Basic Nutrition – LipidsDigestion, Absorption &

Metabolism

Outline – Dietary LipidsOutline – Dietary Lipids

1.Digestion2.Transport3.Metabolism4.Recommendations - DRI

Dietary LipidsDietary 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

What about lipid absorption?What about lipid absorption?

Brush bordermembrane

Basolateralmembrane

Fructose GlucoseGalactose

GlucoseGalactose

Na+

Na+

Na+

K+

Fructose

SGLT-1

GLUT5

Na+

K+ ATPase

GLUT2

Disaccharidases

Fructose GlucoseGalactose

Fructose GlucoseGalactose

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

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 ClassificationsDietary Fat Classifications

• Saturated Fats• Cis monounsaturated fatty

acids• Cis polyunsaturated fatty acids

– n-6 fatty acids– n-3 fatty acids

• Trans fatty acids

Fat DRIsFat 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 ValuesTotal Fat DRI Values

Function Age MalesRDA/AI g/d

FemalesRDA/AI g/d

AMDR(% total energy)

Energy source, allow for absorption of fat soluble vitamins

19-30 ND** ND 25-35

31-50 ND ND 25-35

50-70 ND ND 25-35

>70 ND ND 25-35

** Not Determinable

Estimating Fat RequirementsEstimating 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 AMDRsEstimated 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)• α-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)

Function Age MalesRDA/AI g/d

Females*RDA/AI g/d

AMDR(% total energy)

Component of cell membranes, skin health

19-30 17 12 5-10

31-50 17 12 5-10

50-70 14 11 5-10

>70 14 11 5-10

* Recommendations change for pregnant or lactating women

n-3 polyunsaturated fatty acids (α-linolenic acid)

n-3 polyunsaturated fatty acids (α-linolenic acid)

Function Age MalesRDA/AI g/d

Females*RDA/AI g/d

AMDR(% total energy)

Neurological development and growth

19-30

1.6 1.1 0.6-1.2

31-50

1.6 1.1 0.6-1.2

50-70

1.6 1.1 0.6-1.2

>70 1.6 1.1 0.6-1.2

* Recommendations change for pregnant or lactating women