Define

1
NATIONAL NUTRITION PUBLIC HEALTH
POLICIES Issues Related to Bioavailability of
Nutrients When Developing Using Dietary
Reference Intakes
Allison A. Yates, PhD, RD Food and Nutrition
Board Institute of Medicine The National
Academies
120-02
2
Examples of Applications of Reference Intakes

• USERS
• 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

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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
Standing Committee on the Scientific Evaluation
of Dietary Reference Intakes
Panels
Calcium, Vitamin D, Phosphorus, Mg, F--1997
Folate, B12, Other B Vitamins, Choline--1998
Interpretation and Uses of DRIs Subcommittee
Upper Reference Levels Subcommittee
Vitamins C and E, Se, ß-carotene and Other
Carotenoids--2000
Vitamins A and K, B, Cr, Cu, Fe, I2, Mn, Mo, Ni,
Si, V, Zn--2000
Energy and Macronutrients--2001
Electrolytes
Other Food Components
Alcohol ?
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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

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Dietary Reference Intakes
EAR
UL
RDA
AI
Risk of excess
Risk of inadequacy
0.5
0.5
Observed level of intake
Increase
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Dietary Reference Intakes
Frequency Distribution of Individual Requirements
EAR
RDA
2 s.d.
Increasing Intake
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Dietary Reference Intakes
EAR
UL
RDA
AI
Risk of excess
Risk of inadequacy
0.5
0.5
Observed level of intake
Increase
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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

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Bioavailability

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

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Bioavailability Assumptions for B12 DRI
Recommended Intakes

• Normal gastric, pancreatic, ileal function
• 50 average absorption of all forms of B12
• 1030 of those gt 50 y have atrophic gastritis

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Percent Absorption of B12 from Foods, Healthy
Adults
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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
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 6249-252, 1971.
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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

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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

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Distribution of Reported Vitamin B12 Intake for
Men and Women Aged 19 Years
EAR
Percent
Vitamin B12 (µg)
Source NHANES III, 19881994 (J. Wright)
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SUMMARYBioavailability Assumptions for B12 DRI
Recommended Intakes

• Normal gastric, pancreatic, ileal function
• 50 average absorption of all forms of B12
• 1030 of those gt 50 y have atrophic gastritis

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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

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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
EAR
Percent
Folate (µg)
Source NHANES III, 19881994 (J. Wright)
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Distribution of Reported Folate Intake for Men
and Women Aged 19 Years, with Higher
Bioavailability
EARC
EARF
Percent
Folate (µg)
Source NHANES III, 19881994 (J. Wright)
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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

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Estimated Folate Intakes, 19-30 Years
EAR
Unmodified Data NHANES III
Percentage of Population
µg
EAR
Modified Data NHANES III
µg DFE
Lewis et al., 1999, AJCN, 70198-207
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SUMMARYBioavailability 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

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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, 1015

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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 lt5 lt 25

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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 gt95

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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, 1015

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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

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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)
• 1418 of kcal from protein

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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

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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

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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)
• 1418 of kcal from protein

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Examples of Applications of RDAs

• USERS
• 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
37
Food and Nutrition Boardhttp//www.nas.edu/iom/fn
bPublications http//www.nap.edu
111-02