Basic Nutrition – LipidsDigestion, Absorption & Metabolism :Basic Nutrition – LipidsDigestion, Absorption & Metabolism


Slide 2:Outline – Dietary Lipids Digestion Transport Metabolism Recommendations - DRI


Dietary Lipids :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


Slide 16:What about lipid absorption? Brush border membrane Basolateral membrane Fructose Glucose Galactose Glucose Galactose Na+ Na+ Na+ K+ Fructose SGLT-1 GLUT5 Na+ K+ ATPase GLUT2 Disaccharidases Fructose Glucose Galactose Fructose Glucose Galactose H2O H2O


Two mechanisms – passive diffusion and carrier-mediated uptake :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


Slide 18: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


Dietary Fat Classifications :Dietary Fat Classifications Saturated Fats Cis monounsaturated fatty acids Cis polyunsaturated fatty acids n-6 fatty acids n-3 fatty acids Trans fatty acids


Fat DRIs :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


Total Fat DRI Values :Total Fat DRI Values ** Not Determinable


Estimating Fat Requirements :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.


Estimated AMDRs :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


n-6 polyunsaturated fatty acids (linoleic acid) :n-6 polyunsaturated fatty acids (linoleic acid) * Recommendations change for pregnant or lactating women


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