# 14 - 343 Nutrient Requirements and Dietary Assessment

### 343 Nutrient Requirements and Dietary Assessment

Flum DR: Acute appendicitis—appendectomy of the “antibiotics first” 

strategy. N Engl J Med 372:1937, 2015.
Khan S et al: Endoscopic retrograde appendicitis therapy: Is it really a 
need of the hour. Ann Surg 277:e1, 2023.
Moris D et al: Diagnosis and management of acute appendicitis adults. 
JAMA 326:2299, 2021.
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systematic review. BMC Med 9:139, 2011.
Talan DA, DiSaverio S: Treatment of acute uncomplicated appendi­
citis. N Engl J Med 385:1116, 2021.
Vons C et al: Amoxicillin plus clavulanic acid versus appendicectomy 
for treatment of acute uncomplicated appendicitis: An open-label, 
non-inferiority, randomised controlled trial. Lancet 377:1573, 2011.
Section 2	 Nutrition
Johanna T. Dwyer

Nutrient Requirements 

and Dietary Assessment
PART 10
Disorders of the Gastrointestinal System
Nutrients are substances that are essential but not synthesized in suf­
ficient amounts in the body and therefore must be supplied by the 
diet. Nutrient requirements for groups of healthy persons have been 
determined experimentally. The absence of essential nutrients leads 
to growth impairment, organ and metabolic dysfunction, and failure 
to maintain nitrogen balance or adequate status of protein and other 
nutrients. For good health, we require energy-providing nutrients (pro­
tein, fat, and carbohydrate), vitamins, minerals, and water. Require­
ments for organic nutrients include 9 essential amino acids, several 
fatty acids, glucose, 4 fat-soluble vitamins, 10 water-soluble vitamins, 
dietary fiber, and choline. The inorganic nutrients include 4 minerals, 
7 trace minerals, 3 electrolytes, and the ultra trace elements that must 
also be supplied by diet. Individuals of different ages and physiologic 
states differ in the amounts of nutrients they require.
Conditionally essential nutrients are not required in the diet but 
must be supplied to certain individuals such as those with genetic 
defects; pathologies such as infection, disease, or trauma with nutri­
tional implications; and some developmentally immature infants 
who need them because they do not synthesize inositol, taurine, 
arginine, and/or glutamine in adequate amounts. Many other organic 
and inorganic bioactive compounds that are present in foods and 
dietary supplements may also have health effects, including pesticides, 
heavy metals like lead, phytochemicals, zoochemicals, and microbial 
products.
■
■ESSENTIAL NUTRIENT REQUIREMENTS
Energy 
The estimated energy requirement (EER) is the predicted 
average requirement to maintain energy balance and health in an adult 
of a defined age, sex, weight, height, level of physical activity, and life 
stage. For weight to remain stable, energy intake must match total 
energy expenditure (TEE). The major components of TEE are resting 
energy expenditure (REE) and the physical activity level (PAL), and 
minor components include the energy cost of metabolizing food (ther­
mic effect of food, or specific dynamic action) and cold-induced (shiv­
ering) thermogenesis. The average energy intake is ~2600 kcal/d for 
American men and ~1800 kcal/d for American women, but individuals 
vary with body size and activity level. Although estimates introduce 
considerable error, energy intakes are usually calculated from formulas 

rather than measuring TEE directly. In individuals whose weights are 
stable, for males, REE = 900 + 10m, and for females, REE = 700 + 7m, 
where m is mass in kilograms. The calculated REE is then multiplied 
by the appropriate PAL to account for physical activity that ranges from 
1.4 (inactive) for individuals who perform only essential activities of 
daily living (e.g., 30 minutes walking and 90 minutes light to moderate 
activity) to 1.6 (low active), 1.75 (active), and 2.05 (very active). The 
result is the estimated energy (EER) or intake. When describing their 
PALs, sedentary, inactive, and low active individuals tend to overes­
timate, and so in practice, use of PALs of 1.2 to 1.4 may be closer to 
their actual activity levels. The EER provides a rough target for plan­
ning caloric needs for a person of a certain age, sex, weight, height, 
and physical activity level who is neither gaining nor losing weight. 
For further discussion of energy balance in health and disease, see 
Chap. 345.
Protein 
Dietary protein consists of both “essential” (e.g., not 
synthesized endogenously and must be supplied by diet) and “nones­
sential” (e.g., synthesized endogenously or obtained from diet) amino 
acids that are all required for protein synthesis. The nine essential 
amino acids are histidine, isoleucine, leucine, lysine, methionine/
cystine, phenylalanine/tyrosine, threonine, tryptophan, and valine. 
Several amino acids, such as alanine, arginine, aspartic acid, glutamic 
acid, glutamine, and glycine can also be converted to glucose and used 
for energy and gluconeogenesis. When energy intake is inadequate, 
protein intake must be increased, because ingested amino acids are 
diverted into pathways of glucose synthesis and oxidation. In extreme 
energy deprivation, protein-calorie malnutrition may ensue (Chap. 345).
For adults, the recommended dietary allowance (RDA) for protein is 
~0.8 g/kg desirable body mass per day, assuming that energy needs are 
met and that the protein is of relatively high biological value. Current 
recommendations for a healthy diet call for at least 10–14% of calories 
from protein. Most American diets provide at least those amounts. Bio­
logic value tends to be highest for animal proteins, followed by proteins 
from legumes (beans), cereals (rice, wheat, corn), and roots. Combina­
tions of plant proteins that complement one another in their essential 
amino acid profiles or combinations of animal and plant proteins can 
increase biologic value and lower total protein intakes necessary to 
meet requirements. In healthy people with adequate diets, the timing 
of protein intake over the course of the day has little effect.
Protein needs increase during growth, pregnancy, lactation, and 
rehabilitation after injury or undernutrition. Tolerance to dietary pro­
tein is decreased in renal insufficiency (with consequent uremia) and 
in liver failure. Usual protein intakes can precipitate encephalopathy in 
patients with cirrhosis of the liver.
Fat and Carbohydrate 
Carbohydrate (4 kcal/g), fat (9 kcal/g), and 
protein (4 kcal/g) all provide energy. So does alcohol (ethanol) (7 kcal/g), 
but it is not a nutrient. Fats are a concentrated source of energy and 
constitute, on average, 34% of calories in U.S. diets. However, for 
optimal health, fat intake should total no more than 30% of calories. 
Saturated fat and trans-fat should be limited to <10% of calories and 
polyunsaturated fats to <10% of calories, with monounsaturated fats 
accounting for the remainder of fat intake. At least 45–55% of total 
calories should be derived from carbohydrates, with <10% and prefer­
ably <6% from added sugars. The brain requires ~100 g of glucose per 
day for fuel; other tissues use ~50 g/d. Some tissues (e.g., brain and 
red blood cells) rely on glucose supplied either exogenously or from 
muscle proteolysis. Over time, during hypocaloric states, adaptations 
that lower carbohydrate needs are possible.
Water 
For adults, 1–1.5 mL of water per kilocalorie of energy 
expenditure is sufficient under usual conditions to allow for normal 
variations in physical activity, sweating, and the diet’s solute load. 
Water losses include 50–100 mL/d in the feces; 500–1000 mL/d 
by evaporation or exhalation; and, depending on the renal solute 
load, ≥1000 mL/d in the urine. If external losses increase, intakes must 
increase accordingly to avoid underhydration. Fever increases water 
losses by ~200 mL/d per °C; diarrheal losses vary but may be as great 
as 5 L/d in severe diarrhea. Heavy sweating, vigorous exercise, and

vomiting also increase water losses. When renal function is normal and 
solute intakes are adequate, the kidneys can adjust to increased water 
intake by excreting up to 18 L of excess water per day (Chap. 393). How­
ever, obligatory urine outputs can compromise hydration status when 
there is inadequate water intake or when losses increase in disease or 
kidney damage.
Infants have high requirements for water because of their large sur­
face area to volume ratios, their inability to communicate their thirst, 
and the limited capacity of the immature kidney to handle high renal 
solute loads. Increased water needs during pregnancy are ~30 mL/d. 
During lactation, milk production increases daily water requirements 
so that ~1000 mL of additional water is needed, or 1 mL for each mil­
liliter of milk produced. Special attention must also be paid to the water 
needs of the elderly, who have reduced total-body water, blunted thirst 
sensation, and frequently use medications such as diuretics.
Other Nutrients 
See Chap. 344 for detailed descriptions of 
vitamins and minerals.
■
■DIETARY REFERENCE INTAKES AND RDAS
Fortunately, human life and well-being can be maintained within a 
fairly wide range of most nutrient intakes. However, the capacity for 
adaptation is not infinite—too much, as well as too little, intake of 
a nutrient can have adverse effects itself or decrease health benefits 
conferred by another nutrient. Therefore, benchmark recommendations 
regarding nutrient intakes have been developed to guide menu develop­
ment and clinical practice. They are referred to in the United States and 
Canada as the dietary reference intakes (DRIs) and are set by National 
Academy of Medicine’s (formerly Institute of Medicine [IOM]) Food 
and Nutrition Board and Health Canada. The recommendations apply 
to the general population, including those with or at risk for chronic 
diseases, overweight, and obesity. Exceptions may be needed for 
individuals with severe comorbidities, diseases, disabilities, or use of 
medications known to alter energy or some nutrient requirements. The 
DRIs supplanted the recommended dietary allowances (RDAs)—the 
single reference values used in the United States until the early 1990s. 
DRIs now include an estimated average requirement (EAR) as well as 
other reference values used for dietary planning: the RDA, the adequate 
intake (AI), the chronic disease risk reduction intake (CDRR), and the 
tolerable upper level (UL). The DRIs also include acceptable macronu­
trient distribution ranges (AMDRs) for protein, fat, and carbohydrate. 
The types of evidence and criteria used to establish nutrient require­
ments vary by nutrient, age, and physiologic group. The current DRIs 
for vitamins and elements are provided in Tables 343-1 and 343-2, 
respectively. Table 343-3 provides DRIs for water and macronutrients. 
Energy has neither an RDA nor a UL because intakes above or below 
requirements lead to weight gain or loss; EERs are used instead and 
are discussed in Chap. 345 on energy balance in health and disease.
Estimated Average Requirement (EAR) 
When florid manifes­
tations of the classic dietary-deficiency diseases such as rickets (defi­
ciency of vitamin D and calcium), scurvy (deficiency of vitamin C), 
xerophthalmia (deficiency of vitamin A), and protein-calorie malnutri­
tion were common, nutrient adequacy was inferred from the absence 
of their clinical deficiency signs. Later, biochemical and other earlier 
changes were used that appeared long before the deficiency was clini­
cally apparent. Today, criteria of adequacy are based on biologic mark­
ers when they are available, and to sensitive biochemical, physiologic, 
or behavioral tests that reflect early changes in regulatory processes; 
maintenance of body stores of nutrients; or, if available, the amount 
of a nutrient that minimizes the risk of chronic degenerative disease. 
However, relevant biomarkers of disease risk are often not available, 
and the long time lags between intake and disease outcomes further 
complicate the picture.
The EAR is the amount of a nutrient estimated to be adequate for 
half of the healthy individuals of a specific age and sex. It is not an 
effective estimate of nutrient adequacy in individuals because it is a 
median requirement for a group, with 50% of individuals in a group 
falling below and 50% falling above the requirement. Thus, a person 
with a usual intake at the EAR has a 50% risk of inadequate intake. For 

these reasons, the other standards described below are more useful for 
clinical purposes.

Recommended Dietary Allowances 
The RDA is the nutrient 
intake goal for planning diets of individuals. It is the average daily 
dietary intake level that meets the nutrient requirements of nearly all 
healthy persons of a specific sex, age, life stage, or physiologic condi­
tion (e.g., pregnancy or lactation). The RDA is set two standard devia­
tions above the EAR to ensure that the needs of virtually any individual 
are met. The risk of dietary inadequacy increases as one’s intake falls 
below the RDA. However, the RDA is an overly generous criterion for 
evaluating nutrient adequacy because, by definition, the RDA exceeds 
the actual requirements of all but ~2–3% of the population. Therefore, 
many people whose intake falls below the RDA are still getting enough 
of the nutrient.
The RDAs are used to formulate food guides such as the U.S. 
Department of Agriculture’s (USDA) MyPlate Plan for individuals 
(https://www.choosemyplate.gov/resources/MyPlatePlan), as well as to 
create food-exchange lists for therapeutic diet planning. An online tool, 
available at https://www.nal.usda.gov/fnic/dri-calculator/, allows health 
professionals to calculate individualized daily nutrient recommenda­
tions for dietary planning based on the DRIs.
The RDAs are also used as a standard for labels describing the nutri­
tional content of foods and nutrient-containing dietary supplements. 
On food labels, the nutrient content in a food is stated by weight and/
or as a percentage of the daily value (DV), a variant of the RDA used on 
the nutrition facts panel that, for an adult, represents the highest RDA 
for an adult consuming 2000 kcal.
CHAPTER 343
Adequate Intake (AI) 
Some nutrients lack an EAR and so an 
RDA cannot be set. In this circumstance, the AI is used, based on 
observed or experimentally determined approximations of nutrient 
intakes in healthy people. In the DRIs, AIs rather than RDAs are pro­
posed for nutrients consumed by infants (up to age 1 year) as well as 
for chromium, fluoride, manganese, sodium, potassium, pantothenic 
acid, biotin, choline, fiber, and water consumed by persons of all ages.
Nutrient Requirements and Dietary Assessment 
Tolerable Upper Levels (UL) 
Healthy individuals derive no 
established benefit from consuming nutrient levels above the RDA or 
AI. In fact, excessive nutrient intake can disturb body functions and 
cause acute, progressive, or permanent disabilities. The tolerable UL 
is the highest level of chronic (usually daily) nutrient intake that is 
unlikely to pose a risk of adverse health effects for most of the popula­
tion. Data on the adverse effects of large amounts of many nutrients 
are unavailable or too limited to establish a UL and so the lack of a 
UL does not mean that the risk of adverse effects from high intake is 
nonexistent. Nutrient levels in commonly eaten foods rarely exceed 
the UL, although very highly fortified foods and dietary supplements 
provide more concentrated amounts of nutrients per serving and thus 
pose a potential risk of toxicity. Dietary supplements have Supplement 
Facts panels on labels that express the amount of nutrients present in 
absolute units or as the percentage of the DV provided per recom­
mended serving size. Total nutrient intakes, including that from foods, 
supplements, and over-the-counter medications (e.g., antacids), should 
not exceed RDA levels.
Chronic Disease Risk Reduction Intake (CDRR) 
The CDRR 
is the level above which a reduction in intake is expected to lower 
chronic disease risk is the CDRR. For example, the sodium CDRR for 
adults is 2300 mg/d; this is the lowest level of intake for which there is 
sufficiently strong evidence to characterize a CDRR. CDRRs are not 
available for potassium or other nutrients, but note that the AI for 
potassium was recently reduced to 2500 mg/d.
Acceptable Macronutrient Distribution Ranges (AMDRs) 

AMDRs are estimated ranges from epidemiologic data of energyproviding macronutrient intakes (protein, carbohydrate, and fat) 
considered to be healthful. These ranges are 10–35% of calories for 
protein, 20–35% of calories for fat, and 45–65% of calories for carbohy­
drate. Alcohol, which also provides energy, is not a nutrient; therefore, 
no recommendations for it are provided. The latest DRI committee

(μg/d)
CHOLINE 
(mg/d)g
Birth to 6 mo
400*
40*

4*
2.0*
0.2*
0.3*
2*
0.1*
65*
0.4*
1.7*
5*
125*
6–12 mo
500*
50*

5*
2.5*
0.3*
0.4*
4*
0.3*
80*
0.5*
1.8*
6*
150*
1–3 y

30*
0.5
0.5

0.5

0.9
2*
8*
200*
4–8 y

55*
0.6
0.6

0.6

1.2
3*
12*
250*
9–13 y

60*
0.9
0.9

1.0

1.8
4*
20*
375*
14–18 y

75*
1.2
1.3

1.3

2.4
5*
25*
550*
19–30 y

120*
1.2
1.3

1.3

2.4
5*
30*
550*
31–50 y

120*
1.2
1.3

1.3

2.4
5*
30*
550*
51–70 y

120*
1.2
1.3

1.7

2.4h
5*
30*
550*
>70 y

120*
1.2
1.3

1.7

2.4h
5*
30*
550*
9–13 y

60*
0.9
0.9

1.0

1.8
4*
20*
375*
14–18 y

75*
1.0
1.0

1.2
400i
2.4
5*
25*
400*
ACID (mg/d)
BIOTIN 

(lg/d)
PANTOTHENIC 
(lg/d)f
VITAMIN B12 
(mg/d)
FOLATE 
(mg/d)e
VITAMIN B6 
PART 10
Disorders of the Gastrointestinal System
(mg/d)
NIACIN 
TABLE 343-1  Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes for Vitamins
(mg/d)
RIBOFLAVIN 
(lg/d)
THIAMIN 
(mg/d)d
VITAMIN K 
(lg/d)b,c
VITAMIN E 
(mg/d)
VITAMIN D 
(lg/d)a
VITAMIN C 
GROUP
VITAMIN A 
LIFE-STAGE 

Children
Females
Infants
Males

aAs retinol activity equivalents (RAEs). 1 RAE = 1 μg retinol, 12 μg β-carotene, 24 μg α-carotene, or 24 μg β-cryptoxanthin. The RAE for dietary provitamin A carotenoids is twofold greater than the retinol equivalent (RE), whereas the RAE for 
bound B12, it is advisable for those >50 years of age to meet their RDA mainly by consuming foods fortified with B12 or a supplement containing B12. iIn view of evidence linking inadequate folate intake with neural tube defects in the fetus, it 
(SRR-, SSR-, SRS-, and SSS-α-tocopherol) also found in fortified foods and supplements. eAs niacin equivalents (NEs). 1 mg of niacin = 60 mg of tryptophan; 0–6 months = preformed niacin (not NE). fAs dietary folate equivalents 
intake level sufficient to meet the nutrient requirements of nearly all healthy individuals (97–98%) in a group. The RDA is calculated from an estimated average requirement (EAR). If sufficient scientific evidence is not available to establish 
is recommended that all women capable of becoming pregnant consume 400 μg of folate from supplements or fortified foods in addition to intake of food folate from a varied diet. jIt is assumed that women will continue consuming 400 μg 
an EAR and thus to calculate an RDA, an AI is usually developed. For healthy breast-fed infants, an AI is the mean intake. The AI for other life-stage and sex-specific groups is believed to cover the needs of all healthy individuals in those 
whether a dietary supply of choline is needed at all stages of the life cycle, and it may be that the choline requirement can be met by endogenous synthesis at some of these stages. hBecause 10–30% of older people may malabsorb foodpreformed vitamin A is the same as the RE. bAs cholecalciferol. 1 μg cholecalciferol = 40 IU vitamin D. cUnder the assumption of minimal sunlight. dAs α-tocopherol. α-Tocopherol includes RRR-α-tocopherol, the only form of α-tocopherol 
(DFEs). 1 DFE = 1 μg food folate = 0.6 μg of folic acid from fortified food or as a supplement consumed with food = 0.5 μg of a supplement taken on an empty stomach. gAlthough AIs have been set for choline, there are few data to assess 
Note: This table (taken from the DRI reports; see www.nap.edu) presents recommended dietary allowances (RDAs) in bold type and adequate intakes (AIs) in ordinary type followed by an asterisk (*). An RDA is the average daily dietary 
that occurs naturally in foods, and the 2R-stereoisomeric forms of α-tocopherol (RRR-, RSR-, RRS-, and RSS-α-tocopherol) that occur in fortified foods and supplements. It does not include the 2S-stereoisomeric forms of a-tocopherol 
Source: National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. https://doi.org/10.17226/25353. Adapted and reproduced with permission from the National Academy of 
19–30 y

90*
1.1
1.1

1.3
400i
2.4
5*
30*
425*
31–50 y

90*
1.1
1.1

1.3
400i
2.4
5*
30*
425*
51–70 y

90*
1.1
1.1

1.5

2.4h
5*
30*
425*
>70 y

90*
1.1
1.1

1.5

2.4h
5*
30*
425*
14–18 y

75*
1.4
1.4

1.9
600j
2.6
6*
30*
450*
19–30 y

90*
1.4
1.4

1.9
600j
2.6
6*
30*
450*
31–50 y

90*
1.4
1.4

1.9
600j
2.6
6*
30*
450*
14–18 y

75*
1.4
1.6

2.0

2.8
7*
35*
550*
19–30 y

90*
1.4
1.6

2.0

2.8
7*
35*
550*
31–50 y

90*
1.4
1.6

2.0

2.8
7*
35*
550*
from supplements or fortified food until their pregnancy is confirmed and they enter prenatal care, which ordinarily occurs after the end of the periconceptional period—the critical time for formation of the neural tube.
groups, but lack of data or uncertainty in the data makes it impossible to specify with confidence the percentage of individuals covered by this intake.
Sciences, Courtesy of the National Academies.
Lactating Women
Pregnant Women

(g/d)
CHLORIDE 
Birth to 6 mo
200*
0.2*
200*
0.01*
110*
0.27*
30*
0.003*
2*
100*
15*
2*
0.4*
0.12*
0.18*
6–12 mo
260*
5.5*
220*
0.5*
130*

75*
0.6*
3*
275*
20*

0.7*
0.37*
0.57*
(g/d)
9–13 y

21*

2*

1.6*

4.5*
1.5*
2.3*
>70 y

30*

4*

2.3*

4.7*
1.2*
1.8*
51–70 y

30*

4*

2.3*

4.7*
1.3*
2.0*
31–50 y

35*

4*

2.3*

4.7*
1.5*
2.3*
19–30 y

35*

4*

2.3*

4.7*
1.5*
2.3*
14–18 y

35*

3*

2.2*

4.7*
1.5*
2.3*
9–13 y

25*

2*

1.9*

4.5*
1.5*
2.3*
4–8 y

15*

1*

1.5*

3.8*
1.2*
1.9*
1–3 y

11*

0.7*

1.2*

3.0*
1.0*
1.5*
(g/d)
SODIUM 
(mg/d)
POTASSIUM 
(lg/d)
ZINC 
(mg/d)
SELENIUM 
(lg/d)
PHOSPHORUS 
(mg/d)
MOLYBDENUM 
TABLE 343-2  Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes for Elements
(mg/d)
MANGANESE 
(mg/d)
MAGNESIUM 
(lg/d)
IRON 
(mg/d)
IODINE 
(lg/d)
FLUORIDE 
(lg/d)
COPPER 
(mg/d)
CHROMIUM 
GROUP
CALCIUM 
LIFE-STAGE 

Children
Females
Infants
Males

intake level sufficient to meet the nutrient requirements of nearly all healthy individuals (97–98%) in a group. The RDA is calculated from an estimated average requirement (EAR). If sufficient scientific evidence is not available to establish 
an EAR and thus to calculate an RDA, an AI is usually developed. For healthy breast-fed infants, an AI is the mean intake. The AI for other life-stage and sex-specific groups is believed to cover the needs of all healthy individuals in those 
Note: This table (taken from the DRI reports; see www.nap.edu) presents recommended dietary allowances (RDAs) in bold type and adequate intakes (AIs) in ordinary type followed by an asterisk (*). An RDA is the average daily dietary 
Source: National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. https://doi.org/10.17226/25353. Adapted and reproduced with permission from the National Academy of 
31–50 y

45*

3*

2.6*

5.1*
1.5*
2.3*
19–30 y

45*

3*

2.6*

5.1*
1.5*
2.3*
14–18 y

44*

3*

2.6*

5.1*
1.5*
2.3*
31–50 y

30*

3*

2.0*

4.7*
1.5*
2.3*
19–30 y

30*

3*

2.0*

4.7*
1.5*
2.3*
14–18 y

29*

3*

2.0*

4.7*
1.5*
2.3*
>70 y

20*

3*

1.8*

4.7*
1.2*
1.8*
51–70 y

20*

3*

1.8*

4.7*
1.3*
2.0*
31–50 y

25*

3*

1.8*

4.7*
1.5*
2.3*
19–30 y

25*

3*

1.8*

4.7*
1.5*
2.3*
14–18 y

24*

3*

1.6*

4.7*
1.5*
2.3*
groups, but lack of data or uncertainty in the data makes it impossible to specify with confidence the percentage of individuals covered by this intake.
CHAPTER 343
Nutrient Requirements and Dietary Assessment 
Sciences, Courtesy of the National Academies.
Lactating Women
Pregnant Women

TABLE 343-3  Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes for Total Water and Macronutrients
LIFE-STAGE 

GROUP
TOTAL WATERa 
(L/d)
CARBOHYDRATE 
(g/d)
TOTAL FIBER 
(g/d)
Infants
Birth to 6 mo
0.7*
60*
NDc
31*
4.4*
0.5*
9.1*
6–12 mo
0.8*
95*
ND
30*
4.6*
0.5*
11.0
Children
1–3 y
1.3*

19*
ND
7*
0.7*

4–8 y
1.7*

25*
ND
10*
0.9*

Males
9–13 y
2.4*

31*
ND
12*
1.2*

14–18 y
3.3*

38*
ND
16*
1.6*

19–30 y
3.7*

38*
ND
17*
1.6*

31–50 y
3.7*

38*
ND
17*
1.6*

51–70 y
3.7*

30*
ND
14*
1.6*

>70 y
3.7*

30*
ND
14*
1.6*

Females
9–13 y
2.1*

26*
ND
10*
1.0*

14–18 y
2.3*

26*
ND
11*
1.1*

19–30 y
2.7*

25*
ND
12*
1.1*

31–50 y
2.7*

25*
ND
12*
1.1*

51–70 y
2.7*

21*
ND
11*
1.1*

>70 y
2.7*

21*
ND
11*
1.1*

Pregnant Women
PART 10
Disorders of the Gastrointestinal System
14–18 y
3.0*

28*
ND
13*
1.4*

19–30 y
3.0*

28*
ND
13*
1.4*

31–50 y
3.0*

28*
ND
13*
1.4*

Lactating Women
14–18
3.8*

29*
ND
13*
1.3*

19–30 y
3.8*

29*
ND
13*
1.3*

31–50 y
3.8*

29*
ND
13*
1.3*

Note: This table (taken from the DRI reports; see www.nap.edu) presents recommended dietary allowances (RDAs) in bold type and adequate intakes (AIs) in ordinary type 
followed by an asterisk (*). An RDA is the average daily dietary intake level sufficient to meet the nutrient requirements of nearly all healthy individuals (97–98%) in a group. 
The RDA is calculated from an estimated average requirement (EAR). If sufficient scientific evidence is not available to establish an EAR and thus to calculate an RDA, an AI 
is usually developed. For healthy breast-fed infants, an AI is the mean intake. The AI for other life-stage and sex-specific groups is believed to cover the needs of all healthy 
individuals in those groups, but lack of data or uncertainty in the data make it impossible to specify with confidence the percentage of individuals covered by this intake.
aTotal water includes all water contained in food, beverages, and drinking water. bBased on grams of protein per kilogram of body weight for the reference body weight 
(e.g., for adults: 0.8 g/kg body weight for the reference body weight). cNot determined.
Source: National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. https://doi.org/10.17226/25353. Adapted 
and reproduced with permission from the National Academy of Sciences, Courtesy of the National Academies.
recommended that the CDRR method be used instead of the AMDR 
for establishing DRIs for macronutrients in the future.
■
■FACTORS ALTERING NUTRIENT NEEDS
The DRIs are affected by age, sex, growth rate, pregnancy, lacta­
tion, physical activity level, concomitant diseases, drugs, and dietary 
composition.
Physiologic Factors 
Growth, strenuous physical activity, preg­
nancy, and lactation all increase needs for energy and several essential 
nutrients. Energy needs rise during pregnancy due to fetal growth 
demands and increased energy required for milk production during 
lactation. Energy needs decrease with loss of lean body mass, the major 
determinant of REE. The energy needs of older persons, especially 
those aged >70 years, tend to be lower than those of younger persons 
because lean tissue, physical activity, and health often decline with age.
Dietary Composition 
Dietary composition affects the biologic 
availability and use of nutrients. For example, iron absorption may be 
impaired by large amounts of calcium or lead; likewise, non-heme iron 
uptake may be impaired by a lack of ascorbic acid and amino acids in 
the meal. Bodily protein may be decreased when essential amino acids 

`-LINOLENIC ACID 
(g/d)
FAT 

(g/d)
LINOLEIC ACID 
(g/d)
PROTEINb 

(g/d)
are not present in sufficient amounts—a rare scenario in U.S. diets. 
Animal foods, such as milk, eggs, and meat, have high biologic values, 
with most of the needed amino acids present in adequate amounts. 
Plant proteins in corn (maize), soy, rice, and wheat have lower biologic 
values and must be combined with other plant or animal proteins or 
fortified with the amino acids that are deficient to achieve optimal use 
by the body.
Route of Intake 
The RDAs apply only to oral intakes. When nutri­
ents are administered parenterally, similar values can sometimes be 
used for amino acids, glucose (carbohydrate), fats, sodium, chloride, 
potassium, and most vitamins because their intestinal absorption rate 
is nearly 100%. However, the oral bioavailability of most mineral ele­
ments may be only half that obtained by parenteral administration. For 
some nutrients that are not readily stored in the body or that cannot be 
stored in large amounts, timing of administration may also be impor­
tant. For example, amino acids cannot be used for protein synthesis if 
they are not supplied together intravenously; instead, they will be used 
for energy production. In contrast, among healthy individuals eating 
adequate diets, the distribution of protein intake over the course of the 
day has little effect on health.

Disease 
Dietary deficiency diseases include protein-calorie malnu­
trition, iron-deficiency anemia, goiter (due to iodine deficiency), rick­
ets and osteomalacia (vitamin D deficiency), xeropthalmia (vitamin A 
deficiency), megaloblastic anemia (vitamin B12 or folic acid deficiency), 
scurvy (vitamin C/ascorbic acid deficiency), beriberi (thiamin defi­
ciency), and pellagra (niacin and tryptophan deficiency) (Chaps. 344 
and 345). Each deficiency disease is characterized by imbalances at the 
cellular level between the supply of nutrients or energy and the body’s 
nutritional needs for growth, maintenance, and other functions. Imbal­
ances and excesses in nutrient intakes are recognized as risk factors 
for certain chronic degenerative diseases, such as saturated/trans-fat 
and cholesterol in coronary artery disease; sodium in hypertension; 
obesity in hormone-dependent cancers (endometrial and breast); and 
ethanol in alcohol addiction. These disorders are multifactorial in their 
etiology and pathogenesis, and diet is only one of the many risk factors 
for their occurrence. Osteoporosis, for example, is sometimes associ­
ated with calcium deficiency secondary to vitamin D deficiency, as 
well as with environment-related risk factors (e.g., smoking, sedentary 
lifestyle), physiology (e.g., estrogen deficiency), genetic determinants 
(e.g., defects in collagen metabolism), and drug use (chronic steroids 
and aromatase inhibitors) (Chap. 423).
■
■DIETARY ASSESSMENT
Nutrition assessment in clinical situations is an iterative process 
involving screening for malnutrition risk; assessing the diet and other 
biomarkers to determine if malnutrition is present and if so its possible 
causes; planning and implementing appropriate dietary intakes and 
medical nutrition therapy; and reassessing to make sure that intakes 
have been consumed. Disease states affecting the bioavailability, 
requirements, use, or excretion of specific nutrients may require spe­
cific measurements of certain nutrients or their biomarkers to assess 
status and ensure that nutrient replacement is adequate (Chap. 344).
The Joint Commission, which accredits and certifies health care 
organizations in the United States, requires most health care facilities 
to perform nutrition screening for identifying possible malnutrition 
risk within 24 h after hospital admission. However, a single univer­
sally recognized or validated standard is not used yet. The Global 
Leadership Initiative on Malnutrition (GLIM) proposes that in acute 
care settings a tool be used that evaluates weight loss, low body mass 
index (BMI), reduced muscle mass, reduced food intake or absorption, 
and increased disease burden or inflammation. Other screens usually 
include these and also abnormal weight for height or body mass index 
(e.g., BMI <19 or >25); reported weight change (involuntary loss or 
gain of >5 kg in the past 6 months) (Chap. 50); diagnoses with known 
nutritional implications (e.g., metabolic disease, any disease affecting 
the gastrointestinal tract, alcohol abuse); present therapeutic dietary 
prescription; chronic poor appetite; presence of dental, chewing, and 
swallowing problems; major food allergies or intolerances; need for 
assistance with preparing or shopping for food, eating, or other aspects 
of self-care; and social isolation. The nutritional status of hospitalized 
patients should be reassessed periodically—at least once every week.
Patients who exhibit frank malnutrition or a high risk of it on nutri­
tional screening need more complete dietary assessment that varies 
with the clinical setting, the severity of the patient’s illness, and the 
stability of the patient’s condition.
Acute-Care Settings 
The goal is to identify and avoid inadequate 
intake, assure intake is appropriate, and gather enough information 
to determine if malnutrition is due to poor dietary intake or other 
causes and whether nutritional therapy is indicated (Chap. 346). In 
acute-care settings, anorexia, various diseases, test procedures, and 
medications can further compromise dietary intake. Dietary assess­
ment focuses on what patients are currently eating, whether or not 
they are able and willing to eat, and whether or not they experience 
any problems with eating. Simple observations may suffice to suggest 
inadequate oral intake. These include dietitians’ and nurses’ notes; 
observation of a patient’s frequent refusal to eat or the amount of food 
served versus that eaten on trays; the frequent performance of tests and 
procedures that are likely to cause meals to be skipped; consumption 

limited to nutritionally inadequate diet orders (e.g., clear liquids or full 
liquids) for more than a few days; the occurrence of fever, dehydra­
tion, gastrointestinal distress, vomiting, diarrhea, or a comatose state; 
and the presence of diseases or use of treatments that involve any part 
of the alimentary tract. Acutely ill patients with diet-related diseases 
such as diabetes and chronic renal failure are in particular need of 
assessment because an inappropriate diet may exacerbate these condi­
tions and adversely affect other therapies. Abnormal biochemical values 
(serum albumin levels <35 g/L [<3.5 mg/dL]; serum cholesterol levels 
<3.9 mmol/L [<150 mg/dL]) are nonspecific but may indicate a need for 
further nutritional assessment.

Most therapeutic diets offered in hospitals are calculated to meet 
individual nutrient requirements and the RDA if they are eaten. 
Exceptions include clear liquids, some full-liquid diets, and test diets 
(such as those adhered to in preparation for gastrointestinal proce­
dures), which are inadequate in several nutrients and should not be 
used, if possible, for >24 h. However, because as much as half of the 
food served to hospitalized patients is not eaten, it cannot be assumed 
that the intakes of hospitalized patients are adequate. Dietary assess­
ment should compare how much and what kinds of food the patient 
has consumed with the diet that has been provided. Major deviations 
in intakes of energy, protein, fluids, or other nutrients of special con­
cern for the patient’s illness should be noted and corrected, especially 
for long-staying patients.
Nutritional monitoring is especially important for patients who 
are very ill, who have extended lengths of hospital stay, or who are 
discharged home with diagnoses involving the gastrointestinal tract, 
end-stage renal disease, and insulin-dependent diabetes. Patients who 
are fed by enteral and parenteral routes and those receiving home 
chemotherapy infusions also require special nutritional assessment 
and monitoring by physicians and/or dietitians with certification in 
nutritional support (Chap. 346).
CHAPTER 343
Ambulatory Settings 
The aim of dietary assessment in the out­
patient setting is to determine whether or not the patient’s usual diet 
is a health risk in itself, if it contributes to existing chronic disease–
related problems, and if medical nutrition therapy is required. The 
information is used to plan an eating pattern that fulfills therapeutic 
goals while ensuring patient adherence. Dietary assessment should 
review the adequacy of present and usual food intakes, including 
vitamin and mineral supplements, oral nutritional supplements, 
medical foods, other dietary supplements, medications, and alcohol, 
because all of these may affect the patient’s nutritional status. Assess­
ment should focus on the dietary constituents that are most likely to 
be involved or compromised by the specific diagnosis as well as on 
any comorbidities that are present. A diet history of several days of 
intake or a food-frequency questionnaire can be used and reviewed to 
provide a representation of the usual diet and assess the adequacy of 
the patient’s habitual diet. The Automated Self-Administered 24-Hour 
Dietary Assessment Tool (ASA24) (which is a web-based, self-admin­
istered, 24-h recall tool), a diet history questionnaire (DHQ), a daily 
food checklist, and validated short dietary instruments are all available 
at the National Institute of Health’s National Cancer Institute webpage 
at https://epi.grants.cancer.gov/dietary-assessment/resources.html. The 
Nutritools interactive website (www.nutritools.org) guides clinicians 
and researchers to choose among suitable validated dietary assessment 
tools used in North America and elsewhere. Assessment findings are 
used to craft dietary recommendations for changes in healthier direc­
tions. These may be as simple as a food guide, a food-exchange list, or 
more personalized and detailed recommendations by a dietitian that 
are tailored to the patient’s food preferences and medical nutrition 
therapy needs. Therapeutic dietary prescriptions and menu plans for 
most diseases are available in the diet manuals of most hospitals and 
from the Academy of Nutrition and Dietetics for many other diseases. 
For persons on therapeutic diets, counseling using food-exchange 
lists such as those available from the American Diabetes Association 
for diabetes and from the Academy of Nutrition and Dietetics or the 
National Kidney Foundation’s Council on Renal Nutrition for renal 
disease is helpful. Patients who follow ethnic or unusual dietary 
Nutrient Requirements and Dietary Assessment

TABLE 343-4  Choose My Plate: A Guide to Individualized 

Dietary Planning
EXAMPLES OF STANDARD PORTION SIZES AT 
 
INDICATED ENERGY LEVEL
DIETARY FACTOR, UNIT OF 
MEASURE (ADVICE)
LOWER: 

1600 kcal
MODERATE: 
2200 kcal
HIGHER: 
2800 kcal
Fruits, cups (Focus on fruits.)
1.5

2.5
Vegetables, cups (Vary 
vegetables.)

3.5
Grains, oz eq (Make at least half 
of grains whole.)a

Protein foods, oz eq (Go lean 
with protein.)b

Dairy, cups or ozc (Choose 
calcium-rich foods.)

“Empty” calories, kcald

Sodium, mg
<2300 at all 
energy levels
 
 
Physical activity, min
At least 150 min vigorous physical activity per 
week at all energy levels
Note: Oils (formerly listed with portions of 5, 6, and 8 teaspoons for the lower, 
moderate, and higher energy levels, respectively) are no longer singled out in 
Choose My Plate, but rather are included in the empty calories/added sugar 
category with SOFAS (calories from solid fats and added sugars). The limit is 
the remaining number of calories in each food pattern above after intake of the 
recommended amounts of the nutrient-dense foods.
aFor example, 1 serving equals 1 slice bread, 1 cup ready-to-eat cereal, or 0.5 cup 
cooked rice, pasta, or cooked cereal. bFor example, 1 serving equals 1 oz lean meat, 
poultry, or fish; 1 egg; 1 tablespoon peanut butter; 0.25 cup cooked dry beans; or 
0.5 oz nuts or seeds. cFor example, 1 serving equals 1 cup milk or yogurt, 1.5 oz 
natural cheese, or 2 oz processed cheese. dFormerly called “discretionary calorie 
allowance.” Portions are calculated as the number of calories remaining after all of 
the above allotments are accounted for.
Abbreviation: oz eq, ounce equivalent.
Source: Data from U.S. Department of Agriculture (http://www.Choosemyplate.gov).
PART 10
Disorders of the Gastrointestinal System
patterns need extra instruction on how to categorize their foods and 
on the appropriate portion sizes that constitute a serving.
For healthy persons who do not require medical nutrition therapy, 
a rough guide for avoiding inadequate nutrient intakes as well as 
excessive intakes of fat (especially saturated and trans fats), sodium, 
sugar, and alcohol is the USDA’s Choose My Plate (Table 343-4). The 
Choose My Plate graphic emphasizes a balance between calories and 
nutritional needs, encouraging increased intake of fruits and veg­
etables, whole grains, and low-fat milk in conjunction with reduced 
intake of sodium and high-calorie sugary drinks. The guide provides 
a web-based calculator that tailors the number of servings suggested 
for healthy people of different weights, sexes, ages, and life-cycle stages 
to meet their needs while avoiding excess (https://www.myplate.gov/
myplate-plan and www.ChooseMyPlate.gov). Reviewing the guide with 
patients helps them identify food groups eaten in insufficient amounts 
or in excess and aids the transition to healthier dietary patterns.
■
■NUTRITIONAL STATUS ASSESSMENT
Full nutritional status assessment is reserved for seriously ill patients 
and those at very high nutritional risk when the cause of malnutrition 
is still uncertain after initial clinical evaluation and dietary assessment. 
It involves multiple dimensions, including documentation of dietary 
intake, health history, anthropometric measurements, biochemical 
measurements of blood and urine, clinical examination, and functional 
status evaluation. For further discussion of nutritional assessment, 
see Chap. 345.
■
■GLOBAL CONSIDERATIONS
Several DRIs (e.g., the EAR, the UL, and energy needs) are estimates 
of physiologic requirements based on experimental evidence that apply 
globally to healthy individuals when adjusted for age, sex, body size, 
and physical activity level. However, the AIs, AMDRs, and CDRRs are 
not exportable and should be used with caution in other countries. 

AIs for micronutrients are based on epidemiologic observations of 
customary and adequate intakes in healthy U.S. and Canadian popu­
lations. The AMDRs are not based on direct experimental evidence 
but represent expert opinion on potentially healthy intakes of energyproviding nutrients in North American populations. The CDRR may 
also vary in other populations. Nutrient-based standards like the 
DRIs have also been developed by the World Health Organization/
Food and Agricultural Organization of the United Nations. They are 
available at https://www.who.int/activities/establishing-global-nutrientrequirements. The European Food Safety Authority (EFSA) Panel 
on Dietetic Products, Nutrition, and Allergies periodically publishes 
its recommendations in the EFSA Journal (https://efsa.onlinelibrary.
wiley.com/journal/18314732). Other countries have also promulgated 
recommendations similar to the DRI. The different standards have 
many similarities in their basic concepts, definitions, and nutrient rec­
ommendation levels, but some differ from the DRIs as a result of the 
functional criteria chosen for nutrient requirements, environmental 
differences, the timeliness of the evidence reviewed, and expert judg­
ment. There is a growing trend toward global harmonization of these 
recommendations.
DISCLAIMER
The opinions expressed in this article are the author’s own and do not 
reflect the views of the National Institutes of Health, the U.S. Depart­
ment of Health and Human Services, or the U.S. government.
■
■FURTHER READING
Alves LF et al: GLIM criteria to identify malnutrition in patients 
in hospital settings: A systematic review. J Parenteral Enteral Nutr 
47:702, 2023.
Lewis JL, Dwyer JT: Establishing nutrient intake values, in Present 
Knowledge in Nutrition, Vol 2. BP Marriott, DF Birt, VA Stallings, AA 
Yates, eds. London, Academic Press, 2020, pp 267–289.
National Academy of Sciences, Engineering, and Medicine: 
Guiding Principles for Developing Dietary Reference Intakes Based on 
Chronic Disease. Washington, DC, National Academies Press, 2017.
National Academy of Sciences, Engineering, and Medicine: 
Dietary Reference Intakes for Sodium and Potassium. Washington, 
DC, National Academies Press, 2019.
National Academy of Sciences, Engineering, and Medicine: 
Harmonizing the Process for Establishing Nutrient Reference Values: 
A Tool Kit. Washington, DC, National Academies Press, 2020.
National Academy of Sciences, Engineering, and Medicine: 
Nutrition During Pregnancy and Lactation: Exploring New Evidence: 
Proceedings of a Workshop—in Brief. Washington, DC, National 
Academies Press, 2020.
National Academy of Sciences, Engineering, and Medicine: 
Approaches to assessing intake of food and dietary supplements in 
pregnant women and children 2 to 11 years of age: Proceedings of a 
workshop series. Washington, DC, National Academies Press, 2022.
National Academy of Sciences, Engineering, and Medicine: 
Defining populations for Dietary Reference Intake recommenda­
tions: A letter report. Washington, DC, National Academies Press, 
2022.
National Academy of Sciences, Engineering, and Medicine: 
Assessing intake of food and dietary supplements in older adults: 
Proceedings of a workshop series. Washington, DC, National Acad­
emies Press, 2023.
National Academy of Sciences, Engineering, and Medicine: 
Dietary Reference Intakes for Energy. Washington, DC, National 
Academies Press, 2023.
National Academy of Sciences, Engineering, and Medicine: 
Using systematic reviews to support future Dietary Reference Intakes: 
A letter report. Washington, DC, National Academies Press, 2023.
US Department of Agriculture and U.S. Department of Health 
and Human Services: Dietary Guidelines for Americans, 20202025, 9th ed. Washington, DC, US Government Printing Office, 
2020.