Defining the Recommended Dietary Allowances (RDAs)
Addressing the Adequate Intake (AI)
Explaining the Dietary Reference Intake (DRI)
Spelling out the terms used to describe amounts of vitamins and minerals in your diet
A healthful diet provides sufficient amounts of all the nutrients that your body needs. The question is, how much is enough?
Today, three sets of recommendations provide the answers, and each comes with its own virtues and deficiencies. The first, and most familiar, is the RDA (short for Recommended Dietary Allowance). The second, originally known as the Estimated Safe and Adequate Daily Dietary Intakes (ESADDI), now shortened to Adequate Intake or simply AI, describes recommended amounts of nutrients for which no RDAs exist. The third is the DRI (Dietary Reference Intake), an umbrella term that includes RDAs plus several innovative categories of nutrient recommendations.
Confused? Not to worry. This chapter spells it all out.
RDAs: Guidelines for Good Nutrition
The Recommended Dietary Allowances (RDAs) were created in 1941 by the Food and Nutrition Board, a subsidiary of the National Research Council, which is part of the National Academy of Sciences in Washington, D.C.
RDAs originally were designed to make planning several days’ meals in advance easy for you. The D in RDA stands for dietary, not daily, because the RDAs are an average. You may get more of a nutrient one day and less the next, but the idea is to hit an average over several days.
For example, the current RDA for vitamin C is 75 milligrams for a woman and 90 milligrams for a man (age 18 and older). One 8-ounce glass of fresh orange juice has 120 milligrams of vitamin C, so a woman can have an 8-ounce glass of orange juice on Monday and Tuesday, skip Wednesday, and still meet the RDA for the three days. A man may have to toss in something else — maybe a stalk of broccoli — to be able to do the same thing. No big deal.
The amounts recommended by the RDAs provide a margin of safety for healthy people, but they’re not therapeutic. In other words, RDA servings won’t cure a nutrient deficiency, but they can prevent one from occurring.
Vitamins and minerals: The essentials
RDAs offer recommendations for protein and 18 essential vitamins and minerals, shown in the following table.
Vitamin A
Folate
Vitamin D
Biotin
Vitamin B12
Vitamin E
Phosphorus
Vitamin K
Magnesium
Vitamin C
Iron
Thiamin (vitamin B1)
Zinc
Riboflavin (vitamin B2)
Copper
Niacin
Iodine
Vitamin B6
Selenium
The newest essential nutrient, choline, won its wings in 2002, but no RDAs have yet been established. Calcium also has an Adequate Intake (AI) rather than an RDA.
Recommendations for carbohydrates, fats, dietary fiber, and alcohol
What nutrients are missing from the RDA list of essentials? Carbohydrates, fiber, fat, and alcohol. The reason is simple: If your diet provides enough protein, vitamins, and minerals, it’s almost certain to provide enough carbohydrates and probably more than enough fat. Although no specific RDAs exist for carbohydrates and fat, guidelines definitely exist for them and for dietary fiber and alcohol.
In 1980, the U.S. Public Health Service and the U.S. Department of Agriculture joined forces to produce the first edition of Dietary Guidelines for Americans (see Chapter 16). A new edition of the Dietary Guidelines has been issued every five years since then to set parameters for what you can consider reasonable amounts of calories, carbohydrates, dietary fiber, fats, protein, and alcohol. According to these guidelines, several general rules advise you to
Balance your calorie intake with energy output in the form of regular exercise. Check out Chapter 5 for specifics on how many calories a person of your weight, height, and level of activity (couch potato? marathon runner?) needs to consume each day.
Make foods with complex carbohydrates and dietary fiber (defined inChapter 8) the (broad?) base of your total daily calories. These should make up to 900 to 1,300 calories and up to 25 grams dietary fiber on a 2,000 calorie per day diet.
Concentrate on unsaturated fats. For more specific guidelines, check out Chapters 16 and 17 for the straight skinny from The Dietary Guidelines 2015 and Chapter 7 for everything you need to know about the individual dietary fats.
Drink alcohol only in moderation. That means one drink a day for a woman and two for a man.
Different people, different needs
Because different bodies require different amounts of nutrients, RDAs currently address as many as 22 specific categories of human beings: boys and girls, men and women, from infancy through middle age. The RDAs recently were expanded to include recommendations for groups of people age 50 to 70 and 71 and older. Eventually, recommendations will be made for people older than 85.
These expanded groupings are a really good idea. In 1990, the U.S. Census counted 31.1 million Americans older than 65. By 2050, the U.S. government expects more than 60 million mostly active older citizens.
If age is important, so is gender. For example, because women of childbearing age lose iron when they menstruate, their RDA for iron is higher than the RDA for men. On the other hand, because men who are sexually active lose zinc through their ejaculations, the zinc RDA for men is higher than the zinc RDA for women.
And gender affects body composition, which influences other RDAs, such as protein: The RDA for protein is set in terms of grams of protein per kilogram (2.2 pounds) of body weight. Because the average man weighs more than the average woman, his RDA for protein is higher than hers. The RDA for an adult male, age 19 or older, is 56 grams; for a woman, it’s 46 grams.
AIs: The Nutritional Numbers Formerly Known as ESADDIs
In addition to the RDAs, the Food and Nutrition Board has created an Adequate Intake (AI) for eight nutrients considered necessary for good health, even though nobody really knows exactly how much your body needs. Not to worry: Sooner or later, some smart nutrition researcher will come up with a hard number and move the nutrient to the RDA list.
You can find the AIs for biotin, choline, pantothenic acid, and vitamin D in Chapter 10, along with the requirements for other vitamins. The AIs for the minerals calcium, chromium, molybdenum, and manganese are in Chapter 11 with the other dietary minerals.
DRI: The Totally Complete Nutrition Guide
In 1993, the Food and Nutrition Board’s Dietary Reference Intakes committee set up several panels of experts to review the RDAs and other recommendations for major nutrients (vitamins, minerals, and other food components) in light of new research and nutrition information. The first order of business was to establish a new standard for nutrient recommendations called the Dietary Reference Intake (DRI). DRI is an umbrella term that embraces several categories of nutritional measurements for vitamins, minerals, and other nutrients. It includes
Estimated Average Requirement (EAR): The amount that meets the nutritional needs of half the people in any one group (such as teenage girls or people older than 70). Nutritionists use the EAR to figure out whether an entire population’s normal diet provides adequate amounts of nutrients.
Recommended Dietary Allowance (RDA): The RDA, now based on information provided by the EAR, is still a daily average that meets the needs of 97 percent of a specific population, such as women age 18 to 50 or men age 70 and older.
Adequate Intake (AI): The AI is a new measurement, providing recommendations for nutrients for which no RDA is set. (Note: AI replaces ESADDI.)
Tolerable Upper Intake Level (UL): The UL is the highest amount of a nutrient you can consume each day without risking an adverse effect.
The DRI panel’s first report, listing new recommendations for calcium, phosphorus, magnesium, and fluoride, appeared in 1997. Its most notable change was upping the recommended amount of calcium from 800 milligrams to 1,000 milligrams for adults age 31 to 50 as well as postmenopausal women taking estrogen supplements; for postmenopausal women not taking estrogen, the recommendation is 1,500 milligrams.
The DRI panel’s second report appeared in 1998. The report included new recommendations for thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin, and choline. The most important revision was increasing the folate recommendation to 400 micrograms a day based on evidence showing that folate reduces a woman’s risk of giving birth to a baby with spinal cord defects and lowers the risk of heart disease for men and women. (See the sidebar “Reviewing terms used to describe nutrient recommendations” in this chapter to brush up on your metric abbreviations.)
As a result of the 1998 DRI panel’s report, the FDA ordered food manufacturers to add folate to flour, rice, and other grain products. (Multivitamin products already contain 400 micrograms of folate.) In May 1999, data released by the Framingham Heart Study, which has followed heart health among residents of a Boston suburb for nearly half a century, showed a dramatic increase in blood levels of folate. Before the fortification of foods, 22 percent of the study participants had folate deficiencies; after the fortification, the number fell to 2 percent.
A DRI report with revised recommendations for vitamin C, vitamin E, the mineral selenium, beta carotene, and other antioxidant vitamins was published in 2000. In 2001, new DRIs were released for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. In 2004, the Institute of Medicine (IOM) released new recommendations for sodium, potassium, chloride, and water, plus a special report on recommendations for two groups of older adults (age 50 to 70 and 71 and over). By 2005, the Food and Nutrition Board had established an AI of 600 IU (international units) vitamin D for men and women older than 71. Put all these findings together, and they spell out the recommendations you find in this chapter.
Table 3-1 shows the most recent RDAs for vitamins for healthy adults; Table 3-2 shows RDAs for minerals for healthy adults. Where no RDA is given, an AI is indicated by an asterisk (*) by the column heading.
† The “official” RDA for vitamin A is still 1,000 RE/5,000 IU for a male, 800 RE/4,000 IU for a female who isn’t pregnant or nursing; the lower numbers listed on this chart are the currently recommended levels for adults.
‡ The current recommendations are the amounts required to prevent vitamin D deficiency disease; recent studies suggest that the optimal levels for overall health may actually be higher, in the range of 800–1,000 IU a day.
Hankering for more details? Notice something missing? Right — no recommended allowances for protein, fat, carbohydrates, and, of course, water. You can find those (respectively) in Chapters 6, 7, 8, and 12.
** The lower recommendation is for postmenopausal women taking estrogen supplements; the higher figure is for postmenopausal women not taking estrogen supplements.
Adapted with permission from Recommended Dietary Allowances (Washington D.C.: National Academy Press, 1989), and DRI panel reports, 1997–2004
The slogan “No Sale Ever Is Final,” printed on the sales slips at one of my favorite clothing stores, definitely applies to nutritional numbers. RDAs, AIs, and DRIs should always be regarded as works in progress, subject to revision at the first sign of a new study. In other words, in an ever-changing world, here’s one thing of which you can be absolutely certain: The numbers in this chapter will change. Sorry about that.
These expanded groupings are a really good idea. In 1990, the U.S. Census counted 31.1 million Americans older than 65. By 2050, the U.S. government expects more than 60 million mostly active older citizens.