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Page 67: Fiber and Lipids

Insoluble Fibers

  • Definition: Poorly or non-fermentable fibers, primarily cellulose and lignin.

    • Role: Promote colonic health by:

      • Increasing fecal volume.

      • Exerting a detoxifying effect by adsorbing hydrophobic carcinogens, preventing interaction with colonic mucosa and facilitating excretion.

Fiber Intake Recommendations

  • Health Canada: Daily reference value of 25 g for a 2000 kcal energy intake.

  • RDI:

    • 38 g/day for young men.

    • 25 g/day for young women.

  • WHO Recommendation: 25 g to 40 g daily for adults.

Sources of Dietary Fiber

  • Whole grain products: 1 to 2 g of fiber/serving.

  • Vegetables: 2 to 3 g of fiber/serving.

  • Fruits: About 2 g of fiber/serving.

  • Legumes: 6 to 8 g of fiber/serving.

Page 68: Fiber Types and Effects

Types of Fiber

  • Soluble Fiber:

    • Sources: Fruits, legumes, oats.

  • Insoluble Fiber:

    • Sources: Cereals, grains, nuts, and some vegetables.

  • Examples:

    • Pectin: Soluble.

    • Cellulose and Hemicellulose: Insoluble.

    • Gums and Mucilages: Soluble.

    • Lignin: Insoluble.

Effects of Fiber on Digestion

  • Impact on Nutrient Dynamics:

    • Delays stomach emptying and alters small intestine transit time.

    • Enhances mixing of GI contents with digestive enzymes as well as their function, facilitating nutrient diffusion and absorption of lipids.

    • Affects nutrient diffusion and reduces glycemic response to food.

    • Influences lipid absorption and bile acid excretion, reducing cholesterolemia.

  • Fermentation: Soluble fibers ferment to produce SCFAs (short-chain fatty acids), like acetic, butyric, and propionic acids, beneficial for colonic health(Mostly done in cecum and ascending colon).

Effects of SCFAs on the GI Tract

  • Stimulate water and sodium absorption in the colon.

  • Promote colon mucosal cell health (differentiation and proliferation).

  • Lower pH, reducing bile solubility and increasing calcium binding to bile and fatty acids.

  • Protective against colon cancer and energy source for colonic cells.

  • Inhibit hepatic cholesterol synthesis and enhance immune function.

Page 69: Gut Microbiota and Dietary Fiber

Gut Microbiota

  • Definition: An assemblage of microbes in a habitat; approximately 39 trillion bacterial cells inhabit the human body.

  • Composition: Comprises various microorganisms, with bacteria vastly outnumbering other types.

  • Colonic Role: Breakdown dietary fibers, resistant starches, and non-carbohydrate substrates, producing SCFAs, which provide energy and nutritional benefits to the host.

  • Production of Short chain fatty acids provides energy to colonic cells contribute 10% caloric intake 95% of SCFAs used by colonic cells as source of energy. SCFAs serve as messengers between microbiota and immune system(Plays role in development and function of intestinal epithelial cells and leukocytes)

Vitamins Production by Gut Bacteria

  • Produce B vitamins (thiamine, riboflavin, niacin, biotin, pantothenic acid, and folate) and vitamin K.

  • Vitamins from diet are absorbed in the small intestine; microbe-produced vitamins are absorbed in the colon.

Definitions of Dietary Fiber

  • Dietary Fiber: Non-digestible carbohydrates and lignin intrinsic to plants.

  • Functional Fiber: Isolated non-digestible carbohydrates with health benefits.

  • Total Fiber Intake: Sum of dietary and functional fibers consumed.

Page 70: Sugar Intake Guidelines

Recommended Sugar Intake

  • 2015 US Dietary Guidelines: Less than 10% of total daily energy intake, primarily from fruits and whole grains.

  • National Obesity Forum (UK): Optimum sugar consumption should be zero.

Glycemic Index (GI)

  • Definition: Measures how much a food increases blood glucose levels, calculated over a 2-hour period post-ingestion of 50 g of digestible carbohydrates.

  • Practical Use of GI: It aids in obesity prevention and diabetes management, though implementation can be challenging due to variations based on individual diets.

  • Glycemic Load (GL): A practical approach that normalizes GI to serving sizes. relevant for obesity prevention and diabetes management.

Page 71: Metabolic Needs of the Brain

Brain Metabolism

  • Blood-brain Barrier isolates brain from lipid soluble molecules and relies primarily on glucose for energy.

  • Energy Requirement: The brain relies heavily on glucose as its primary energy source; oxidation of glucose accounts for high oxygen consumption rates.

  • Transport Mechanisms: Glucose enters the brain via GLUT3 (neurons) and GLUT1 (blood-brain barrier) transporters, independent of insulin.

  • Impairment: Mental function declines when glycemia drops below 2 mmol/l.

Sources of Sugar

  • Composition of Foods: Breakdown of sugars in various food types, showing the percentage from fruits, vegetables, snacks, beverages, grains, etc.

Page 72: Brain Structure and Nutrient Supply

Brain Composition and Blood Supply

  • Glucose and its derivatives (galactose and fructose) enter enterocytes via sodium-dependent co-transport (SGLT1) and facilitated diffusion (GLUT2 and GLUT5). Once inside the enterocytes, glucose is then transported into the bloodstream through the basolateral membrane by the glucose transporter GLUT2, ensuring a steady supply of glucose for energy production in various tissues, including the brain.

  • Liver needs insulin to say what to do with glucose, but not to take it in, as hepatocytes can uptake glucose through GLUT2 without the need for insulin. Insulin primarily regulates the conversion of glucose into glycogen for storage, as well as its utilization for energy production.

  • The brain, however, relies on GLUT1 for glucose uptake from the bloodstream, which is crucial for maintaining its energy demands, especially under conditions of low glucose availability. GLUT4 inside of the cell in vesicle, waiting for signal to come from insulin.

  • Brain requires approx. 120g of glucose/day, constituting ~20% of the body's energy requirements.

Page 73: Digestion of Carbohydrates

Structure of Cellulose

  • Composition: Cellulose, a polysaccharide of glucose, is resistant to human digestion due to its structure (β(1-4) glycosidic bonds).

Carbohydrate Digestion Process

  • Enzymatic Action: Carbohydrates are hydrolyzed by glycosidases and carbohydrases, primarily in the small intestine.

  • Key Enzymes:

    • Enzymes named glycosidases or carbohydrases hydrolyse CHO

    • Begins in the small intestine with pancreatic amylase, primarily affecting polysaccharides like amylopectin, still leaving difficult-to-hydrolyze bonds at branch points. In the duodenum, pH is elevated by bicarbonate to a level that optimizes alpha-amylase activity, allowing polysaccharides in the chyme to be digested in steps.

    • Enzymes like glucoamylase and disaccharidases (e.g., lactase, sucrase) facilitate the breakdown of oligosaccharides and disaccharides for absorption.

    • Amylopectin —> Oligosaccharides(about 8 glucose units, dextrins), Maltose(Disaccharide), Maltotriose(Trisaccharide)—> alpha-amylase(can’t hydrolyze alpha1-4 and 1-6 bonds next to branch points)

    • Alpha-limit dextrinase(glucoamylase): Removes 1 glucose unit from ends of linear alpha1-4-glucosyl chains of dextrins and produce isomaltose(disaccharide with 1 unit attached by alpha1-6 glycolytic bond)

    • Alpha1-6-glucosidase: hydrolyzes alpha1-4 bonds

    • Disaccharidases: hydrolyzes disaccharides

Page 74: Starch Composition

Types of Starch

  • Glucose, Fructose, Galactose(Same as glucose, except HO is upwards which makes it so that different enzymes deal with it) first enter through liver(Converts fructose and galactose into glucose)

  • Amylose: Linear structure (α(1-4) glycosidic bonds).

  • Amylopectin & Glycogen: Branched structures with both α(1-4) and α(1-6) glycosidic bonds.

  • Content in Foods: Cereal grains, potatoes, legumes, and vegetables provide a mix of amylose and amylopectin (80-85% amylopectin, 15-20% amylose).

Page 75: Carbohydrate Classifications

Major Types of Carbohydrates

  • Carbohydrates are categorized based on their molecular structures:

    • Monosaccharides: Simple sugars (e.g., glucose, fructose).

    • Disaccharides: Composed of two monosaccharides (e.g., sucrose, lactose).

    • Oligosaccharides: 3-10 monosaccharides (e.g., stachyose, raffinose).

    • Polysaccharides: >10 monosaccharides (e.g., starch, glycogen, fiber and resistant starch(cellulose, pectin, hemicellulose), glycosaminoglycans).

Inaccessibility to Human Enzymes

  • Certain oligosaccharides (e.g., stachyose, verbacose and raffinose found in beans, peas, bran and whole grains) are not hydrolyzed by human digestive enzymes, often resulting in fermentation by gut bacteria, causing flatulence.

Page 76: Large Intestine Functions

Role of the Large Intestine

  • The large intestine has no villi and primarily absorbs water and electrolytes, processing about 5-7 liters of fluid daily.

  • Feces composition: 30% bacteria, 10-20% fat, 10% inorganic matter, and 30% undigested fibers.

  • Dries and stores undigested material present in the chyme. Additionally, it plays a crucial role in the fermentation of undigested carbohydrates by gut bacteria, producing short-chain fatty acids that provide energy to the colonic cells.

Microbiota Functions

  • Houses over 400 bacterial species capable of producing vitamin K, biotin, and SCFAs beneficial for colonic health.

  • Probiotics: Beneficial bacteria in foods (e.g., yogurt).

  • Prebiotics: Non-digestible food components (e.g., fiber) that enhance beneficial bacterial growth.

Page 77: Pancreatic Function

Pancreas Overview

  • The pancreas secretes juices rich in bicarbonate, electrolytes, and digestive enzymes, regulated by hormones such as secretin and cholecystokinin (CCK).

  • Key enzymes include:

    • Proteases (e.g., trypsinogen, chymotrypsinogen) for protein and CHO digestion(About 50% of the amount ingested).

    • Alpha-Amylase for carbohydrate digestion.

    • Pancreatic lipase for fat digestion, breaking down ~80-90% of dietary fats.

    • Turns enzyme secretion on/off based on the presence of specific substrates in the digestive tract, ensuring efficient digestion and nutrient absorption.

Page 78: Bile Function

Bile Acids/Salts

  • Definition: Emulsifying agents for fat digestion, converting large fat globules into smaller droplets.

  • Function: Facilitates excretion of non-urinary substances (e.g., bilirubin).

Gallbladder Role

  • Storage: Concentrates bile and releases it into the small intestine upon eating, triggered by CCK.

  • Gallstones: Formed from supersaturated bile, causing potential blockages and inflammation.

Page 79: Bile Production by Liver

Overview of Nutrient Pathways

  • Nutrients pass through enterocytes into the portal vein and lymphatics for distribution.

  • The liver intricate role: produces bile and plays a central role in metabolism, detoxification, and nutrient absorption.

Bile Acid Composition

  • Major components include bile acids (chenodeoxycholic and cholic acids), with conjugation occurring with amino acids to form bile salts, aiding in digestion.

Page 80: Vitamins

Definition and Classification

  • Vitamins: Organic compounds necessary for physiological functions, existing as water-soluble or fat-soluble types.

  • Essential for various chemical reactions and cannot be synthesized in adequate amounts by the body.

  • Exceptions: Vitamin D, K, and biotin can be partially sourced from body synthesis (e.g., via gut bacteria).

Importance of Water

  • Water is a critical nutrient, essential for survival, significantly more than any other nutrient. Intracellular volume(60%), Extracellular volume(40%), Interstitial volume(28% of 40), Plasma volume(8% of 40), Transcellular volume(4% of 40), and Total body water (about 60% of body weight) play vital roles in maintaining homeostasis, regulating temperature, and facilitating various biochemical reactions.

Page 81: Gastric Acid Secretion Phases

Gastric Acid Secretion

  • Phases:

    • Cephalic: Triggered by sensory stimuli (30% of acid secretion).

    • Gastric: Activated by food distension and nutrient detection (60%).

    • Intestinal: Stimulated by intestinal distension (10%).

  • Importance: Acidifies chyme for digestion and pathogen control.

Small Intestine Role

  • Primary Function: Major site for nutrient digestion and absorption, housing highly folded surfaces for increased absorptive area.

Page 82: Structure of Small Intestine

Anatomy of the Small Intestine

  • Key functions: digestion and absorption.

  • Surface area is enlarged through folds, villi, and microvilli, enhancing absorption capabilities significantly.

Enterocyte Functionality

  • Enterocytes renew every 3-5 days, supporting nutrient absorption and maintaining gut barrier integrity.

Page 83: Gastric Acid Secretion Mechanisms

Active Regulation of HCI Production

  • Secreted through three primary signals: acetylcholine, histamine, and gastrin for maximal acid production.

  • Critical for activating digestive enzymes and aiding in iron absorption, while intrinsic factor seats in stomach for vitamin B12 absorption.

Page 84: Stomach Function and Structure

Functions of the Stomach

  • Food Processing: Grinds food into chyme, releases gastric juices for digestion.

  • Acid Protection: Alkaline mucus shields stomach lining from acids and enzymes.

  • Chyme Transport: Controlled release of chyme into the duodenum through peristalsis.

Page 85: Body Fluid Compartments

Estimates for a 73kg Man

  • Breakdown of total body water: intracellular (60%), extracellular (40%), with specific volumes for interstitial and plasma.

Digestive System Overview

  • Major components include oral cavity, esophagus, stomach, small and large intestines, and accessory organs, each contributing to digestion, absorption, and metabolism.

  • Intracellular fluid: Approximately 43.8 liters, playing a crucial role in cellular processes and nutrient transport.

  • Extracellular fluid: Approximately 29.2 liters, divided into interstitial fluid (around 25 liters) and plasma (about 4.2 liters), essential for maintaining homeostasis and facilitating communication between cells.

Page 86: Vitamins and Water

Vitamins Overview

  • Definition: Organic compounds essential for bodily functions at minute amounts.

  • Types: Water-soluble and fat-soluble.

  • Synthesis: Most cannot be synthesized sufficiently by the body, with exceptions (vitamin D, K, and biotin).

Importance of Water

  • Crucial Nutrient: Essential for survival; more critical than any other nutrient.

Page 87: Lipids Overview

Definition and Functions

  • Definition: Compounds that are soluble in organic solvents, including fats, oils, and cholesterol.

  • Functionality:

    • Energy storage and release.

    • Insulation, structural support, and signaling.

    • Carriers for fat-soluble vitamins (A, D, E, and K).

Proteins

  • Definition: Composed of amino acids, critical for cellular structure, functions, enzymes, transport, antibodies, and more.

Essential Fatty Acids

  • Definition: Fatty acids required for bodily functions that the body cannot synthesize (e.g., linoleic and alpha-linolenic acid).

Page 88: Nutrient Classification

Macronutrients vs. Micronutrients

  • Macronutrients: Carbohydrates, proteins, and fats (needed in large amounts).

  • Micronutrients: Vitamins and minerals (needed in smaller quantities).

Carbohydrate Functions

  • Sourced from grains, legumes, fruits, and dairy, primarily as glucose for energy, vital for brain functioning.

  • Dietary fiber is crucial in maintaining GI health without providing substantial energy.

Page 89: Nutrition Science Overview

Nutrition as a Field of Study

  • Focused on nutrient interactions within the body for energy usage, growth, tissue repair, and regulation of bodily functions.

Functions of Nutrition

  • Supporting growth, energy production, and contributing to homeostatic regulation and immune functions, fundamental to human health.

Composition of the Human Body

  • Abundance of Elements:

    • O, C, H, and N are the most prevalent, making up essential molecules in the human body.