BCH 282

Biochemistry of Nutrition

Objectives:

• To define nutrition and related words.To define nutrition and related words.

• To identify nutritional requirements.To identify nutritional requirements.

• To understand Food pyramid.To understand Food pyramid.

• To list types of nutrients and relation to health.To list types of nutrients and relation to health.

• To define malnutrition and its classification.To define malnutrition and its classification.

• To list main malnutrition problems. To list main malnutrition problems.

• To describe Obesity.To describe Obesity.

• NutritionNutrition is defined as the science of is defined as the science of

food and its relationship to health. Or, food and its relationship to health. Or,

• The process of making use of food.The process of making use of food.

• It is concerned primarily with the part It is concerned primarily with the part

played by nutrients in body growth, played by nutrients in body growth,

development and maintenance .development and maintenance .

• Dietetics is the practical application of the principles of nutrition; it includes the planning of meals for the well and the sick.

• Good nutrition means “maintaining a nutritional status that enables us to grow well and enjoy good health.”

• Nutrients are substances (specific dietary

constituents) that are crucial for human life,

growth & well-being.

• Macronutrients (carbohydrates, lipids, proteins &

water) are needed for energy and cell

multiplication & repair.

• Micronutrients are trace elements & vitamins,

which are essential for metabolic processes.

CLASSIFICATION OF FOODSCLASSIFICATION OF FOODS

• Classification by origin: - Foods of animal origin

- Foods of vegetable origin

• Classification by chemical composition: - Proteins

– Fats– Carbohydrates– Vitamins– Minerals

CLASSIFICATION BY PREDOMINANT FUNCTION

• Body building foods:• -meat, milk, poultry, fish, eggs, pulses etc

• Energy giving foods:• -cereals, sugars, fats, oils etc.

• Protective foods:• -vegetables, fruits, milk, etc

• Community Nutrition:Community Nutrition:

Identification of nutritional needs of population

groups and available resources.

• Nutritional Epidemiology:Nutritional Epidemiology:

It is the investigation of the relationship

between diet and disease.

Nutritional requirementsNutritional requirementsRecommended Dietary Allowances (RDA):

The level of nutrients considered to be adequate to meet the

nutritional needs of all healthy persons.

Knowledge of RDA is necessary to:

• Assess the nutritional adequacy of diets for

growth of infants, children and adolescents.

• Maintain health in adults of both sexes and

during pregnancy and lactation.

The adequate diet & Food The adequate diet & Food PyramidsPyramidsFood Group System:Food Group System:

• Classifies food according to similarity in

nutrient content.

• Foods placed in each group have a high

nutrient density.

Daily Food guide with Nutrient Pattern and Recommended Quantity.

Group Group Key Nutrients Key Nutrients Quantity Quantity CommentsComments

Milk and CheeseMilk and Cheese Calcium, Calcium,

ProteinProtein

Phosphorus, Phosphorus,

riboflavinriboflavin

3 cups for 3 cups for children 4 cups children 4 cups for teenagersfor teenagers

2 cups for adults2 cups for adults

Low-fat milk products Low-fat milk products have generally all the have generally all the same nutrient content, same nutrient content, however they are however they are lower in calories and lower in calories and vitamin A. vitamin A.

Meats, poultry, Meats, poultry, fish, beans fish, beans

Protein, IronProtein, Iron

Niacin, ThiaminNiacin, Thiamin

Red meat -> ZincRed meat -> Zinc

Egg yolk and liverEgg yolk and liver

-> Vitamin A-> Vitamin A

Dry beans and NutsDry beans and Nuts

-> Magnesium -> Magnesium

2 servings2 servings

Serving size: 2-3 Serving size: 2-3 ouncesounces

1 ounce of meat 1 ounce of meat

= 1 egg = 1 egg

or ½ cup cooked or ½ cup cooked beansbeans

1 ounce = 30 gm 1 ounce = 30 gm

Legumes and nuts has Legumes and nuts has a lower biological a lower biological value than meat. value than meat.

They can be combined They can be combined with animal or grain with animal or grain products to increase products to increase protein quality. protein quality. Cholesterol and Cholesterol and vitamin B12 are found vitamin B12 are found only in animal only in animal sources. sources.

Food PyramidFood Pyramid

Lessons from Food Pyramid:Lessons from Food Pyramid:

1. Maintain a healthy weight.

Studies show that the healthiest range for body weight is when the body mass index (BMI) is about 17 to 22.

2.2. Eat good fats and avoid bad fats.Eat good fats and avoid bad fats.

• Good fats are the oils found in nuts, seeds, grains and fish.

• They are high in the unsaturated fats necessary for good health.

• Good fats should contribute 30 to 45% of the total fat.

• Avoid saturated fats (animal fats and tropical oils e.g. coconut) to minimize the risk of heart disease.

• Trans-saturated fats are mainly found in margarines and commercial baked foods.

3.3. Eat whole-grain carbohydrates.Eat whole-grain carbohydrates. Why?

• whole-grainwhole-grain are more nutritious than refined are more nutritious than refined

carbohydrates carbohydrates

• Being more slowly digestedBeing more slowly digested

• Place less stress on pancreatic insulin production. Place less stress on pancreatic insulin production.

• Sources of whole grain carbohydrates include Sources of whole grain carbohydrates include

whole meal bread, whole wheat, brown rice.whole meal bread, whole wheat, brown rice.

• Avoid white bread, baked goods and pasta made Avoid white bread, baked goods and pasta made

with white flour.with white flour.

4. Avoid red meat as a protein source 4. Avoid red meat as a protein source and emphasize plant proteins.and emphasize plant proteins.

• Red meat consumption is linked to a variety Red meat consumption is linked to a variety of chronic diseases & increases the risk of of chronic diseases & increases the risk of hip fracture.hip fracture.

• Animal proteins are usually packaged with Animal proteins are usually packaged with saturated fat.saturated fat.

5. Eat plenty of vegetables and fruits.5. Eat plenty of vegetables and fruits. • Potatoes are not included as a vegetable.

• Dark green leafy vegetables, and fruit are clearly beneficial.

• A diet high in fruits and vegetables lowers blood

pressure and cholesterol and reduces the risk of cancer.

6. Take a multivitamin daily. 6. Take a multivitamin daily.

• This recommendation is insurance against any inadvertent deficiencies.

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Energy Supplying Nutrients:Energy Supplying Nutrients:

• Protein• Lipids• Carbohydrates

• Vitamins• Minerals• Water

Non-Energy Supplying Nutrients:Non-Energy Supplying Nutrients:

Main types of NutrientsMain types of Nutrients

PROTEINSPROTEINS• Proteins are complex organic nitrogenous

compounds.• They also contain sulfur and in some cases

phosphorous and iron.• Proteins are made of monomers called amino

acids.• There are about 20 different aminoacids which

are found in human body.• Of this 8-9 aa are termed “essential” as they

are not synthesized in human body and must be obtained from dietary proteins.

Protein Needs:Protein Needs:• Adults: 0.8 gm/kg body weight per dayAdults: 0.8 gm/kg body weight per day

• Excess protein is Excess protein is not usednot used to build more muscle to build more muscle

– If the body needs energy, the extra amino acids If the body needs energy, the extra amino acids are used for energyare used for energy

– If the body does not need energy, the extra amino If the body does not need energy, the extra amino acids can be converted to fat and stored.acids can be converted to fat and stored.

Sources:Sources:

• Complete proteins have all essential amino acids Complete proteins have all essential amino acids (animal sources)(animal sources)

• Incomplete proteins lack one or more essential amino Incomplete proteins lack one or more essential amino acids (plant sources)acids (plant sources)

Functions of ProteinsFunctions of Proteins

• Body buildingBody building

• Repair and maintenance of body tissuesRepair and maintenance of body tissues

• Maintenance of osmotic pressureMaintenance of osmotic pressure

• Synthesis of bioactive substances and Synthesis of bioactive substances and

other vital molecules e.g. other vital molecules e.g.

immunoglobulinsimmunoglobulins

Lipids• Lipids include cholesterol and triglycerides• Fat is necessary for health

FunctionsFunctions1. Main source of energy (9Kcal/g). 2. Spare protein.3. Adipose tissue holds the body organs and nerves

in place.4. Maintain body temperature.5. Transportation of fat soluble vitamins.

Classification• Saturated fat:Saturated fat:

– Animal foods generally are rich sources– Palm and coconut oil also are rich sources

• Monounsaturated fatMonounsaturated fat– Olives, peanuts, and canola oil are rich sources

• Polyunsaturated fatPolyunsaturated fat– Corn, sunflower, cotton seed, and nut oils are rich sources

• Hydrogenated fatHydrogenated fat

Hydrogenated fat• Hydrogenation process hardens liquid oils into more

solid margarine.

– It makes unsaturated fat in oil more saturated

– Also it produces an unhealthy type of fat called

“trans fatty acid”“trans fatty acid”

• Saturated fat and trans fatty acids may be harmful to

health

• Baked products and fried foods are often made with

hydrogenated fats

CholesterolCholesterol

• Cholesterol is necessary for cell membranes and the Cholesterol is necessary for cell membranes and the

production of vitamin D, bile, and certain hormonesproduction of vitamin D, bile, and certain hormones

• It is found It is found onlyonly in in animalanimal foods foods

• High blood cholesterol levels are associated with High blood cholesterol levels are associated with

increased risk of increased risk of heartheart disease disease

Fats yield fatty acids and Fats yield fatty acids and glycerol on hydrolysisglycerol on hydrolysis

• Fatty acid content of different fats ( in per cent)• Saturated Monounsaturated

Polyunsaturated

• Fats fatty acids fatty acids fatty acids

• Coconut oil 92 6 2• Palm oil 46 44 10• Cotton seed oil 25 25 50• Groundnut oil 19 50 31• Sunflower oil 8 27 65 • Corn oil 8 27 65• Soya bean oil 14 24 62• Butter 60 37 3

Fat requirementsFat requirements

• The WHO Expert committee on Prevention of The WHO Expert committee on Prevention of

Coronary Heart Disease has recommended Coronary Heart Disease has recommended

only only 20 to 3020 to 30 per cent of total dietary energy per cent of total dietary energy

to be provided by fats. (<30%)to be provided by fats. (<30%)

• At least 50 per cent of fat intake should At least 50 per cent of fat intake should

consist of consist of vegetablevegetable oils rich in essential fatty oils rich in essential fatty

acids. acids.

CarbohydratesCarbohydratesFunctions:Functions:

1. Carbohydrate is the main source of energy, providing 4 Kcals per one gram

2. Carbohydrate is essential for the synthesis of certain non-essential amino acids.

3. Necessary for normal fat metabolism.

4. Necessary for integrity of nerve cells.

5. Lactose allow growth of beneficial bacteria in the intestine.

6. Important for normal elimination (excretion); fibers

Recommended carbohydrate intake is 55% to 65% of calories, primarily from starchy foods

Classification of Classification of CarbohydratesCarbohydrates

1.1. Monosaccharides: glucose &fractoseMonosaccharides: glucose &fractose

2.2. Disaccharides: Sucrose (G + F)Disaccharides: Sucrose (G + F)

3.3. Oligosaccharides (3-10).Oligosaccharides (3-10).

4.4. Polysaccharides (11-1000)Polysaccharides (11-1000)

a-Indigestable e.g. cellulosea-Indigestable e.g. cellulose

b-partially digestable e.g.raffinoseb-partially digestable e.g.raffinose

c-Digestable e.g. starchc-Digestable e.g. starch

The inability of the body to metabolize The inability of the body to metabolize carbohydrates properly =DMcarbohydrates properly =DM

FiberFiber• Indigestible plant material e.g. cellulose

• Dietary fiber is mainly non-starch polysaccharide

• It is found in vegetables, fruits and grains.

• SolubleSoluble fiber swells or dissolves in water

– Rich sources include apples, bananas, citrus fruits, carrots

• Importance:

– Reduces cholesterol absorption

– Slows absorption of glucose

FiberFiber• InsolubleInsoluble fiber fiber remains unchanged in water

– Rich food sources include brown rice, wheat bran,

and whole grain products

• Importance:• High fiber diet reduces the risk of heart disease,

diabetes type II, diverticulosis, hemorrhoids, constipation, and possibly colorectal cancer

* Refined foods lose fiber-rich parts during processing

Non-Energy Supplying Nutrients

• VitaminsVitamins

• MineralsMinerals

• WaterWater

Vitamins

• Regulate growth,

• maintain tissues, and

• help carbohydrates, proteins, and fats release

energy

• Provide no calories (energy)

• Needed in very small amounts

Classes of VitaminsClasses of Vitamins• Water SolubleWater Soluble: 8 different B vitamins and : 8 different B vitamins and

vitamin Cvitamin C

• Fat SolubleFat Soluble: Vitamins A, D, E, and K: Vitamins A, D, E, and K

• Most healthy people do not need supplements; Most healthy people do not need supplements;

vitamins can be obtained by eating a variety of vitamins can be obtained by eating a variety of

foodsfoods

– Supplementation can increase the risk of Supplementation can increase the risk of

consuming toxic high levels consuming toxic high levels

Vitamin AVitamin A

• «Vitamin A» covers both:

– a pre-formed vitamin, retinol, and

– a pro-vitamin, beta carotene, which is converted to

retinol in the intestinal mucosa.

Sources:

– Retinol in liver, code liver oil & eggs (animal sources)

– Beta carotene: Coloured plants e.g. carrot, mango, apricot,

pumpkin,….. (plant sources)

Fat soluble vitamins

VITAMIN ASources: • liver • milk • eggs • spinach • carrots • tomatoes • butter

Functions of Vitamin AFunctions of Vitamin A

• It is essential for normal vision. It is essential for normal vision.

• It is necessary for maintaining the integrity and the It is necessary for maintaining the integrity and the

normal functioning of glandular and epithelial tissue normal functioning of glandular and epithelial tissue

which lines intestinal, respiratory and urinary tracts as which lines intestinal, respiratory and urinary tracts as

well as the skin and eyes. well as the skin and eyes.

• It supports growth, especially skeletal growthIt supports growth, especially skeletal growth

• It may protect against some epithelial cancers such as It may protect against some epithelial cancers such as

bronchial cancers.bronchial cancers.

Vitamin DVitamin D

• The nutritionally important forms of

Vitamin D in man are:

– Calciferol (Vitamin D2) and

– Cholecalciferol (Vitamin D3)

• Sources: Present in egg yolk + natural

(ultraviolet rays in sunlight).

VITAMIN D• contains in:

• liver

• caviar

• butter

Functions of vitamin DFunctions of vitamin D

• Intestine: Promotes intestinal absorption of

calcium and phosphorus

• Bone: Stimulates normal mineralization,

Enhances bone reabsorption, Affects

collagen maturation

• Kidney: Increases tubular reabsorption of

phosphate

Deficiency of vitamin DDeficiency of vitamin D

Deficiency of vitamin D leads to:Deficiency of vitamin D leads to:

• Rickets in children

• Osteomalacia in adults

Vitamin E

• Antioxidant- Protects RBCs from haemolysis.

• Present in wheat germ and green leafy vegetables

Vitamin K

• Important for blood coagulation

• Present in leaves of plants + natural (flora).

• Deficiency causes haemorrhagic manifestations.

VITAMIN E contains in:

• liver

• corn

• eggs

• vegetable oils

Water soluble vitamins

Thiamine (B1)

• Function: essential for the utilization of

carbohydrates.

• Present in brewer yeast, beans and legumes.

• Deficiency: Beri-beri

Deficiency of thiamineDeficiency of thiamine

• Beriberi may occur in three main forms:

– peripheral neuritis,

– cardiac beriberi,

– infantile beriberi, signs of peripheral

neuropathy.

The Water-Soluble Vitamins

Overview of Water-Soluble Vitamins

• Dissolve in water

• Generally readily excreted

• Subject to cooking losses

• Function as a coenzyme

• Participate in energy metabolism

• 50-90% of B vitamins are absorbed

• Marginal deficiency more common

Enrichment Act of 1941 and 1998

• Many nutrients lost through milling process of grains

• Grain/cereal products are enriched

• Thiamin, riboflavin, niacin, folate, iron

• Whole grains contain original nutrients

• Enriched grains still deficient in B-6, magnesium and zinc

Thiamin

• Contains sulfur and nitrogen group

• Destroyed by alkaline and heat

• Coenzyme: Thiamin pyrophosphate (TPP)

Food Sources of Thiamin

• Wide variety of food

• White bread, pork, hot dogs, luncheon meat, cold cereal

• Enriched grains/ whole grains

• Thiaminase found in raw fish

Absorption, Transport, Metabolism of Thiamin

• Absorbed in the jejunum by a carrier-mediated system

• Transported by RBC in the blood

• Excess quickly excreted in the urine

Function of Thiamin (Fig. 10-2)

Coenzyme: Thiamin Pyrophosphate (TPP)

• Synthesis of neurotransmitter

• Convert pyruvate to acetyl-CoA CoA NAD+ NADH + H+

Glucose Pyruvate Acetyl-CoA Citric

CO2 Acid Cycle

RDA For Thiamin

• 1.1 mg/day for women

• 1.2 mg/day for men

• Most exceed RDA in diet

• Surplus is rapidly lost in urine; non toxic

Who is at Risk For Deficiency?

• Poor

• Alcoholics

• Elderly

• Diet consisting of highly processed foods

Deficiency of Thiamin

• Occurs where rice is the only staple

• Dry beriberi– Weakness, nerve degeneration, irritability,

poor arm/leg coordination, loss of nerve transmission

• Wet beriberi– Edema, enlarge heart, heart failure

Riboflavin

• Coenzymes:– Flavin mononucleotide (FMN)– Flavin adenine dinucleotide (FAD)

• Oxidation-reduction reactions

• Electron transport chain

• Citric Acid Cycle

• Catabolism of fatty acids

Food Sources of Riboflavin

• Milk/products

• Enriched grains

• Liver

• Oyster

• Brewer’s yeast

• Sensitive to uv radiation (sunlight)

• Stored in paper, opaque plastic containers

Absorption, Transport, & Metabolism of Riboflavin

• HCL in the stomach release riboflavin from its bound forms

• Absorption– Active or facilitated transport during low to

moderate intake– Passive absorption during high intake– Increase with intake

• Transported by a protein carrier in the blood

Functions of Riboflavin

• Accepts electrons Electron Transport Chain

FAD FADH2

Succinate Fumarate Citric Acid Cycle

• Participates in beta oxidation• FMN shuttles hydrogen ions and electrons to

into the electron transport chain

RDA for Riboflavin

• 1.1 mg/day for women

• 1.3 mg/day for men

• Average intake is above RDA

• Toxicity not documented

Who is at Risk For Deficiency?

– Rare– Low milk/dairy intake– Alcoholics– Long term phenobarbital use

Deficiency of Riboflavin

• Ariboflavinosis– Glossitis, cheilosis, seborrheic dermatitis,

stomatitis, eye disorder, throat disorder, nervous system disorder

• Occurs within 2 months

• Usually in combination with other deficiencies

Glossitis

Niacin

• Nicotinic acid (niacin) & nicotinamide (niacinamide)

• Coenzyme– Nicotinamide adenine dinucleotide (NAD)– Nicotinamide adenine dinucleotide phosphate

(NADP)• Oxidation-reduction reaction• Metabolic reactions

Food Sources of Niacin

• Mushrooms

• Enriched grains

• Beef, chicken, turkey, fish

• Heat stable; little cooking loss

Absorption, Transport and Storage of Niacin

• Readily absorbed from the stomach and small intestine

• Absorption: active transport and passive diffusion

• Transported from the liver to all of the tissues where it is converted to the coenzymes

Functions of Niacin• NAD and NADP participates in 200+ reactions in the

body2 NAD+ 2NADH + H+

Glucose Pyruvate

NAD+ NADH + H+

Pyruvate Lactate

NAD+ NADH + H+

Isocitrate Alpha-ketogluterate NAD+ NADH + H+ Alpha-ketogluterate Succinyl CoA NAD+ NADH + H+

Malate Oxaloacetate

• Electron transport chain

Citric Acid Cycle

RDA for Niacin

• 14 NE/day for women

• 16 NE/day for men

Deficiency of Niacin• Pellagra

– 3 Ds – Occurs in 50-60 days– Decrease appetite & weight

• Prevented with an adequate protein diet• Enrichment Act of 1941• Only dietary deficiency disease to reach epidemic

proportions in the U.S.• Who is at risk?

– (Untreated) corn as main staple, poor diet, Hartnup disease, alcoholics

Dermatitis of Pellegra

Niacin as a Medicine

• 75-100 x RDA can lower LDL and TG and increase HDL

• Slow/ reverse progression of atheroscelerosis with diet and exercise

• Toxicity effects– Flushing of skin, itching, nausea, liver

damage

Pantothenic Acid

• Part of Coenzyme-A• Essential for metabolism of CHO, fat,

protein

Glucose

Fatty acids Acetyl-CoA Amino Acids

Alcohol

Food Sources of Pantothenic acid

• Meat• Milk• Mushroom• Liver• Peanut• Adequate Intake = 5 mg/day• Average intake meets AI

Deficiency of Pantothenic Acid

• Rare• Burning foot syndrome, listlessness,

fatigue, headache, sleep disturbance, nausea, abdominal distress

• Alcoholics at risk• Usually in combination with other

deficiencies

Biotin

• Free and bound form

• Biocytin (protein bound form)

• Biotinidase in small intestine

• Metabolism of CHO, fat, protein (C skeleton)

• DNA synthesis

Food Sources of Biotin

• Cauliflower, yolk, liver, peanuts, cheese• Intestinal synthesis of biotin• Biotin content only available for a small number

of foods• Unsure as to bioavailablity of synthesized biotin• We excrete more than we consume• Avidin inhibits absorption

– > a dozen of raw eggs a day to cause this effect

Functions of Biotin

• Assists in the addition of CO2 to substances• Carboxylation of acetyl-CoA to form malonyl-

CoA for the elongation of a fatty acid chain• Addition of CO2 to pyruvate to yield

oxaloacetate• Breaks down leucine• Allows 3 essential amino acids to be oxidized

for energy

Biotin Needs

• Adequate Intake is 30 ug/day for adults

• This may overestimate the amount needed for adults

• No Upper Limit for biotin

Who is at Risk For Deficiency?

• Rare• High intake of raw egg white diet• Alcoholics• Biotinidase deficiency• Anticonvulsant drug use• Signs & symptoms: skin rash, hair loss,

convulsion, neurological disorders, impaired growth in children

Vitamin B-6: Pyridoxal, Pyridoxine, Pyridoxamine

• Main coenzyme form: pyridoxal phosphate (PLP)

• Activate enzymes needed for metabolism of CHO, fat , protein

• Transamination

• Synthesis of hemoglobin and oxygen binding and white blood cells

• Synthesis of neurotransmitters

Food Sources of Vitamin B-6

• Meat, fish, poultry

• Whole grains (not enriched back)

• Banana

• Spinach

• Avocado

• Potato

• Heat and alkaline sensitive

Absorption and Metabolism of Vitamin B-6

• Absorbed passively

• All three forms of B-6 are phosphorylated in the liver

• Binds to albumin for transport in the blood

• B-6 is stored in the liver and muscle tissue

• Excess is excreted in urine

Functions of Vitamin B-6• Participates in 100+ enzymatic reactions• Decarboxylation of amino acid (decarboxylase)• Transamination reaction (transaminase)• Structural rearrangement of amino acids

(racemase)• RBC synthesis• CHO metabolism• Lipid metabolism• Neurotransmitter Synthesis• Conversion of tryptophan to niacin

RDA for Vitamin B-6

• 1.3 mg/day for adults

• 1.7 mg/day for men over 50

• 1.5 mg/day for women over 50

• Daily Value set at 2 mg

• Average intake is more than the RDA

Deficiency of Vitamin B-6• Microcytic hypochromic anemia• Seborrheic dermatitis• Convulsion, depression, confusion• Reduce immune response• Peripheral nerve damage• Who is at risk?

– Elderly– Alcoholics

• Alcohol decreases absorption• Destroy the coenzyme form

B-6 As A Medicine?

• PMS– B-6 to increase the level of serotonin– Improve depression– Not a reliable treatment

• Carpal tunnel syndrome

• Toxicity potential

• Can lead to irreversible nerve damage with > 200 mg/day

Folate (Folic acid, Folacin)

• Consists of pteridine group, para-aminobenzoic acid (PABA), and glutamic acid

• Coenzyme form: tetrahydorfolic acid (THFA)

Food Sources of Folate

• Liver

• Fortified breakfast cereals

• Grains, legumes

• Foliage vegetables

• Susceptible to heat, oxidation, ultraviolet light

Absorption, Metabolism of Folate

• Absorbed in the monoglutamate form with help of folate conjugase

• Actively absorbed during low to moderate intake• Passively absorbed during high intake• Delivered to the liver where it is changed back

to the polyglutamate form• Mostly stored in the liver• Excreted in the urine and bile (enterohepatic

circulation)

Functions of Folate

• DNA synthesis– Transfer of single carbon units– Synthesis of adenine and guanine– Anticancer drug methotrexate

• Homocysteine metabolism

• Neurotransmitter formation

RDA for Folate

• 400 ug/day for adults

• Daily Value is set at 400 ug

Deficiency of Folate

• Similar signs and symptoms of vitamin B-12 deficiency

• Pregnant women

• Alcoholics– Interferes with the enterohepatic circulation of

bile/folate

Megaloblastic Anemia

Neural Tube Defects

• Spina bifida• Anencephaly• Importance of folate

before and during pregnancy

Toxicity of Folate

• Epilepsy

• Skin, respiratory disorder

• FDA limits nonprescription supplements to 400 ug per tablet for non-pregnant adults

• OTC Prenatal supplement contains 800 ug

• Excess can mask vitamin B-12 deficiency

Vitamin B-12

• Cyanocobalamin. methlcobalamin,

5-deoxyadenosylcobalamin

• Contains cobalt

• Folate metabolism

• Maintenance of the myelin sheaths

• Rearrange 3-carbon chain fatty acids so can enter the Citric Acid Cycle

Food Sources of Vitamin B-12

• Synthesized by bacteria, fungi and algae• (Stored primarily in the liver)• Animal products• Organ meat• Seafood• Eggs• Hot dogs• Milk

Absorption of Vitamin B-12

Therapy for Ineffective Absorption

• Many factors can disrupt this process

• Monthly injections of vitamin B-12

• Vitamin B-12 nasal gel

• Megadoses of vitamin B-12 to allow for passive diffusion

Functions of Vitamin B-12

• Helps convert methylmalonyl CoA to succinyl CoA (citric acid cycle)

• RBC formation

• Nerve functions– Maintains myelin sheath

• Megalobalstic anemia

Vitamin B-12 and Homocysteine(Fig. 10-11)

RDA for Vitamin B-12

• 2.4 ug/ day for adults and elderly adults

• Average intake exceeds RDA

• B-12 stored in the liver

• Non-toxic

Who is at Risk For Deficiency?

• Vegans

• Breastfed infants of vegan moms

• Elderly

• Individuals with AIDS or HIV

Deficiency of Vitamin B-12

• Pernicious anemia– Never degeneration, weakness– Tingling/numbness in the extremities (parasthesia)– Paralysis and death– Looks like folate deficiency

• Usually due to decreased absorption ability• Achlorhydria especially in elderly• Injection of B-12 needed• Takes ~20 years on a deficient diet to see

nerve destruction

Vitamin C

• Ascorbic acid (reduced form), dehydroascorbic acid (oxidized form)

• Synthesized by most animals (not by human)

• Absorbed by a specific energy dependant transport system

• Passive transport if intake is high• Decrease absorption with high intakes• Excess excreted

Food Sources of Vitamin C

• Citrus fruits• Potatoes• Green peppers• Cauliflower• Broccoli• Strawberries• Romaine lettuce• Spinach

• Easily lost through cooking

• Sensitive to heat• Sensitive to iron,

copper, oxygen

Functions of Vitamin C

• Reducing agent (antioxidant)• Iron absorption• Synthesis of carnitine, tryptophan to

serotonin, thyroxine, cortiscosteroids, aldosterone, cholesterol to bile acids

• Immune functions• Cancer prevention?• Collagen synthesis

Collagen Synthesis (Fig. 10-12)

Antioxidant

• Can donate and accept hydrogen atoms readily

• Water-soluble intracellular and extracellular antioxidant

• Must be constantly enzymatically regenerated

• Needs are higher for smokers

RDA for Vitamin C

• 90 mg/day for male adults• 75 mg/day for female adults• +35 mg/day for smokers• Average intake ~72 mg/day• Fairly nontoxic (at <1 gm)• Upper Level is 2 g/day• Warning to people with hemochromatosis,

oxalate kidney stones

Deficiency of Vitamin C• Scurvy

– Deficient for 20-40 days – Fatigue, pinpoint hemorrhages– Bleeding gums and joints. Hemorrhages– Associated with poverty

• Rebound scurvy– immediate halt to excess vitamin C supplements

• Who is at risk?– Infants, elderly men – Alcoholics, smokers