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Thomas O. Henderson, Ph. D. Professor Emeritus Dept. of Biochemistry & Molecular Genetics Office: 321 CMW Phone: 6-5978 email: [email protected]

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Thomas O. Henderson, Ph. D. Professor Emeritus Dept. of Biochemistry & Molecular Genetics Office: 321 CMW Phone: 6-5978 email: [email protected] Macronutrients. Lecture 2 Carbohydrates & Fiber Lecture 3 Fats (Lipids) Lecture 4 Proteins. From MMWR 53 , No. 4; February 6, 2004.

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slide1

Thomas O. Henderson, Ph. D.

  • Professor Emeritus
  • Dept. of Biochemistry &
  • Molecular Genetics
macronutrients
Macronutrients
  • Lecture 2 Carbohydrates & Fiber
  • Lecture 3 Fats (Lipids)
  • Lecture 4 Proteins
macronutrients i
Macronutrients I
  • Overview
  • Carbohydrates
  • Fiber
2002 iom fnb guidelines for macronutrients
2002 IOM-FNB Guidelines for Macronutrients
  • 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 distribution range amdr
Acceptable Macronutrient 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
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 continued1
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 continued2
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
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
carbohydrates
Carbohydrates
  • 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
slide12
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 carbohydrates
Major Sources of 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)
slide15

Forms of Starch

Amylose

Amylopectin

Cellulose

(NOT a form

of starch)

slide16

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 concentration of hexoses in blood
Consequences of chronic elevation in concentration 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 alcohols
Sugar Alcohols
  • 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
slide20
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
slide22

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
galactose metabolism
Galactose 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
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
2 types of galactosemia are caused by deficiency or absence of:

D-galactose 1-P uridyltransferase and galactokinase

  • 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
slide27

Definitions:

Incidence = 1 in n live births

Prevalence = 1 in n people

the pathologies associated with defective d galactose 1 p uridyl transferase include
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 metabolism
Fructose 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
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
slide32

Essential Fructosuria

Fructose Intolerance

slide34

“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
slide36
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 gi
Factor Influencing GI

Number 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
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 intake of carbohydrates (and monounsaturated fat) should be individualized for each diabetic patient
dietary fiber
Dietary 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 fiber
Viscous 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
slide41
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
slide42
Viscous fibers includes pectins, various gums, mixed-linkage -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
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