NATIONAL NUTRITION & PUBLIC HEALTH POLICIES:

Issues Related to Bioavailability of Nutrients When Developing & Using

Dietary Reference Intakes

Allison A. Yates, PhD, RDFood and Nutrition Board

Institute of MedicineThe National Academies

120-02

Examples of Applications of Reference IntakesUSERS:

• Government - Industry - Academia - Health Services

USES:• Guide for procuring food supplies for groups of

healthy persons• Basis for planning meals for groups• Reference point for evaluating the dietary intake of

population subgroups• Basis for food and nutrition education programs• Reference point for the nutrition labeling of food and

dietary supplements

261-01

Nutrition and Public Health Policy Formulation: Outline

DRI Framework/Process Development of DRIs Examples of Impact of Changes in

Bioavailability on Reference Values and Evaluation of Diets

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Recommended Dietary Allowances1989

Energy Protein 7 minerals (Ca, Fe, P, Mg, Zn, I, Se) 11 vitamins (A, C, D, B1, B2, niacin, E, K, B6,

B12, folate) Safe and adequate daily dietary intakes

(biotin, pantothenate, Cu, Mn, F, Cr, Mo)

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Dietary Reference Intakes

Upper Reference LevelsSubcommittee

Interpretation and Uses of DRIs

Subcommittee

Standing Committee on the ScientificEvaluation of Dietary Reference Intakes

Panels

Calcium, Vitamin D, Phosphorus, Mg, F--1997

Folate, B12, Other B Vitamins, Choline--1998

Vitamins A and K, B, Cr, Cu, Fe, I2, Mn, Mo, Ni, Si, V, Zn--2000

Energy and Macronutrients--2001

Electrolytes

149-04Other Food Components

Alcohol ?

Vitamins C and E, Se, ß-carotene and Other Carotenoids--2000

Major Points of DRI Framework

Based on estimating an average requirement Criteria used to assess adequacy Coefficient of variation of requirement often

extrapolated rather than measured Only use of RDA is as a goal for individual

365-01

Dietary Reference Intakes

Observed level of intake

UL

Ris

k of

inad

equa

cy Risk of excess0.5 0.5

RDA

AI

EAR

Increase 196-02

Dietary Reference Intakes

2 s.d.

Frequency Distributionof Individual Requirements

EAR

Increasing Intake

RDA

193-01

Dietary Reference Intakes

Observed level of intake

UL

Ris

k of

inad

equa

cy Risk of excess0.5 0.5

RDA

AI

EAR

Increase 196-02

To Provide a Quantitative Recommendation You Need:

Data on intakes/food composition Data from studies with multiple intakes and measured

indicators of adequacy Indicators which reflect status of individual, therefore

not rapidly resolved with increased intake Indicators correlated with health or functional outcome Both half-way point and coefficient of variation of

requirements needed to establish EAR and thus RDA

366-01

Bioavailability

Form of nutrient or food component Factors that affect absorption/utilization Assumptions for “typical” diet Special considerations

Bioavailability Assumptions for B12

DRI Recommended Intakes

Normal gastric, pancreatic, ileal function 50% average absorption of all forms of B12

10–30% of those > 50 y have atrophic gastritis

Percent Absorption of B12 from Foods, Healthy Adults

Foods Absorption (%)

Eggs 24 to 36

Chicken 60

Trout 25 to 47

Mutton 65

Liver 9

Source: Doscherholmen et al., 1975, 1978, 1981;Heyssel et al., 1966

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Requirements for Normal Absorption of Vitamin B12

Intact stomach Intrinsic factor Pancreatic sufficiency Functioning terminal ileum

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Effect of Oral Intake of B12 on Absorption

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Dose % Absorbed Amount Absorbed

1 µg 50 0.5 µg

5 µg 20 1.0 µg

25 µg 5 1.25 µg

Adams et al., Scand. J. Gastroenterol 6:249-252, 1971.

Derivation of EAR for B12

Requirement normal person for absorbed B12 = 1.0 µg/day

Correct for bioavailability 0.50 = 2.0µg/day

EAR: Average requirement for normal person for B12 from food - 2 µg/day

RDA for Vitamin B 12 (g/day)

Men and Women, 19 y + 2.4 g*

Pregnancy 2.6 g

Lactation 2.8 g

*For those over age 50 y, needs to come primarily from fortified foods or supplements

Distribution of Reported Vitamin B12 Intake for Men and Women Aged

19+ Years

05

101520253035404550

0 2 4 6 8 10 12 14 16 18 20 22 24

Males

FemalesPe

rce

nt

Vitamin B12 (µg)

EAR

Source: NHANES III, 1988–1994 (J. Wright) 389-01

SUMMARYBioavailability Assumptions for B12

DRI Recommended Intakes

Normal gastric, pancreatic, ileal function 50% average absorption of all forms of B12

10–30% of those > 50 y have atrophic gastritis

Bioavailability Assumptions for FolateDRI Recommended Intakes

Absorption of synthetic folate 1.7 - 2.0 x food folate

Folate supplements taken w/water 90% absorption Folate added to food or taken w/food 85% absorption Folate naturally found in food 50% absorption

Concept ofDietary Folate Equivalents

1 µg DFE = 0.5 µg folate from supplements

(DFE = 2 x weight)

= 0.6 µg folate from fortified food

(DFE = 1.7 x weight)

= 1.0 µg naturally present folate in food

(DFE = 1 x weight)

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Distribution of Reported Folate Intake for Men and Women Aged 19+ Years

0

5

10

15

20

25

30

35

40

0 200 400 600 800 1000

Males

FemalesPe

rce

nt

Folate (µg)

EAR

Source: NHANES III, 1988–1994 (J. Wright) 388-01

Distribution of Reported Folate Intake for Men and Women Aged 19+

Years, with Higher Bioavailability

0

5

10

15

20

25

30

35

40

0 200 400 600 800 1000

Males

FemalesPe

rce

nt

Folate (µg)

EARF

Source: NHANES III, 1988–1994 (J. Wright) 388-01

EARC

Importance of Data on Food Composition and Dietary Intake

Folate intakes in surveys underestimated due to:

Inadequate enzymatic digestion of food folate when determining food folate content

Data on intake based on prefortification values for folate content in foods consumed

Folate content of foods not available in DFEs Underreporting errors

Estimated Folate Intakes, 19-30 Years

05

1015202530354045

Men

Women

0

5

10

15

20

25

30

35

40

45

Unmodified DataNHANES III

Modified DataNHANES III

Pe

rce

nta

ge

of P

op

u la

ti on

µg DFE

403-01Lewis et al., 1999, AJCN, 70:198-207

µg

EAR

EAR

SUMMARYBioavailability Assumptions for Folate

DRI Recommended Intakes

Absorption of synthetic folate 1.7 - 2.0 x food folate

Folate supplements taken w/ water 90% absorption Folate added to food or taken w/food 85% absorption Folate naturally found in food 50% absorption

Bioavailability Assumptions for Iron 1989 RDA

Increased absorption with increased need Form of iron: heme vs non-heme Other food components

— Ascorbic acid — Phytate

— Polyphenols — Fiber

Typical diet “relatively highly available”, 10–15%

Prevalence of Inadequate Intakes 1989 Iron RDA

Men Women Need: Absorbed iron 1.3 mg 1.8 mg Intake: 10% absorption 13 mg 18 mg

15% absorption 8.7 mg 12 mg

RDA (12.5 %) 10 mg 15 mg NHANES III 19-30 y, inadequate <5% < 25%

Plant-based Diet, low in Vitamin CAdjustment of Iron RDA

Men Women

Need: Absorbed iron 1.3 mg 1.8 mg

Intake: Assume 4% absorption 32 mg 45 mg

NHANES III 19-30 y, inadequate 92% >95%

SUMMARYBioavailability Assumptions for Iron

1989 RDA

Increased absorption with increased need Form of iron: heme vs non-heme Other food components

— Ascorbic acid — Phytate

— Polyphenols — Fiber

Typical diet “relatively highly available”, 10–15%

Derivation of 1989 RDA for Protein

EAR ~ 0.6 g reference protein/kg/day CV ~ 12.5%

Need 0.75 g reference protein/kg/day

U.S. diet amino acid score ~ 100 for adults

U.S. digestibility ~ 100% RDA for men and women (rounded)

0.8 g protein/kg/day

Bioavailability Assumptions for Protein 1989 RDA

U.S. Diet high quality protein, amino acid score of 100 for adults

65% animal origin protein, 35% plant Digestibility 100 (equal to reference proteins) 14–18% of kcal from protein

Adjusting the 1989 RDA for Proteinfor a Primarily Plant-Based Diet, Adult

EAR ~ 0.6 g reference protein/kg/day CV ~ 12.5%

Need 0.75 g reference protein/kg/day

U.S. diet amino acid score ~ still 100 for adults

U.S. digestibility ~ 92% Adjusted RDA for men and women:

0.75 0. 92 = 0.8 g protein/kg/day

no change

Impact of 1/3 Animal, 2/3 Plant-Based Protein Diet, 3 yr Old

3 yr old amino acid score ~ 51/58 = 88 (due to low lysine content)

Digestibility ~ 92% Adjusted RDA for 3 yr old:

1.1g /kg 0.88 = 1.25 g/kg

1.25g/kg 0.92 = 1.36 g/kg

Adjusted RDA = 1.4 g protein/kg/day

27% increase in amount needed

SUMMARYBioavailability Assumptions for Protein

1989 RDA

U.S. diet high quality protein, amino acid score of 100 for adults

65% animal origin protein, 35% plant Digestibility 100 (equal to reference proteins) 14–18% of kcal from protein

Examples of Applications of RDAsUSERS:

• Government - Industry - Academia - Health Services

USES:• Guide for procuring food supplies for groups of

healthy persons• Basis for planning meals for groups• Reference point for evaluating the dietary intake of

population subgroups• Component of food and nutrition education

programs• Reference point for the nutrition labeling of food and

dietary supplements

261-01

Food and Nutrition Boardhttp://www.nas.edu/iom/fnb

Publications: http://www.nap.edu

111-02