Understanding terms used to describe nutrient recommendations

Nutrient listings use the metric system. RDAs for protein are listed in grams. The RDA and AIs for vitamins and minerals are shown in milligrams (mg) and micrograms (mcg). A milligram is 1⁄1000 of a gram; a microgram is 1⁄1000 of a milligram. Vitamin A, vitamin D, and vitamin E are special cases.

For instance, one form of vitamin A is preformed vitamin A, a form of the nutrient that your body can use right away. Preformed vitamin A, known as retinol, is found in food from animals —liver, milk, and eggs. Carotenoids (red or yellow pigments in plants) also provide vitamin A. But to get vitamin A from carotenoids, your body has to convert the pigments to chemicals similar to retinol. Because retinol is a ready-made nutrient, the RDA for vitamin A is listed in units called retinol equivalents (RE). One mcg (microgram)

RE is approximately equal to 3.33 international units (IU, the former unit of measurement for vitamin A).
Vitamin D consists of three compounds: vitamin D1, vitamin D2, and vitamin D3. Cholecalciferol, the chemical name for vitamin D3, is the most active of the three, so the RDA for vitamin D is measured in equivalents of cholecalciferol. Your body gets vitamin E from two classes of chemicals in food: tocopherols and tocotrienols. The compound with the greatest vitamin E activity is a tocopherol: alpha-tocopherol. The RDA for vitamin E is measured in milligrams of alphatocopherol equivalents (a-TE).

Understanding DRI: Dietary Reference Intake

In 1993, the Food and Nutrition Board’s Dietary Reference Intakes committee established 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 the:

• 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 for individuals, the amount of any one nutrient known to protect against deficiency.
• 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 mg to 1,000 mg for adults ages 31 to 50 as well as post-menopausal women taking estrogen supplements; for post menopausal women not taking estrogen, the recommendation is 1,500 mg.

The second DRI Panel 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 mcg 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.

As a result of the 1989 DRI Panel report, the FDA ordered food manufacturers to add folate to flour, rice, and other grain products. (Multivitamin products already contain 400 mcg 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. And 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 (ages 50 to 70 and 71 and over). Put these findings all together, and they spell out the recommendations.

The complete reports on which this table is based are available online. Go to www.iom.edu/Object.File/Master/21/372/0.pdf. Prefer hard copy? IOM plans to consolidate the reports into one book to be published late in 2006.
Hankering for more details? Notice something missing? Right — no recommended allowances for protein, fat, carbohydrates and, of course, water.

AIs: The Nutritional Numbers Formerly Known as ESADDIs

In addition to the RDAs, the Food and Nutrition Board created Estimated Safe and Adequate Daily Dietary Intakes (ESADDI), now renamed 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. Or not. In the meantime, new reports have established AIs for various age groups for the following nutrients:

• Pantothenic acid
• Molybdenum
• Biotin
• Manganese
• Choline
• Fluoride
• Calcium
• Chromium

Different people has 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 ages 50 to 70 and 70 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 who are older than 65. By 2050, the U.S. Government expects more than 60 million to be alive and kickin’.

You wouldn’t want these baby boomers to miss their RDAs, now would you? But who you are affects the recommendations. 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. Finally, gender affects body composition, which influences RDAs.

Consider 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.

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. This report has been modified many times. The latest set of recommendations, issued in the spring of 2005, sets parameters for what you can consider reasonable amounts of calories, carbohydrates, dietary fiber, fats, protein, and alcohol. According to these guidelines, as a general rule, you need to

• Balance your calorie intake with energy output in the form of regular exercise.
• Eat enough carbohydrates (primarily the complex ones from fruits, vegetables, and whole grains) to account for 45 to 65 percent of your total daily calories. That’s 900 to 1,300 calories on a 2,000-calorie diet.
• Take in an appropriate amount of dietary fiber, currently described as 14 grams dietary fiber for every 1,000 calories.
• Get no more than 20 to 35 percent of your daily calories from dietary fat. Therefore, if your daily diet includes about 2,000 calories, only 400 to 700 calories should come from fat. Less than 10 percent of your daily calories should come from saturated fatty acids, and your daily diet should have less than 300 mg cholesterol. Eat as little trans fat as possible. The Nutrition Facts label on foods now shows a gram amount for trans fats, but there’s no upper limit because any amount is considered, well, less than okey-dokey.
• If you choose to drink alcoholic beverages, do so in moderation, meaning one drink a day for a woman and two for a man.

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 mg for a woman and 90 mg for a man (age 18 and older).

One 8-ounce glass of fresh orange juice has 120 mg 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.