Dietary Reference Intakes

The Dietary Reference Intakes (DRI) provide estimates of the amounts of nutrients required to prevent deficiencies and maintain optimal health and growth. They consist of the Estimated Average Requirement (EAR), the average daily nutrient intake level estimated to meet the requirement of 50% of the healthy individuals in a particular life stage (age) and gender group; the Recommended Dietary Allowance (RDA), the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97%–98%) individuals in a life stage and gender group; the Adequate Intake (AI), which is set instead of an RDA if sufficient scientific evidence is not available to calculate the RDA; and the Tolerable Upper Intake Level (UL), the highest average daily nutrient intake level that is likely to pose no risk of adverse health effects to almost all individuals in the general population. The energy generated by the metabolism of the macronutrients (9 kcal/g of fat and 4 kcal/g of protein or carbohydrate) is used for three energy-requiring processes that occur in the body: resting metabolic rate, physical activity, and the thermic effect of food. Acceptable Macronutrient Distribution Ranges (AMDR) are defined as the ranges of intake for a particular macronutrient that are associated with reduced risk of chronic disease while providing adequate amounts of essential nutrients.
Adults should consume 45%–65% of their total calories from carbohydrates, 20%–35% from fat, and 10%–35% from protein (Fig.1). Elevated levels of cholesterol in low-density lipoproteins (LDL-C) result in increased risk for coronary heart disease (CHD). In contrast, elevated levels of cholesterol in high-density lipoproteins (HDL-C) have been associated with a decreased risk for CHD. Dietary or drug treatment of hypercholesterolemia is effective in decreasing LDL-C, increasing HDLC, and reducing the risk for CHD. Consumption of saturated fats is strongly associated with high levels of total plasma and LDL-C. When substituted for saturated fatty acids in the diet, monounsaturated fats lower both total plasma cholesterol and LDL-C but maintain or increase HDL-C. Consumption of fats containing ω-6 polyunsaturated fatty acids lowers plasma LDL-C, but HDL-C, which protects against CHD, is also lowered.
Dietary ω-3 polyunsaturated fats suppress cardiac arrhythmias and reduce plasma triacylglycerols, decrease the tendency for thrombosis, and substantially reduce the risk of cardiovascular mortality. Carbohydrates provide energy and fiber to the diet. When they are consumed as part of a diet in which caloric intake is equal to energy expenditure, they do not promote obesity. Dietary protein provides essential amino acids. Protein quality is a measure of its ability to provide the essential amino acids required for tissue maintenance. Proteins from animal sources, in general, have a higher-quality protein than that derived from plants. However, proteins from different plant sources may be combined in such a way that the result is equivalent in nutritional value to animal protein. Positive nitrogen (N) balance occurs when N intake exceeds N excretion. It is observed in situations in which tissue growth occurs, for example, in childhood, pregnancy, or during recovery from an emaciating illness.
Negative N balance occurs when N losses are greater than N intake. It is associated with inadequate dietary protein; lack of an essential amino acid; or during physiologic stresses such as trauma, burns, illness, or surgery. Kwashiorkor occurs when protein deprivation is relatively greater than the reduction in total calories. It is characterized by edema. Marasmus occurs when calorie deprivation is relatively greater than the reduction in protein. No edema is seen. Both are extreme forms of protein-energy malnutrition (PEM). Nutrition Facts labels give consumers information about the nutritional content of packaged foods. Medical assessment of nutritional status includes dietary history, anthropometric measures, and laboratory data. Each life stage has specific nutrition needs. Growth charts are used to monitor the growth pattern of an individual from birth through adolescence. Drug–nutrient interactions are of concern, especially in older adults.

Figure 1: Key concept map for the macronutrients. [Note: *Trans fatty acids are chemically classified as unsaturated.] PEM = protein-energy malnutrition; LDL = low-density lipoprotein; C = cholesterol.