Basic Nutrition Lipids Digestion, Absorption

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Basic Nutrition LipidsDigestion, Absorption
Metabolism
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Outline Dietary Lipids

• Digestion
• Transport
• Metabolism
• Recommendations - DRI

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Dietary Lipids

• Research focus on optimal fatty acid composition
  of the diet
• Importance of docosahexanoic acid and arachidonic
  acid
• Adults encouraged to limit saturated, trans fats,
  and be wary of energy density
• Triglyceride is prominent form in diet
• Dietary lipids must shift from aqueous to
  non-aqueous environment
• Digestion and absorption includes emulsification,
  hydrolysis, micellization and uptake by the
  enterocyte

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What about lipid absorption?
GLUT2
Fructose
GLUT5
Fructose Glucose Galactose
Fructose Glucose Galactose
Disaccharidases
Fructose Glucose Galactose
Na
K
Glucose Galactose
ATPase
SGLT-1
Na
K
Na
H2O
H2O
Na
Brush border membrane
Basolateral membrane
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Two mechanisms passive diffusion and
carrier-mediated uptake

• Uptake studies demonstrated saturable process
• Putative fatty acid transport proteins
• Plasma membrane fatty acid binding protein
• Megalin
• CD35
• Caveolin
• Family of fatty acid transporters
• Carriers likely most important when lipid
  concentration low

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• EAR - Meets the requirement of half the healthy
  individuals in life stage group
• RDA - Meets the requirement of 97-98 of the
  healthy individuals in life stage group (RDA
  EAR 2 SDrequirement)
• AI - Experimentally determined approximations
  for healthy individuals in life stage group
  (used when no RDA set)
• UL - Highest average daily nutrient intake level
  that is likely to pose no risk of adverse health
  effects

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Dietary Fat Classifications

• Saturated Fats
• Cis monounsaturated fatty acids
• Cis polyunsaturated fatty acids
• n-6 fatty acids
• n-3 fatty acids
• Trans fatty acids

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Fat DRIs

• Major fuel source for body
• Necessary for absorption of fat soluble vitamins
• Insufficient data to set RDA, AI, or UL for total
  fat
• Likewise, no RDA for saturated fat, n-9 cis
  monounsaturated fatty acids, trans fats
• AMDR is in place for total dietary fat intake

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Total Fat DRI Values
Not Determinable
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Estimating Fat Requirements

• Lack of clinical endpoints do not allow for
  setting EAR for total fat
• Saturated fatty acids can be synthesized as
  needed, no role in disease prevention
• Monounsaturated fatty acids have many functions,
  but can be synthesized
• n-6 Polyunsaturated fatty acids generally
  consumed well above deficiency level. AI
  evidence from total parenteral nutrition studies.

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Estimated AMDRs

• Set based on coronary heart disease (CHD) risk
  and obesity
• Linoleic acid
• AI, lower limit of AMDR set at 5 of energy
• Lack of evidence above 10 of energy (upper AMDR)
• a-linolenic acid
• AI is 0.6 of energy
• Upper AMDR is 1.2 of energy

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n-6 polyunsaturated fatty acids (linoleic acid)
Recommendations change for pregnant or
lactating women
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n-3 polyunsaturated fatty acids (a-linolenic
acid)
Recommendations change for pregnant or
lactating women