Nutrition Science Midterm 2

The Central Dogma

• A theory that states information in an organism that decides an organism, and describes everything that it can do, is encoded in the DNA

• DNA is then copied into RNA, which is very similar, it has exactly the same sequences as DNA, but can easily be changed

• From the information in the RNA, you can make protein by reading the sequences of bases in the RNA 3 at a time & 3 code for one amino acid

The Central Dogma (cont.)

• Information from nucleic acids cannot be back-engineered

• Nucleic acids → protein

Protein Synthesis: Transcription & Translation

• In the nucleus the blueprint or code, for the protein is copied or transcribed from the DNA gene into a molecule of messenger RNA

• The mRNA takes the genetic information from the nucleus to structures called ribosomes in the cytosol, where proteins are made

• In the cytosol, transfer RNA reads the genetic code & delivers the needed amino acids to the ribosome to form a polypeptide chain

Amin Acid Pool Allows for Amino Acid Availability

Amino Acid Pool

• an accumulation of amino acids in the liver & blood that adjusts to meet the body’s need for protein & amino acids

Limiting amino acid

• Our bodies use amino acids in a specific ratio to each other, so if a person doesn’t get enough of one of them to match w/ the rest, the rest can only be used at a level to balance w/ that low one

• The amino acid that is deficient in the diet is the limiting amino

Metabolism, Physiology, Behavior

Metabolism ←> Physiology ←> Behavior

Pathways of amino acid metabolism

Amino Acids: Transamination

• When a nonessential amino acid is not available from the diet, it can be made in the body by the process of transamination

Deamination & Synthesis of a Nonessential Amino Acid

• The deamination of an amino acid produces ammonia & a keto acid (removal of an amino group)

• Given a source of ammonia, the body can make nonessential amino acids from keto acids

Energy Production from Protein

• The amino group is removed by deamination

• Deamination of some amino acids produces 3-carbon molecules that can be used to synthesize glucose, via gluconeogenesis

• Deamination of some amino acids results in 2-carbon molecules that form acetyl-CoA, which can enter the citric acid cycle or be used to synthesize fatty acids

• Deamination of some amino acids forms molecules that are intermediates in the citric acid cycle

• High-energy electrons from the breakdown of amino acids are transferred to the electron transport chain where the energy is trapped & used to produce ATP & water

Urea Synthesis

• Amino acids are deaminated before they can be metabolized to produce ATP or used to synthesize glucose or fat

• The amino group forms toxic ammonia

• Ammonia is converted into urea in the liver

• Urea can safely travel in the blood & is filtered out of the blood by the kidney & eliminated from the body in the urine

Nitrogen Balance

B = I - (U + F +S)

• B is nitrogen balance

• I is nitrogen intake

• U is urinary nitrogen

• F is fecal nitrogen

• S loss of nitrogen through the skin

Proteins in the Diet

• Recommended protein intake:

  • Adult RDA = .8g/kilogram body weight

  • Infant RDA = 1.5 g/kilogram body weight

  • Elderly = 1 to 1.2 g/kg

Positive Nitrogen Balance

Situations when positive nitrogen balance occur:

• growth

• pregnancy

• recovery stage after illness/injury

• athletic training resulting in increased lean body mass

• increase secretion of certain hormones such as insulin, growth hormone, & testosterone

Nitrogen Equilibrium

Situations when nitrogen equilibrium occurs:

• healthy adult meeting protein & energy needs

Negative Nitrogen Balance

Situations when negative nitrogen balance occur:

• inadequate intake of protein

• inadequate energy intake

• severe conditions such as fevers, burns, & infections

• severe bad rest (for several days)

• deficiency of essential amino acids

• increased secretion of certain hormones such as thyroid hormone & cortisol

Examples of Protein (Nitrogen) Balance

• a pregnant women adds protein so she has a positive nitrogen balance

• a healthy person who is neither gaining nor losing nitrogen is in nitrogen equilibrium

• a person who is severely ill & losing protein has a negative nitrogen balance

Nitrogen Approximation

• Nitrogen makes up approximately 16% of the weight of an amino acid

• Nitrogen intake multiplied by 6.25 provides an estimate of protein intake

• A crude estimate of the % protein content of food = N x 100/6 = N x 6.25

Apparent digestibility

[N (eaten) - N (fecal) ] / N (eaten) x 100

Protein Efficiency Ratio

• PER = live weight gain/crude protein intake

• if a particular diet doesn’t support growth, then a PER of 0 will be recorded

Factors that affect protein quality:

• digestibility

• amino acid content

• toxins (trypsin inhibitor)

• form of amino acids

When measuring quality of a protein need to consider calorie intake:

• Isocaloric diets - Test diet & control diets have the same caloric density

• Pair feeding - The caloric intake between subjects on the control & those subjects on the test diet are equal

Protein Complementation

• Combining plant protein sources to achieve a better amino acid balance than each would have along

• Legumes: peas, beans, lentils, peanuts, alfalfa

• Grain: wheat, rice, corn, oats, rye

Proteins that may harm certain individuals: Phenylketonuria

• PKU is an inherited condition attributed to a defective gene

• Aspartame, a sugar substitute, contains phenylalanine

Protein Deficiency

• Protein-energy malnutrition (PEM) is used to refer to the continuum of protein deficiency conditions, ranging from mostly protein deficiency called

  • 1) kwashiorkor

  • 2) marasmus

Kwashiorkor

• Severe protein deficit, often accompanied by infections or other diseases

• Characteristics:

  • Edema (swelling)

  • Mild to moderate weight loss

  • Maintenance of some muscle & subcutaneous fat

  • Growth impairment

  • Rapid onset

  • Fatty liver

Marasmus

• Severe energy & protein deficit

• Characteristics:

  • Severe weight loss

  • Wasting of muscle & body fat (skin & bones appearance)

  • Severe growth impairment

  • Develops gradually

Pros & Cons of Vegetarian Eating

• Types of vegetarian diets

  • semi-vegetarian

  • lacto-ovo vegetarian

  • vegan

• Health benefits vs. health risks

  • less fat, saturated fat, & cholesterol

  • restrictive diets may lack nutrients

  • careful planning needed for children, pregnant women

Nutrients Supplied by Plant & Animal Foods

• Animal products provide sources of:

  • Protein

  • B vitamins

  • Minerals such as iron, zinc, & calcium

• However, animal products are low in fiber & can be high in fat

• Plant sources of protein are also a good source of:

  • B vitamins

  • Iron

  • Zinc

  • Fiver

  • Calcium

    • But in less absorbable forms

Protein Quality of Various Food Proteins

Food Protein Allergies

• Food proteins (allergens) cause an immune response, creating an allergic reaction

  • IgE most commonly produced (antibodies produced by the immune system)

  • anaphylaxis (a severe, life-threatening allergic reaction that can occur rapidly after exposure to an allergen)

• 8 foods account for 90% of all food allergies

  • peanuts, tree nuts, milk, eggs, fish, shellfish, soy, & wheat

Too Much Protein

• heart disease

• obesity

• cancer

• osteoporosis (a bone disease that weakens bones, making them more likely to break)

• protein & amino acid supplements

  • generally not needed w/ risks unknown

• kidney stones

• hydration & kidney function

Protein Excess

• Hydration & kidney function

  • When protein intake increases above the amount needed, so does the production of protein breakdown products such as urea, which must be eliminated from the body by the kidneys. To do this, more water must be excreted in the urine, increasing water losses

• Kidney Stones

  • The increase in urinary calcium excretion associated w/ high-protein diets has led to speculation that a high protein intake may increase the risk of kidney stones

• Heart Disease & Cancer

  • High-protein diets is related more to the dietary components that accompany animal versus plant proteins. Typically, high protein diets are also high in animal products, this dietary pattern is high in saturated fat & cholesterol & low in fiber

Celiac Disease

• wheat or gluten intolerance

• found in wheat, rye, & barley

Photosynthesis

Carbohydrates

• Macronutrient

  • 4 kcal/g

• Carbon, oxygen, hydrogen

  • Carbon-hydrate: C +H20

  • CHO

• Glucose: C6H1206

Carbohydrates Functions

• provides energy

• spares protein

• provides sweetness

• provides fiber

• enhances functions of many proteins

Carbohydrate Types

• Simple

  • Monosaccharides (e.g glucose, fructose)

  • Disaccharides (e.g sucrose “sugar”: glucose + fructose)

• Complex (3 or more monosaccharides)

  • oligosaccharides

  • polysaccharides (starch, fiber, glycogen)

Monosaccharides

• Glucose

  • most abundant sugar molecule in our diet; good energy source

• Fructose

  • sweetest natural sugar; found in fruit, high-fructose corn syrup

• Galactose

  • does not occur alone in foods; binds w/ glucose to form lactose

Lactose Intolerance

• not enough lactase in the SI to digest lactose

• symptoms: diarrhea, bloating, intestinal gas

Oligosaccharides

• 3-10 monosaccharides

• Indigestible molecular bonds

• Colonic bacteria digest = gas, short chain fatty acids

Insoluble & Soluble Fiber

1) Insoluble fiber

• part of cell wall

• don’t dissolve in water

• contributes bulk to stool

• examples: cellulose, hemicellulose

• good sources: whole grains, fruits, veggies

2) Soluble Fiber

• dissolve in water, are viscous & gel-forming

• bacteria metabolize-like oligosaccharides

• examples: gums, pectin

• good sources: fruits, berries, oats

Polysaccharides

• starch: storage form of glucose in plants; food sources include grains, legumes, & tubers

  • amylose

  • amylopectin

• glycogen: storage form of glucose in animals; stored in liver & muscles

• fiber: forms the support structures of leaves, stems, & plants

Fiber: Health Benefits

• High fiber diets may:

  • promote weight loss

  • promote regular bowel movements

  • prevent constipation

  • prevent hemorrhoids & diverticulitis

  • lower the risk of colon cancer

Soluble Fiber: Health Benefits

• lowers cholesterol

  • soluble fiber binds w/ bile

  • decreases (re)absorption of bile acids

  • increases hepatic cholesterol → bile acids

  • increases LDL uptake by liver

• delays rise in blood glucose

  • fiber in food ‘traps’ nutrients

  • delays nutrient absorption

  • stabilizes blood sugar levels

Enterohepatic Circulation of Bile

Whole Grains versus Refined Grains

• whole or unrefined grains contain:

  • bran layers: good source of fiber & vitamins

  • germ: good source of vegetable oils & vitamin E

  • endosperm: contains starch & some protein

Fates of Glucose

• monosaccharides enter capillaries, travel to liver

• in liver cells, fructose & galactose → glucose

• Glucose:

  • used for energy in liver

  • passed into the blood for other cells to use for energy

  • store in liver & muscles as glycogen

  • if consumed in excess energy needs → synthesize fatty acids

Starch breakdown in small intestine

Pancreatic Enzymes

• amylase: breaks down carbohydrates (starch) into sugars which are more easily absorbed by the body

  • also found in saliva

  • a shortage may cause: diarrhea due to the effects of undigested starch in the colon

Digestion & absorption in the small intestine

Glucose Catabolism: Glycolysis

• glyco = sugar, lysis = breakdown

• the metabolic pathway that converts glucose into pyruvate

• the free energy released in this process is used to form the high-energy compounds ATP

• doesn’t require oxygen, it is a way to produce ATP anaerobically (w/o oxygen) and is known as anaerobic cellular respiration

Creating ATP through Cellular Respiration

• Glycolysis → citric acid cycle → electron transport chain

Glycogen Levels

• Glycogen

  • storage form of glucose

  • liver can store 100g glycogen (400 kcal)

    • used to maintain blood glucose

  • muscles store 350 g (1400 kcal muscle needs)

Gluconeogenesis

• making glucose from non-glucose substrates

• glucagon initiates this when CHO intake is low

Overview: Glucose & Glycogen

Exocrine & Endocrine Pancreas and Starch breakdown

Blood Glucose Regulation

• insulin: decrease in blood glucose

• glucagon: increase blood glucose

Diabetes mellitus (diabetes)

• a group of metabolic disorders characterized by a high level of blood sugar over a prolonged period of time

• it results from the inability to regulate blood sugar

Blood glucose levels in diabetes

Type 1 Diabetes

• Juvenile-onset diabetes

• Autoimmune disease affecting beta cells of pancreas

• insulin injections

• accounts for 5-10% of total diabetes cases in the US

• symptoms: frequent urination, unusual thirst, extreme hunger, unusual weight loss, extreme fatigue, irritability, ketone bodies

Type 2 Diabetes

• was called adult-onset diabetes or NIDDM

• 95% of cases in US are T2D

• resistance or decrease response to insulin

• diet, exercise, oral meds can help control

Types 2 Diabetes Risk Factors

• > 45 years old

• family history

• overweight/obesity (BMI >25)

• central weight

• sedentary lifestyle

• decrease in HDL and/or increase TG

• some racial/ethnic groups (Indigenous Americans, African American, Latin American)

Hypoglycemia

• low blood sugar (glucose)

• causes shakiness, sweating, anxiety

• reactive hypoglycemia: pancreas secretes too much insulin after a high-carbohydrate meal

Glycemic Response

• a food’s potential to raise blood glucose levels

• increase in glycemic index (GI) → increase in blood glucose levels

• Influenced by the amount & type of CHO & protein, fat, and fiber content

• Glycemic load = GI x CHO grams in food

The Glycemic index

• 1) High (GI 70+)

• 2) Medium (GI 55-59)

• 3) Low (GI 54 or less)

Gluconeogenesis

• making glucose from non-glucose substrates

• glucagon initiates this when CHO intake is low

Carbohydrates Are Needed to Break Down Fate to carbon dioxide and water

Functions of Lipids (Fat)

• provide energy at rest, fasting & during moderate-intensity exercise, prolonged exercise

• typical American diet contains about 33%

• energy storage (triglyceride in adipose tissue)

• padding (protection) & insulation

• components of cell membranes

• many compounds are synthesized from lipids

• absorption & transport fat-soluble vitamins

• satiety, flavor, taste, & aroma of foods

Types of Lipid Molecules

• Free Fatty Acids

• Triglycerides (TG) (Fats)

• Phospholipids

• Sterols

Fatty acids: Chain length

• short chain FA: fewer than 6 carbons butyric acid (butter)

• medium chain FA: 6-12 carbons lauric acid (coconut oil)

• long chain FA: 14 or more linoleic (safflower oil)

Fatty Acid Structures

• saturated fatty acids

• unsaturated fatty acids

  • polyunsaturated

    • omega-6

    • omega-3

  • monounsaturated

Triglycerides

• three fatty acid molecules

  • fatty acids are long chains of carbon atoms bound to each other as well as to hydrogen atoms

• one glycerol molecule

  • glycerol is a 3-carbon alcohol that is the backbone of a triglyceride

• Condensation reaction (TG synthesis)

• Hydrolysis reaction (lipase)

• 3 fatty acids + glycerol → triglyceride

• are the major form of lipid in the food & in the body

Types of Fatty Acids -Effects on Cholesterol

• saturated (SFA): not food

  • raised cholesterol

  • coconut oil, palm kernel oil, butter, cream, cheese, beef fat, whole milk

• monounsaturated (MUFA): neutral

  • olive oil, canola oil, peanut oil, cashew nuts

• polyunsaturated (PUFA): good

  • veggie oils, seeds, almonds, walnuts, soy, fish

• * shape impacts stacking ability & fluidity

Essential Fatty Acids

• are those polyunsaturated fatty acids (PUFA) that must be provided by foods because these cannot be synthesized in the body yet are necessary for health

• two families of EFA: omega-3 and omega-6

Essential fatty acid deficiency

• are important for growth, skin integrity, fertility, & the structure and function of cell membranes

• if adequate amounts of essential fatty acids aren’t consumed, a deficiency can result

• symptoms include: dry, scaly skin, live abnormalities, poor wound healing, growth failure in infants, & impaired hearing and vision

Sources of Essential Fatty Acids

• omega 6 fatty acids (main dietary source is linoleic)

  • most vegetable oils, nut & seed oils

• omega 3 fatty acids (main dietary source is alpha-linolenic)

  • soy oil, flaxseed, leafy green vegs

  • fish have longer chain omega 3: EPA, DHA (can also be produced from dietary alpha-linoleic)

  • associated w/ reduced heart disease

Omega 6: Omega 3 Requirements

• omega 6: omega 3.

  • 10:1

Essential Fatty Acids & Eicosanoid synthesis

• the ratio of dietary omega-6 to omega-3 essential fatty acids affects the balance of these fatty acids in the tissues & thus the ratio of the types of eicosanoids made from them

Trans Fatty Acids

• can be created during food processing by hydrogenation

• hydrogenation causes some double bonds to become saturated

• hydrogenated facts can be found in margarines, vegetable shortening & shelf-stable baked goods

• trans fatty acids have to be shown to raise blood cholesterol levels & increase the risk of heart disease

Trans Fatty Acids Structure

Phospholipids

• 2 fatty acids

• glycerol

• phosphorous -containing molecule

• properties: hydrophobic & hydrophilic ends

• Function:

  • helps w/ fat absorption (emulsifier)

    • lecithin + bile salts + electrolytes = bile

  • help transport dietary facts in circulation

  • part of the cell membrane

  • in food: emulsifier (mayonnaise, salad dressing)

• Liver makes phospholipids so not essential

• Foods: animal cell membranes, egg yolks

Emulsification

Sterols

• 4 carbon rings

• found in food & made in body

• cholesterol is most common dietary sterol -only found in animals

• high cholesterol increases CHD risk

• plant sterols can reduce CHD risk

Cholesterol (a sterol)

• functions:

  • bile salt precursor

  • cell membrane structure

  • hormones (glucocorticoids, estrogen, testosterone)

  • vitamin D

• Sources: produced by animals

  • animal products

• non-essential in the diet

• health issue: raises LDL-C cholesterol

• General goal <300 mg/day in the diet

• 3 oz meat ~ 100 mg

Lipid digestion & absorption (a)

Lipids Absorption & Transport

• FAs don’t mix well w/ water

• bile = emulsifier

• micelles formed

  • transport lipid digestion products into enterocytes

Lipase Action

• mouth: not much, some in infants

• stomach: gastric lipase… not much

• small intestine:

  • CCK: stimulates gall bladder to release bile & pancreatic lipase

  • Lipases break TG into monoacylgyceride & 2 free fatty acids

Triglyceride digestion

• 3 fatty acids bound to glycerol backbone

• enzymes in digestive trace (lipases) break down triglyceride and release free fatty acids

Lipid digestion & absorption (b)

Enterohepatic Circulation of Bile

• made in the liver, stored in the gall bladder

• emulsifies fat, allowing enzymes to hydrolyze it into smaller units that can be absorbed

• greenish fluid containing:

  • bile salts: derived from cholesterol

  • phospholipids (e.g. lecithin)

  • cholesterol

  • bile pigments

• bile secretion stimulated by CCK

Lipids in the Body: Absorption & Transport

• in the enterocyte:

  • short & medium chain FA (<14 C chain) enter portal circulation

  • long chain FA reassembled into TG

    • combined w/ cholesterol, phospholipids & small protein

    • you now have a lipoprotein called a chylomicron

    • chylomicrons enter the lymph then the bloodstream

Lipoprotein

• transport lipids & cholesterol in the blood

Lipoproteins: lipids in the blood circulation (transport dietary lipids)

• chylomicrons

• very low-density lipoproteins (VLDL)

• intermediate-density (IDL)

• low-density lipoproteins (LDL) - CHD risk

• high-density lipoproteins (HDL) - protective

• protein components (apolipoproteins) involved in metabolism & final disposition of lipoprotein

Cardiovascular Disease (CVD)

• abnormal condition of the heart & blood vessels

• atherosclerosis:

  • narrowing & hardening of blood vessels that supply blood to the heart muscle, brain & other parts of the body

• coronary heart disease (CHD)

  • heart not receiving enough blood

• stroke

  • brain not receiving enough blood

Triglycerides are continuously stored & then broken down, depending on the immediate energy needs of the body

Micronutrients

• vitamins & minerals (trace metals)

• recognition of the need for more than macromolecules in the diet about 120 years ago

• Funk - discovered vital amines

• McCollum - discovered fat soluble A and water soluble B

Water-Soluble Vitamins

• Dissolve in water

• No real stores

• Readily excreted

• Function: coenzymes & antioxidants

• Absorbed by portal system

• Not required daily

• High doses can be toxic

• Subject to cooking & food storage losses

• Examples:

  • B vitamins

    • Thiamin

    • Riboflavin

    • Niacin

    • Biotin

    • Pantothenic acid

    • Vitamin B

    • Folate

  • Vitamin C

Fat-Soluble Vitamins

• Fat soluble

• Stored in tissues

• Remain in adipose & liver

• Function: hormones, blood clotting, antioxidants

• Absorbed by lymphatic system w/ fats (chylomicrons)

• Not required daily

• High doses can be toxic

• Examples:

  • Vitamin A

  • Vitamin D

  • Vitamin E

  • Vitamin K