Thomas O. Henderson, Ph. D.Thomas O. Henderson, Ph. D.

Professor EmeritusProfessor Emeritus

Dept. of Biochemistry & Dept. of Biochemistry &

Molecular GeneticsMolecular Genetics• Office:Office: 321 CMW321 CMW• Phone:Phone: 6-59786-5978• email: revtotis@uic.eduemail: revtotis@uic.edu

MacronutrientsMacronutrients

• Lecture 2 Lecture 2 Carbohydrates & FiberCarbohydrates & Fiber

• Lecture 3Lecture 3 Fats (Lipids)Fats (Lipids)

• Lecture 4Lecture 4 ProteinsProteins

From MMWR 53, No. 4; February 6, 2004

Macronutrients IMacronutrients I

• OverviewOverview• CarbohydratesCarbohydrates• FiberFiber

2002 IOM-FNB Guidelines for 2002 IOM-FNB Guidelines for MacronutrientsMacronutrients

• Goal of new recommendation “to meet the body’s daily energy and nutritional needs while minimizing risks for chronic disease.”

• Guidelines set for macronutrients: carbohydrates, fats, proteins

• For first time, DRI’s set for dietary fiber and essential fatty acids (n-3 & n-6)

• Guidelines set for exercise

Acceptable Macronutrient Acceptable Macronutrient Distribution Range (AMDR)Distribution Range (AMDR)

• AMDR just another way of stating the % of calories from a given class of macronutrient

• 2002 recs adults ≥19 years:

% of daily calories

Carbohydrates 45 - 65

Fats 20 - 35%

Proteins 10 - 35% ≤25% of total calories from “added sugar”

AMDR (continued)

• Recommendations more flexible than in past

• Ranges set so that total dietary intake would be of breadth and quality to insure intake of essential nutrients (i.e., vitamins & minerals)

• Diets very low in either carbs or fat likely to be deficient in one or more essential nutrient

AMDR (continued)

When fat intakes are low and carb intake is

high:

• HDL is reduced

• ratio of plasma cholesterol:HDL increased

• plasma triacylglycerol (TAG) increased

These all consistent with increased risk of

coronary heart disease (CHD; CAD)

AMDR (continued)

• When fat intakes are high, people gain weight

• Can exacerbate health of persons already susceptible to obesity, particularly risk of CHD and Type II diabetes

• High fat diets usually associated with increased intake of saturated fatty acids

• The latter, in turn, can increase LDL levels and thereby increase risk of CHD

All Fatty Acids are NOT Equal!

If fat intake is at high end of 20 -35%

range, one would be well advised to

• limit intake of cholesterol and

saturated and trans fatty acids

• replace them with monounsaturated

and polyunsaturated fatty acids

CarbohydratesCarbohydrates• 2002 IOM-FNB report set RDA for intake of

digestible carbohydrate

• for ages 1 - >70, 130 g/d recommended

• 175 & 210 g/d for lactating and pregnant women, respectively

• for 0 - 6 months, AI set at 60 g/d

• for 7 - 12 months, AI set at 95 g/d

• RDA (& AI) for carbs based on minimum amount needed to provide glucose for brain function

• Most of us regularly exceed RDA

• AMDR set at 45 - 65% of calories/day

• No more than 25% of calories/day from “added sugars”

• Emphasis should be on obtaining bulk of daily carbs from fruits, vegetables, and minimally processed whole grains and whole grain products

Major Sources of Major Sources of Carbohydrates Carbohydrates

• disaccharides (sucrose, lactose)

• starch (amylose & amylopectin)

• minor, variable amounts of glycogen (in meats), maltose, trehalose (mushrooms), raffinose (legumes)

• very little monosaccharide in natural diet

• increased amounts of added fructose (high-fructose corn syrup or solids)

MALTOSE SUCROSE

LACTOSE

Glu α(1 → 4) Glu Glu α(1 → 2) Fru

Gal β(1 → 4) Glu

Amylose

Amylopectin

Cellulose(NOT a form

of starch)

Forms of Starch

On a Food Label, Sugars Include:

brown sugar invert sugar

corn sweetener lactose

corn syrup maltose

fructose molasses

fruit juice concentrate raw sugar

glucose (dextrose) [table] sugar (sucrose)

high-fructose corn syrup syrup

honey

Consequences of chronic elevation in Consequences of chronic elevation in concentration of hexoses in bloodconcentration of hexoses in blood

2 possible consequences are

• enzymatic formation of sugar alcohols

• nonenzymatic glycosylation (“glycation”)

of proteins

Both of these associated with long term

pathologies of nerves, blood vessels,

kidneys, and lens as found in diabetes and

galactosemia

Sugar Sugar AlcoholsAlcohols

• Aldose reductase and polyol

dehydrogenase involved

• Isozymes of aldose reductase found in most

tissues

• Especially high in Schwann cells of

peripheral nerves, kidney papillae, and lens

epithelium

Ways in which sugar alcohols cause cell

damage and pathologies not known

However, since they do not diffuse out of

cells very readily, they can cause cell

damage by cellular swelling associated with

osmosis

The enzymatic reactions are reversible so

that favored direction is determined by

substrate/product concentrations (i. e.,

“mass action”)

Protein glycosylation (glycation)Protein glycosylation (glycation)

• nonenzymatic process

• get advanced glycosylation product

formation (“AGE products”) with

proteins

• quite possible that glycosylation of

DNA occurs also

An estimate of how well a diabetic patient has controlled her/his hyperglycemia over past 5-6 weeks can be made by measuring extent of hemoglobin glycosylation (HbA1c)

• Recall - RBC hemoglobin has lifespan of

~120 days

• Shorter or more recent periods can be

estimated by measuring albumin

glycosylation

Glucose

Protein

Schiff BaseAmadoriProduct

(more stable)

Glucose-DerivedCross-Link

(one kind of product)

Aminoguanineinhibits

Galactose MetabolismGalactose Metabolism

• By far major source of galactose in human

diet is in form of lactose

• Major source of lactose is milk and milk

products

• Major organ involved in galactose

metabolism is liver

• There are several inborn errors involving

metabolism of galactose

Lactase deficiency (aka Hypolactasia)(lactose or milk intolerence)

• In most mammals, including the great majority of humans, lactase activity disappears after weaning or at the latest during adolescence.

• In the case of humans, especially true for Southeast Asians and Africans.

• About 70% of African-Americans, >80% of Chinese and >70% of Mexicans are lactose intolerant

• In contrast, lactase deficiency uncommon in Northwest Europeans such as Scandinavians (~3% of Danes)

2 types of galactosemia are caused by deficiency or absence of:

D-galactose 1-P uridyltransferase D-galactose 1-P uridyltransferase and

galactokinasegalactokinase

• The first more common (prevalence = 1 in 70,000) than second (prevalence = 1 in 1 x 105) and has far greater clinical importance in terms of associated pathologies, especially in homozygotes

• In Illinois the incidence of the first defect is ~1 in 30,000 live births

Definitions:

Incidence = 1 in n live births

Prevalence = 1 in n people

The pathologies associated with defective D-galactose 1-P uridyl transferase include:

• severe mental retardation, hepatomegaly, cataracts, and non-specific morphological changes in the CNS

• In Illinois, all newborns are screened for galactosemia

• Affected infants MUST be placed on a galactose-free (i. e., milk-free) diet immediately to prevent irreversible damage

Fructose MetabolismFructose Metabolism

• Major sources of fructose in diet are fruits,

honey, sucrose and, now, in form of high

fructose corn syrup or solids as an added

sweetener in soft drinks, candy, etc.

• Fructose -in one form or another- may

account for 30 - 60% of total dietary

carbohydrates for some

• Major organ involved in fructose metabolism

is the liver

There are two (rare) inherited diseases of fructose metabolism

• Essential fructosuria - caused by deficiency in fructokinase and leads to transitory elevation of blood fructose level and to fructosuria (fructose in the urine)

• Fructose intolerance - MUCH MORE SERIOUS EFFECTS similar to those associated with galactosemia - caused by a defect in fructose-1-P aldolase (aldolase B)

• In fructose intolerance fructose and its sources (sucrose!) must be eliminated from diet

Essential Fructosuria

Fructose Intolerance

“Baby Bottle” Caries

“Baby Bottle” Caries. Rampant caries due to use of sugar-sweetened beverages in nursing bottle as a pacifier

From Nutrition in Clinical Dentistry, 3/ed, 1989, A. E. Nizel and A. S. Papas (W. B. Saunders), Fig. 3-7, p. 46.

Glycemic Index (GI)Glycemic Index (GI)Glycemic index of a carbohydrate defined

as incremental area under blood glucose

response curve of a 50g carbohydrate

portion of a test food expressed as a

percentage of the response to the same

amount of carbohydrate from a standard

food (usually glucose or white bread) taken

by the same subject.

An abbreviated table of GI’s found on

p. 8 of Macronutrient I handout

• In general, carbohydrate-containing foods such as whole grains, legumes, fruits, vegetables have low GI’s

• Amylose form of starch has lower GI than amylopectin

• Broadly speaking about grain products, the greater the processing, the higher the GI

Factor Influencing GIFactor Influencing GINumber of factors influence GI besides amount or type of carbohydrate in a meal.

In a multi-component food or meal, these include:

amount & type of carbohydrate

nature of starch

presence or absence of fat, protein, fiber

how food was prepared

Table of factors influencing GI found on p. 8 of Macronutrient I handout

Diabetes Care 27, Supplement 1,pp. S36 - S46, January 2004

American Diabetes Society issued Position Statement entitled “Evidence-Based Nutrition Principles and Recommendations for the Treatment and Prevention of Diabetes and Related Complications”

• The panel concluded, “If there are long term effects (of carbohydrate intake) on glycemia and serum lipids, these effects appear to be modest.”

• Their position is that recommendations on intakeof carbohydrates (and monounsaturated fat)should be individualized for each diabetic patient

Dietary FiberDietary Fiber• Defined as nondigestible carbohydrates &

lignin intrinsic and intact in plants

• Functional fiber defined as isolated nondigestible carbohydrates that have been shown to have beneficial effects in humans

• Total fiber: dietary fiber + functional fiber

• AI 38g/d for men ages 14 - 50 y; 25g/d for women ages 19 - 50 y

Tables for Total Fiber DRI (AI) and sources of fiber on p. 9, Macronutrient I handout

Viscous FiberViscous Fiber

• Some types of fiber form highly viscous solutions (viscous fiber)

• Viscous fibers delay gastric emptying of ingested foods into small intestine

• This produces sensation of fullness

• Delayed gastric emptying also results in reduced postprandial blood glucose levels

• Intake of even moderate amounts of viscous fiber is associated with lowering plasma cholesterol levels

• They apparently interfere with absorption of dietary fat and cholesterol and enterohepatic circulation of bile acids and cholesterol

• Viscous fibers includes pectins, various gums, mixed-linkage β-glycans, psyllium, agar, and carrageenan

• Oat bran, barley, legumes and various vegetables are good sources of viscous fiber

• Isolated fibers or fiber sources that are not viscous (e.g., cellulose, corn and wheat bran) rarely found to lower plasma cholesterol levels