterol Less than

300mg

300mg

Sodium Less than

2,400mg

2,400mg

Total Carbohydrate

300g

375g

Dietary Fiber

25g

30g

Figure 3.2 Example of a nutrition facts panel on a food label.

  • 10 grams of fiber per 1,000 calories
  • a maximum of 300 milligrams of cholesterol
  • a maximum of 2,400 milligrams of sodium

Daily Values on food labels are designed to help people make better informed nutrition choices.

Furthermore, the DV for other nutrients, such as vitamins A and C, thia-min, riboflavin, niacin, calcium, and iron, are founded upon RDA-based standards and are presented in Table 3.3. However, these standards are not as specific for gender and age as the RDAs and therefore one quantity will apply to all people.

Daily Values are expressed as a percentage and is based on a 2,000 and/or a 2,500 calorie intake, which approximates most American's recommended energy intake. Therefore a food providing 250 calories per serving will be listed as either 13 percent or 10 percent DV for a 2,000 and 2,500 calorie intake, respectively. Beyond the nutrition facts, food manufacturers must also follow federal guidelines for other statements they choose to make on a food label. Some of the statements are listed in Table 3.4.

The Nature of Food 59 Table 3.3 Daily Values (DV) Used for Nutrition Labeling

Nutrient

Amount

Nutrient

Amount

Biotin

Calcium

Chloride

Chromium

Copper

Folic acid

Iodine

Iron

Magnesium Manganese Molybdenum Niacin

Pantothenic acid

Phosphorus

Riboflavin

Selenium

Thiamin

1,000 mg

300 re 1,000 mg 3,400 mg

75 re

20 mg 10 mg

Vitamin A Vitamin B-12 Vitamin B-6 Vitamin C Vitamin D Vitamin E Vitamin K Zinc Total fat Saturated fat Cholesterol Total carbohydrate Fiber Sodium Potassium Protein

5,000 IU

300 mg

400 IU

6 re

2 mg 60 mg

30 IU

80 re 15 mg

300 g 25 g mg = Milligrams, |ig = micrograms, IU = international units.

Source: Center for Food Safety and Applied Nutrition, 2002; National Academy of Sciences

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Responses

  • valentin
    How are rdas determined?
    2 months ago
  • james
    Who determined the rda and how do they know it works?
    13 days ago

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