4.10: Summary

An essential nutrient, by definition, is required in the diet for health and normal development. The body needs energy-providing nutrients (carbohydrate, fat, protein), certain amino acids, fatty acids, and vitamins and minerals. Water is also essential to life; it’s the liquid wherein chemical reactions take place and in which substances are transported throughout the body. We lose water mostly through urine and perspiration. Maintaining hydration is important for optimal performance in athletic events.

Carbohydrate, fat, and protein, besides providing energy, are broken down into basic molecular building blocks used to make key substances in the body. The 9 amino acids and 2 fatty acids essential in the diet come from protein and fat, respectively.

The 13 vitamins are classified by whether they’re soluble in fat or water. The 4 fat-soluble vitamins are stored in larger amounts, need to be consumed less often, and are more likely to be toxic when in excess than are the 9 water-soluble vitamins. There are 15 minerals required in the diet. To a certain extent, the body regulates its mineral content by controlling a mineral’s absorption and/or excretion.

Exact nutrient requirements vary within a population, much as height and weight vary. But it’s tedious, expensive, and hard to measure the exact amount of each nutrient needed by an individual. Instead, estimates are based on many studies. Normal diets of healthy populations also give a good indication of the amounts needed.

The main standard in the U.S. for assessing nutritional adequacy of a diet is the RDAs (Recommended Dietary Allowances)—the recommended amounts of nutrients in the daily diet. The amounts are generous, set to cover the needs of virtually all healthy people in the U.S.

RDAs are not minimum requirements. And they don’t need to be met every day (the body stores all nutrients to some extent). RDAs provide for maintaining reserves. Practically speaking, we should average the RDAs over several days. There are several sets of RDAs for different segments of the population, based mainly on age and gender.

RDAs are revised periodically to reflect new information. The current revisions have values called Dietary Reference Intakes (DRIs), which not only include the RDAs but other reference values, such as Tolerable Upper Intake Levels (ULs) to address the issue of toxicity.

Daily Values (DVs) were put together for use in providing nutrient information on labels of food and dietary supplements. There are 4 sets of DVs: (1) Adults and children above age 4 (this set used for most labels), (2) Infants through age 12 months, (3) Children age 1-3 years, (4) Pregnant and lactating women. The DVs are even more generous than RDAs. They come from taking, for each nutrient, the highest RDA for those in each set.

DVs are set at 100%, and each nutrient is given as %DV. In addition, dietary components for which there are no RDAs (e.g., added sugar, fiber) have DVs to emphasize their importance to health. For these, the %DV is based on the recommended amount in a 2000-calorie diet. Regulations also spell out which health claims can be made on food labels, and give precise definitions for such terms as low fat.

ChooseMyPlate.gov (eating certain amounts of foods from the vegetable, fruit, grain, dairy, and meat/meat-substitute groups) and the Dietary Guidelines for Americans help us select a healthy diet. Such a diet needn’t exclude any foods thought of as bad or junk. It’s our overall diet—not individual foods themselves—that tends to be good or bad. Aim for a diet that’s both healthy and pleasurable, beginning early in life and continuing throughout the lifespan.