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PART 4 Regulation and Maintenance
continuing on to adults. RDAs were also set for pregnant and lactat-ing women. The RDAs have been reevaluated every 4–5 years andupdated when necessary on the basis of new information.The RDAs establish a minimum intake of vitamins and mineralsthat should protect almost everyone (97%) in a given group fromdiseases caused by vitamin or mineral deficiencies. Although per-sonal requirements can vary, the RDAs are a good benchmark. Thefurther below the RDAs an individual’s dietary intake is, the morelikely that person is to develop a nutritional deficiency. On theother hand, consuming too much of some vitamins and mineralscan be harmful. For example, the long-term ingestion of3–10 times the RDA for vitamin A can cause bone and muscle pain,skin disorders, hair loss, and an enlarged liver. Consuming 5–10times the RDA of vitamin D over the long term can result in cal-cium deposits in the kidneys, heart, and blood vessels, and consum-ing more than 2 g of vitamin C daily can cause stomachinflammation and diarrhea.
seeds housing most of the minerals and vitamins, are discarded.Minerals and vitamins are often added to refined breads and cere-als to compensate for their loss during the refinement process.A balanced diet can provide all the vitamins and mineralsrequired for good health for most people. Some nutritionists, how-ever, recommend taking a once-a-day multiple vitamin and min-eral supplement as insurance because many people’s diets are notbalanced.
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ASSESS YOUR PROGRESS
22. What are minerals? What is the daily requirement formajor minerals?
23. List several minerals the body needs and a function ofeach.
Daily Values for Nutrients
Daily Values are dietary values that appear on food labels to helpconsumers plan a healthful diet. Daily Values are based on twoother sets of reference values: Reference Daily Intakes and DailyReference Values.
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Predict 2
What would happen if vitamins were broken down during digestionrather than being absorbed intact into the circulation?
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ASSESS YOUR PROGRESS
17. What are vitamins, essential vitamins, and provitamins?
18. Name the fat-soluble vitamins and the water-solublevitamins.
19. List some of the functions of vitamins in the body.
20. What are Recommended Dietary Allowances (RDAs)? Whyare they useful?
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21. What are some symptoms of specific vitamin deficiencies?
Reference Daily Intakes (RDIs) are based on the 1968 RDAsfor certain vitamins and minerals. RDIs have been set for fourcategories of people: infants, toddlers, people over 4 years ofage, and pregnant or lactating women. Generally, the RDIs areset to the highest 1968 RDA value of an age category. Forexample, the highest RDA for iron in males over 4 years of ageis 10 mg/day and, for females over 4 years of age, 18 mg/day.Thus, the RDI for iron is set at 18 mg/day. Daily Reference Values (DRVs) are set for total fat, saturatedfat, cholesterol, total carbohydrate, dietary fiber, sodium, potas-sium, and protein.
Minerals
Minerals (min′er- ă lz) are inorganic nutrients that are necessaryfor normal metabolic functions. The minerals are divided into twogroups, major minerals and trace minerals, based on the amountrequired in the diet for good health. The daily requirement for major minerals is 100 mg or more daily. The daily requirementfor trace minerals is less than 100 mg daily. The trace mineralsare needed in such low amounts that the required amount for someis unknown. Minerals constitute about 4–5% of total body weight.Some minerals are components of other important molecules inthe body, such as coenzymes, a few vitamins, and hemoglobin.Minerals are involved in a number of important functions, includ-ing establishing resting membrane potentials and generatingaction potentials, adding mechanical strength to bones and teeth,combining with organic molecules, and acting as coenzymes, buf-fers, and regulators of osmotic pressure. Table 25.3 lists importantminerals and their functions.People ingest minerals alone or in combination with organicmolecules, as well as obtain them from both animal and plantsources. However, mineral absorption from plants can be limitedbecause the minerals tend to bind to plant fibers. Refined breadsand cereals contain hardly any minerals or vitamins because theseeds used to make them are crushed, and the outer parts of the
Having two standards on food labels, RDIs for vitamins andminerals and DRVs for other nutrients, was thought to be moreconfusing for consumers than having one standard. Therefore, theRDIs and DRVs were combined to form the Daily Values.The Daily Values appearing on food labels are based on a2000 kcal reference diet, which approximates the weight mainte-nance requirements of postmenopausal women, women who exer-cise moderately, teenage girls, and sedentary men (figure 25.2).On large food labels, additional information is listed based on adaily intake of 2500 kcal, which is adequate for young men. How-ever, government standards do not require that all possible DailyValues be listed on food labels.The Daily Values for energy-producing nutrients are deter-mined as a percentage of daily kilocalorie intake: 60% for carbo-hydrates, 30% for total fats, 10% for saturated fats, and 10% forproteins. The Daily Value for fiber is 14 g for each 1000 kcal ofintake. The Daily Values for a nutrient in a 2000 kcal/day diet canbe calculated on the basis of the recommended daily percentage ofthe nutrient and the kilocalories in a gram of the nutrient. Forexample, carbohydrates should compose 60% of a 2000 kcal/daydiet, or 1200 kcal/day (0.60 × 2000). Since there are 4 kcal in agram of carbohydrate, the Daily Value for carbohydrateis 300 g/day (1200/4).