Macronutrients IIMacronutrients II

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FatsFats

Triacylglycerol (TAG) (triglyceride)

• Fat, primarily TAG, currently provides ~34% of total calories in average American diet

• TAG also serve as major energy reserve in human tissues

Energy Reserves of Humans After 12hr Energy Reserves of Humans After 12hr FastFast

Fuel reservesStored fuel Tissue (g) (kcal)

Glycogen Liver 70 280 Glycogen Muscle 120 480Glucose Body fluids 20 80Fat Adipose 15,000 135,00Protein* Muscle 6,000 24,000Data are for “normal” male subject weighing 70 kg. Carbohydrate, 4 kcal/g; Fat, 9 kcal/g; Protein, 4 kcal/g*There is no specific storage form of protein

DRI’s for FatDRI’s for Fat

• Except for infants, 2002 IOM-FNB recs set no DRI for total fat intake

• This is because humans can synthesize saturated and unsaturated fatty acids and cholesterol and therefore are not required in diet

• Adequate Intakes (AI) for infants 0 - 6 and 7 - 12 months are 30 and 31 g/day, respectively

• Will deal with AI for n-6 & n-3 later in this lecture

Fat Consumption in the United States1900 ~20% of calories1960’s ~40 - 42%mid 1980’s ~38%Current ~34%2002 recs 20 - 35%

• In 1900, butter and lard comprised ~75% of fat intake

• This has been replace to a great extent by vegetable oils, margarine, and shortening

• This has led to increase in proportion of unsaturated fatty acids (especially linoleic acid) to saturated fatty acids in American diets

• Consequence of increased use of vegetable

oils has been increased amount of trans fatty

acids in the diet to ~2.6% of total energy

intake

• Trans fatty acids produced by partial

hydrogenation of vegetable oils during

production of margarines and shortening

A doughnut contains ~6 g trans fatty acids and a large order of fast-food french fries contains ~7 g trans fatty acids.

Oreo® cookies contain 2 g trans fatty acid per serving of 3 cookies

From Lichtenstein, A. H. et al., New England Journal of Medicine 25 :

1933 (1999)

See p. 8 Lipids Handout

• By far major sources of trans fatty acids in

diet include anything prepared with partially

hydrogenated vegetable oil or vegetable

shortening (e.g. Crisco®)

• Note that current food labels do not list trans

fatty acids

• In November 1999 U. S. FDA proposed that

trans fats be added to food labels

• In July 2003 FDA issued final rules on trans

fat labeling, to take effect January 2006

• One type of food label

showing amount of trans

fat, effective January 2006

• Some manufacturers

starting to use this type of

label now, especially if no

trans fat in the product

Effect of Effect of TransTrans Fatty Acids Fatty Acids on Serum Cholesterol Levelson Serum Cholesterol Levels

• Convincing evidence that trans fatty acids

increase LDL:HDL ratios

• Indeed, they appear to increase the ratio

more than do saturated fatty acids

• They not only increase LDL, they also

markedly lower HDL

A Very Brief Review A Very Brief Review

ofof

Fat DigestionFat Digestion

and Absorptionand Absorption

pancreaticlipase

Orlistat(Xenical™)

• Inhibits pancreatic lipase• Undigested TAG excreted in feces• (Reduces fat absorption by ~20 - 30%)• Requires prescription

• Another compound, not to be confused with Orlistat®, is Olestra®

• Olestra® is a non-digestible sucrose-fatty acid polyester that can replace fat in prepared foods

• Use has thus far been limited to use in snack foods (potato chips, etc.) by FDA

• Both Orlistat and Olestra have some untoward GI side effects

• Vitamin A supplementation is required when either is used

R

R R

R R

R R

R

C-(CH2)n-CH3 = R

O

Sucrose polyester, also called Olestra®

Fatty acids not removed by pancreatic lipase

Approved by FDA for use in snack foods

Serum Lipoprotein Classes

Chylomicrons

Very Low Density Lipoprotein VLDL

Intermediate Density Lipoprotein IDL

Low Density Lipoprotein LDL

High Density Lipoprotein HDL

Ketone Body MetabolismKetone Body Metabolism• Ketone bodies (acetone, acetoacetic acid,

-hydroxybutyrate) produced in liver during fast or reduced carbohydrate take

• Incomplete fatty acid oxidation (and TCA operation) leads to increased acetyl-CoA concentration

3 acetyl-CoA HMG-CoA ketone bodies

• The liver cannot use ketone bodies.

• They are exported to extrahepatic tissues, many of which can use them readily as fuel

Glucagon

Essential Fatty Acids Essential Fatty Acids (PUFA)(PUFA)

• Linoleic acid (18:29,12) (n-6; 6)

• -Linolenic acid (18:39,12,15) (n-3; 3)

• Humans can synthesize arachidonic acid(20:45,8,11,14)(n-6; 6) from linoleic acid

• AI for n-6 PUFA as linoleic acid for adults ages19-50 is 19g/day; AMDR is 5-10% of daily caloriefor ages 1-70

• AI for n-3 PUFA as -linolenic acid acid for adults ages 9-70 is 1.1g/day; AMDR is 0.6-1.2% of daily calories for ages 1-70

indicates essential fatty acids

Humans can make from linoleate

Humans can make from linolenate

Various NSAIDs aspirin indomethacin ibuprofen

-

Anti-inflammatorycorticosteroids

-

Linoleate derivatives involved in water-proofing skin

Essential Fatty Acid Deficiency

Clinical deficiency ofessential fatty acidsrare on most normaldiets.

This individual wason prolonged EFA-freeTotal parenteral nutrition

Essential Fatty Acid Deficiency

Dermatosis resolvedfollowing two-weeksadministration of EFA

Low fat dietLow fat dietvsvs

Right fatRight fat

Olive oil dietfat = 41% of calories

Complex carb dietfat = 22% of calories