Nutritional Science Definitions

• The following list contains a summary of the lecture notes:

Definitions

• Nutrition interprets the interaction of nutrients and other substances in food for maintenance, growth, reproduction, health, and disease
• Nutrition encompasses food intake, absorption, assimilation, biosynthesis, catabolism, and excretion.
• Nutrition Science is a multidisciplinary field studying dietary and health issues, involving chemistry, biology, physiology, neuroscience, psychology, and social sciences
• Calorie: The energy (amount of heat) required to raise 1 gram of water by 1°C.
• Also a tiny measure of heats.
• Calorie (kcal): Equal to 1000 calories
• Commonly used to describe food energy
• Since calorie is a small measure of heat, food energy is more accurately expressed in terms of kilocalorie
• Phytochemicals are physiologically active compounds in plants that offer health benefits but are not essential nutrients; over 1,000 exist
• Zoochemicals are physiologically active compounds in animal products, providing health benefits but are not essential nutrients

Classes of Nutrients

• Macronutrients are needed in large amounts:
• Carbohydrates provide energy; e.g., glucose.
• Lipids (Fats) store energy and serve as structural components; e.g., linoleic acid (omega 6), a=Linolenic acid (omega-3), Histidine, Isoleucine, leucine
• Proteins support growth, repair tissues, and act as enzymes and hormones; e.g., Lysine, methionine, phenylalanine, threonine, tryptophan, valine
• Water is essential for hydration, temperature regulation, and chemical reactions.
• Micronutrients are needed in smaller amounts:
• Vitamins:
• Water-Soluble Vitamins are easily excreted, including B-complex and vitamin C.
• Fat-Soluble Vitamins are stored in fat tissues, including vitamins A, D, E, and K.
• Minerals are inorganic elements required for various bodily functions.
• Water is crucial for life and often considered separately.

Caloric Content

• Fat contains 9 kcal/g
• Carbohydrates contain 4 kcal/g
• Protein contains 4 kcal/g
• Alcohol contains 7 kcal/g

Daily Reference Intakes (DRIs)

• Estimated Average Requirement (EAR): Intake level inadequate for 50% of healthy North Americans.
• Recommended Dietary Allowance (RDA): Intake level sufficient for 97-98% of healthy individuals; 2-3% would have inadequate intake
• Adequate Intake (AI): Set when there is insufficient evidence for an RDA; estimated to cover most individuals
• Lies between RDA and UL ,covers the needs of more than 97 to 98% of individuals
• Tolerable Upper Intake Level (UL): Maximum daily nutrition intake unlikely to cause adverse effects.
• At Intakes between RDA and UL, the risk of either an inadequate diet or adverse effects from nutrient is close to 0%
• Estimated Energy Requirements (EER): Average daily caloric intake needed to maintain energy balance.

Daily Values (DVs)

• DVs are generic nutrient standards developed by the FDA for food labels.
• Unlike DRIs, DVs aren't specific to age or gender and represent needs of individuals over 4 years of age
• Nutrient Facts on Food Labels compare nutrient amounts to Daily Values.

Primary Digestive Organs:

• Mouth: Chews food, digests starch, lubricates food with mucus, has antimicrobial action
• Chewing increases surface area, salivary amylases digest carbohydrates, saliva lubricates, saliva has antimicrobial action
• Esophagus: Transports food via peristalsis waves initiated by swallowing
• Stomach: Stores food, acid kills bacteria, digests protein, activates enzymes
• Secretes HCl to kill bacteria, activates enzymes (e.g., pepsinogen to pepsin), denatures proteins, releases mucus for protection
• Secretes intrinsic factor
• Small Intestine (SI): Completes digestion and absorbs nutrients, divided into duodenum, jejunum, and ileum
  • Cells regenerate every 3-5 days aiding absorption but increasing vulnerability
• Large Intestine: Absorbs water, electrolytes, and minerals; supports microbiome; forms and stores waste; contains many microorganisms.
• Anus: Eliminates waste.

Accessory Digestive Organs:

• Liver: Produces bile for fat digestion, stores glycogen, detoxifies.
• Gallbladder: Stores and releases bile to the small intestine.
• Pancreas: Produces digestive enzymes (lipases, proteases, amylases) and bicarbonate to neutralize stomach acids.

Passage Times in GI Tract:

• Mouth and Esophagus: Few seconds to minutes.
• Stomach: 2-4 hours for mixing and chemical breakdown.
• Small Intestine: 3–10 hours for digestion and absorption.
• Large Intestine: 1–2 days for water absorption and waste solidification.

Hunger vs. Appetite:

• Hunger is primarily physiological.
• Appetite is primarily psychological.

Taste Receptor Tastes:

• Bitter signals potential toxins.
• Salty food detects sodium for fluid balance.
• Sweetness indicates sugar, glucose, sweeteners.
• Umami indicates savory flavors, protein, amino acids.
• Sourness indicates acidity or fermentation.
• Carbonation may detect dissolved CO2.

Taste Buds and TRCs:

• Taste Buds contain clusters of TRCs, each specialized for one taste.
• TRCs (taste receptor cells) project into the taste pore, interact with dissolved food, and send signals to the brain
• Each receptor cell is highly selective for a single taste

Taste Receptor Interactions:

• <100 mM Na attracts humans to food.

• 300mM Na activates sour and bitter receptors causing aversion

• Low salt is attractive; high salt activates bitter and sour receptors; disabling bitter or sour receptors removes aversion to high salt.
• Taste is what is detected by taste buds, with six receptor types
• Flavor combines taste and smell; olfactory receptors enhance flavor perception

Sphincters in GI Tract:

• Upper Esophageal Sphincter allows entry of food into the esophagus; voluntary control.
• Lower Esophageal (Cardiac) Sphincter prevents acid reflux from the stomach.
• Pyloric Sphincter regulates chyme flow from the stomach to the small intestine.
• Ileocecal Sphincter prevents backflow from the large intestine.

Stomach Structure:

• Three layers of muscle (longitudinal, circular, oblique) for mixing and grinding.
• Parietal Cells release HCl, denaturing proteins, and activating enzymes.
• Chief Cells secrete pepsinogen, activated to pepsin by stomach acid for protein digestion.
• Mucous Cells release mucus to protect the stomach lining from acid and pepsin.

Parietal Cell Acidification:

• CO2 + H2O → H2CO3 → H+ + HCO3¯ (catalyzed by carbonic anhydrase).
• H+ is pumped into the stomach lumen by a proton pump.
• Cl ions are transported into the lumen via chloride channels.
• H+ and Cl combine to form HCI in the stomach.

Small Intestine Subsections:

• Duodenum neutralizes acidic chyme with bicarbonate from the pancreas; bile aids fat digestion (10 in.)
• Jejunum is a major nutrient absorption site (4ft).
• Ileum absorbs bile salts and remaining nutrients (5ft).

Chemical Digestion:

• Pancreas produces bicarbonate, lipases, amylases, and proteases (e.g., trypsinogen).
• Liver produces bile to emulsify fats.
• Small intestine produces glycosidases and amylases for carbohydrate digestion.

Intestinal Structures:

• Black center is the lumen.
• Fingerlike villi (red) increase surface area for absorption
• Outer yellow layer is the muscle pushing chyme.
• Epithelial cells have microvilli forming the absorptive brush border

Intestinal Sensitivity:

• Lining regenerates every 3-5 days
• High turnover makes it susceptible to chemotherapy (damages cells), inflammation, and pathogens

Nutrient Absorption by Organ:

• Stomach: Alcohol (small amounts), Water (minimal).
• Small intestine: Macronutrients, vitamins, minerals, water, electrolytes, bile acids.
• Large intestine: Water, electrolytes, short-chain fatty acids, vitamins.

GI Tract Absorption:

• Mouth and Esophagus: Minimal absorption; starch digestion and lubrication of food with mucus.
• Stomach: Absorbs alcohol and drugs (e.g., aspirin), digests food releasing pepsinogen and mucus.
• Small intestine is main absorption site and final digestion site.
• Duodenum and Jejunum: Absorbs carbohydrates, proteins, lipids, calcium, and iron.
• Ileum: Absorbs bile salts, vitamin B12.
• Large intestine: Absorbs water, electrolytes, gut bacteria-produced vitamins.

Hepatic Portal Vein vs. Lymphatic Vessels:

• Hepatic portal vein carries absorbed nutrients (except fats) from the gut DIRECTLY to the liver for processing and detoxification
• Liver stores glycogen/lipids, and detoxifies
• Lymphatic vessels absorb lipids and fat-soluble vitamins, delivering them to the bloodstream. does not directly transport nutrients to the liver but to bloodstream

Accessory Organ Functions:

• Salivary glands produce mucus, amylase, and lysozyme for initial digestion in the mouth via saliva
• Liver produces bile for fat digestion, stores energy (glycogen and lipids), and detoxifies; bile is delivered through bile duct to duodenum.
• Gallbladder stores and releases bile into the duodenum.
• Pancreas produces NaHCO3 and lipases, amylases, and proteases delivered to the duodenum to mix with bile

Bile Acid Functions:

• Act as detergents essential for lipid uptake, enhancing fat digestion and absorption
• Chemical Features: Amphipathic molecules from cholesterol.

GI Tract Secretions:

• Saliva and amylase digests carbohydrates with an antimicrobial function
• Gastric juice including pepsinogen, HCI, and mucus in the stomach
• Pancreatic juice including enzymes and sodium bicarbonate neutralizes stomach acid
• Bile emulsifies fats.

Digestion Regulation:

• Nervous system regulates with autonomic nerves secretion of saliva, swallowing, and gastric secretions
• GI releases hormones (gastrin, secretin, cholecystokinin) in response to specific stimuli

Bayliss and Starling Experiment:

• Demonstrated G.I. tract self-regulation via chemical messengers not nerves
• 1902 study secretin stimulates pancreatic secretion without nerve involvement
• Injected HCl into the intestinal lumen evoking secretion by the pancreas
• Injected the filtered extract elicited copious pancreatic secretion
• Named the chemical secretin and recognized it as a messenger chemical hormone

Hormone Functions:

• Gastrin stimulates HCl secretion triggered by food in the stomach
• Cholecystokinin stimulates bile release and pancreatic enzyme secretion triggered by fats
• Secretin stimulates bicarbonate secretion from the pancreas triggered by acidic chyme

Anabolism vs. Catabolism:

• Anabolism involves building complex molecules (e.g., protein synthesis from amino acids).
• Catabolism involves breaking down molecules for energy (e.g., glycolysis, beta-oxidation).

Catabolic Pathways:

• Carbohydrates: Glycolysis → Krebs cycle → ETC (Glucose oxidation to product ATP)
• Fatty acids: Beta-oxidation → Krebs cycle → ETC
• Proteins: Transaminase reactions → Deamination → Krebs cycle (Proteins digested in stomach where HCl denatures proteins and pepsin break them down)

Glucose to Krebs:

• Glycolysis generates pyruvate → Acetyl-CoA → Krebs cycle (processes molecules and generate ATP)
• ETC: NADH and FADH2 from Krebs transfer electrons to produce ATP.

Fatty Acids and Glucose:

• Fatty acids can not form glucose, because beta-oxidation produces Acetyl-CoA, which cannot be converted to pyruvate due to the irreversible nature of pyruvate dehydrogenase
• Acetyl CoA from fatty acids can enter the Krebs cycle, but cannot be converted back to glucose

Amino Acids:

• Glucogenic amino acids yield glucose.
• Ketogenic amino acids yield ketone bodies.
• Some amino acids are both glucogenic and ketogenic.

Metabolism Sites:

• Carbohydrates: Cytoplasm (glycolysis), mitochondria (Krebs and ETC).
• Fats: Mitochondria (beta-oxidation).
• Proteins: Cytoplasm and mitochondria.

Transaminases in Amino Acid Metabolism:

• Transaminases transfer amino groups, enabling synthesis of non-essential amino acids and connecting protein metabolism with the Krebs cycle.

Glucose Production:

• Lactate produced during anaerobic respiration can be transported to the liver to be converted back into glucose via gluconeogenesis.
• Glycerol (from lipids) can be converted into glucose via gluconeogenesis.
• Certain amino acids (glucogenic) can be converted into intermediates of gluconeogenesis

Vitamin Deficiencies:

• Vitamin deficiencies disrupt multiple pathways
• Causing cofactor disruption leading to widespread dysfunction

Digestive Functions:

• Liver metabolizes carbohydrates, lipids, and amino acids
  • Stores energy
• Detoxifies and contributes to urea production
• Synthesizes bile for digestion and absorption of fats
• Carries out gluconeogenesis and releases glucose into the blood.

Genetic Contributions:

• Garrod linked genetics to metabolic diseases
• Demonstrating that disorders like alkaptonuria are inherited
• work provided a basis for understanding genetic basis of many diseases and highlighted the possibility of using diet to treat conditions like alkaptonuria (defect in tyrosine metabolism)

Fölling and PKU:

• Identified phenylketonuria as a genetic metabolic disorder that when deficient in enzyme phenylalanine hydroxylase occurs causes toxic phenylalanine buildup.
• Can be managed through dietary intervention (restricting phenylalanine and supplementing tyrosine)

Fructose, Glucose, and Galactose:

• Fructose is a naturally occurring simple sugar. It is sweeter than glucose.
• A primary source of energy source for cells; commonly found in blood and derived from carbohydrates.
• A simple sugar often found in milk and dairy products

Sugar Structure:

• Linear forms are the linear chain of carbon atoms attached to oxygen and hydrogen in the rings.
• Alpha and beta anomers result from the orientation of the hydroxyl at teh Carbon-1; opposing Hydroxyl (alpha) or Hydroxyl to the same (beta)

Disaccharides:

• Sucrose is glucose + fructose, linked by an a-1,2 bond.
• Lactose is glucose + galactose, linked by a ẞ-1,4 bond.
• Maltose is two glucose molecules, linked by an a-1,4 bond.
• Raffinose is a trisaccharide of galactose, glucose, and fructose
• Raffinose is undigestible by small intestine enzymes due to its a-galactosidic bond, which humans lack the enzyme to break down

Supplements:

• Beano contains alpha-galactosidase, breaking down raffinose to digestible sugars
• Alleviating gas and bloating

Polysaccharides:

• Starch is a plant energy storage with a-1,4 and a-1,6 bonds. Easily digestible by human amylases
• Glycogen is branched polymer of glucose with a-1,4 and a-1,6 bonds; energy stored in animals’ liver and muscle tissue
• Cellulose is an insoluble fiber with ß-1,4 bonds, indigestible by humans due to lack of cellulase

Glycogen Stores:

• Liver stores ~100 g glycogen used to maintain blood glucose.
• Muscles store ~350 g glycogen used locally for energy during activity

GI Organs and Carbohydrates:

• In the mouth, amylase begins to break down complex carbohydrates.
• In the stomach, there's no carbohydrate digestion because amylase is inactivated.
• In the small intestine, pancreatic amylase continues starch digestion.
• Brush border enzymes break disaccharides into monosaccharides.
• In the large intestine with gut microbiota fermentation of carbohydrates occur

Glucose Transporters:

• SGLT1 (apical membrane) actively transports glucose into gut cells with Na+.
• GLUT2 (basolateral membrane) moves glucose from cytoplasm to bloodstream through facilitated diffusion.

Glycogen:

• Liver glycogen maintains blood glucose during fasting
• Muscle glycogen provides energy for muscle activity without blood release
• Glycogen and glucose availability prevents ketosis during activity

Prolonged Starvation:

• Includes glycogen depletion (24 hours), lipid and protein breakdown (3-4 days), and ketone body production for brain energy (after 1 week)
• 3-5 days = SI lining regeneration

Hormones:

• Insulin promotes sugar uptake, glycogen synthesis, and fat storage in pancrea’s beta cell, with inhibits lipolysis hormones
• Glucagon stimulates glycogen breakdown, gluconeogenesis, and fat mobilization in the liver’s alpha cell with stimulated lipolysis hormones

Dietary Fibers:

• Insoluble fiber increases stool bulk.
• Soluble fiber forms gels dissolving digestion and decreasing caloric waste

Low Glucose States:

• Fatty acids undergo B-oxidation, producing acetyl-CoA
• Excess acetyl-CoA is converted into ketone bodies in the liver

Glycemic Index

• GI= a test of blood in comparison to 50 g comparable of change in blood.
• GL=(GI/100) with carb.

Increase Glucose Consumption

• Increased use of high fructose corn syrup and processed goods in the USA over past 100 years, which is the top contributor to sugar in said diet

Artificial Sweeteners

• May cause imbalances in micro biome and decrease satiety
• May cause diabetes

Fibers Impact to Health

• Can bulk/soften stoops , increasing gut health
• Can also reduce chance of Hemorrhoids

Binds Glucose/Cholesterol

May slow absorption, and aid in diabetes's

Protein Digestion:

• Enzymes in the stomach (pepsin) and small intestine (trypsin, chymotrypsin) break proteins into polypeptides, amino acids, dipeptides, and tripeptides for absorbtion

Irritable Bowel Syndrome cause and effects

• IBS is a chronic condition characterized by frequent discomforts and gas in gut
• Causes a higher chance of fluid in areas such as bowel.

Amino Acid Functions

• Protein Synthesis to aid in muscles
• Provides energy through fuel
• Provides signal through the muscles

High vs. Low Protein

• Increases Gut Lining impairing function
• Increases inflammation

Vitamin A

• Is crucial to lower acid.

Small intestine Regeneration

• A small intestine lining can regenerate every 3- 5 days.