HAP_Chapter 24(1)Nutrition, Metabolism, and Energy Balance
24 Nutrition, Metabolism, and Energy Balance
1. Introduction
Understanding nutrition is crucial for optimizing health and performance. This includes recognizing how the body converts various nutrients into energy, and how this process can influence dietary choices.
2. Nutrients
2.1 Definition
Nutrient: Essential substances obtained from food that are necessary for the growth, maintenance, and repair of bodily tissues and systems.
2.2 Categories
Macronutrients (needed in large amounts):
Carbohydrates: Primary source of energy.
Lipids: Used for long-term energy storage and cellular structure.
Proteins: Vital for growth and repair, and enzyme production.
Micronutrients (needed in smaller amounts):
Vitamins: Organic compounds that support metabolic processes.
Minerals: Inorganic elements that play roles in various physiological functions.
most are used for metabolic fuel, and others for building molecules and cells.
Water: Essential for life, comprising about 60% of body weight, aiding in digestion and nutrient transport.
2.3 Essential Nutrients
Essential Nutrients: Nutrients that must be obtained through diet because the body cannot produce them in sufficient quantities. Examples include certain amino acids, fatty acids, vitamins, and minerals. Metabolic interconversions allow the body to utilize different types of molecules, optimizing energy production.
40 molecules must be providedby your diet
liver cells have the ability to convert one type of molecule to another
2.4 Energy Value
Energy from nutrients is measured in kilocalories (kcal).
Calculation: 1 kcal raises the temperature of 1 kg of water by 1°C.
Energy Content per Gram:
Carbohydrates: 4 kcal/g
Proteins: 4 kcal/g
Lipids: 9 kcal/gUnderstanding these values is integral for energy balance and weight management.
2.5 Dietary Guidelines
The USDA MyPlate Guidelines offer a visual representation of food groups and portion sizes for a balanced diet
Food Groups: Include Fruits, Vegetables, Grains, Protein, and Dairy.
Dietary principles:
Consume only as much food as needed to meet energy requirements.
Prioritize nutrient-rich foods, particularly fruits, vegetables, legumes, whole grains, and lean proteins.
Limit consumption of processed foods high in added sugars and unhealthy fats.
3. Macronutrients
3.1 Carbohydrates
Sources: Primarily derived from plant foods, Sugars, Starch, Insoluble and Soluble Fiber (e.g., grains like rice and wheat, fruits, vegetables, and legumes,sugarcane).
Functions: Glucose, derived from carbohydrates, serves as the primary energy source for ATP production in cells. Excess carbohydrates can be stored as glycogen in the liver and muscles or converted to fat.
Fructose and galactose are converted to glucose before entering circulation
Recommendations: 45-65% of total caloric intake should come from carbohydrates, with an emphasis on complex carbs (e.g., whole grains, legumes).
3.2 Lipids
Sources: Obtained from dietary fats, including triglycerides found in Saturated fats(meat,dairy), Trans fats(hydrogenated oils), and Unsaturated fats(nuts, oils).
Cholesterol is need but liver makes 85% of blood cholesterol
Essential fatty acids that the liver cannt make are; Linoleic acid, and Linolenic
Functions: Provide (energy storage,insulation)(Adipose), structural components of cell membranes (phospholipids), and hormonal functions.
Triglycerides area a major energy source for skeletal muscle and liver cells
Recommendations: 20-35% of total caloric intake should come from fats; limit saturated fats to less than 10% of total fat intake to promote heart health. Cholesterol can be taken in small amounts to prevent cardio vascular diseases.
3.3 Proteins
Sources: Include animal products (which provide complete proteins) and plant-based sources (which may require combination for full amino acid profiles).
Functions: Essential for building and repairing tissues, producing enzymes, and regulating hormones. In times of energy deficit, proteins can be metabolized for energy. Essential amino acids must be acquired through the diet.
Multiple factors determine whether amino acids in cell are used to synthesize new proteins or used for energy (to make ATP):
The all-or-none rule: all amino acids needed to build a particularprotein must be present at the same time
If one or more are insufficient, protein can’t be made, and itsamino acids are instead used as energy or converted to carbsor fats
Adequacy of caloric intake: food and body proteins used asenergy when intake of carbohydrate or fat calories are insufficient forATP needs
Hormonal controls: anabolic hormones like GH and gonadalsteroids promote protein synthesis; other hormones likeglucocorticoids promote protein breakdown and conversion of aminoacids to glucose
Nitrogen Balance
Homeostatic state where rate of protein synthesis equals rate ofbreakdown and loss; amount of nitrogen ingested (via protein) equal samount excreted
Positive nitrogen balance: synthesis exceeds breakdown
Normal in growing children, pregnant women, tissue repair
Negative nitrogen balance: breakdown for energy exceeds synthesis
Occurs during stress, burns, infection, injury, low quality or quantity
Recommendations: Vary based on factors like age, sex, and physical activity level; an average intake is about 0.8 g of protein per kg of body weight.
4. Vitamins and Minerals
4.1 Vitamins
Definition: Organic compounds required in minute amounts to facilitate energy metabolism and maintain health. They do not provide calories but are essential for turning macronutrients into energy.
Most are coenzymes, which act woth an enzyme to carry out a particular reaction
Most are ingested but D, B, and K
D (made in skin)
B and K (synthesized by intestinal bacteria)
Types:
Water-soluble: These include B vitamins and vitamin C; they are easily absorbed and not stored in the body, requiring daily intake.
ANY absorbed but not used are excreted in the urine
Fat-soluble: Includes vitamins A, D, E, and K; these can accumulate in the body and excessive intake can lead to health problems.
4.2 Minerals
Essential Minerals: Includes
Calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium
Functions: Calcium and phosphorus are crucial for bone health; iron is essential for oxygen transport in the blood; sufficient intake and proper balance of these minerals are vital for overall health.Sodium and chloride are major electrolytes in blood and Iodine is necessary for thyroid synthesis
5. Metabolism
5.1 Overview
Metabolism: Refers to the sum of all biochemical processes within the body. Includes
Catabolism: The breakdown of complex molecules into simpler ones.
Anabolism: The synthesis of larger molecules or structures from smaller ones, requiring energy. Energy from food oxidation fuels these metabolic processes and is critical for cellular activities and thermogenesis.
Sustances are constantly built up (anabolism) and broken down (catabolism)
Three major stages involved in processing energy-containing nutrients:
Stage 1: digestion and absorption in gastrointestinal tract
Stage 2: in cytoplasm, newly delivered nutrients either:
Built into lipids, proteins, and glycogen by anabolic pathways
Broken down by catabolic pathways to smaller fragments
Stage 3: in mitochondria, complete breakdown of stage 2 products (mostwill first be converted into acetyl C o A)
Uses oxygen
Produces carbon dioxide, water, and large amounts of ATP
Cellular respiration: Group of catabolic reactions that covert some of the chemical energy of nutrients into a form of chemical energy ATP cells cann use to do work
Phosphorlation: tranafer of highenergy phosphate group from ATP to another molecule
Body stores energy as glycogen or triglycerides , then breaks them don later to produce ATP for cellular use
Oxidation Reduction Reactions and the Role of CoEnzymes
Many reactions in cells are oxidation reactions which refers to when there is a gain of oxygen and a loss of hydrogen
this substance will always lose their electronsas they move towards another substance that attracts them
Oxygen-reduction (redox) reactions: when substances loses their electrons (oxydized) another gains them in return (reduced)
Redox reactions enzymes;
Dehydrogenases: catalyze removal of hydrogen atoms
Oxidases: catalyze transfer of oxygen
Most redox enzymes require a B vitamin coenzyme
Nicotinamide adenine dinucleotid (NAD+)
Flavin adenine dinucleotide (FAD)
5.3 ATP Production
Cellular Respiration: The process of converting the chemical energy in nutrients into ATP through:
Substrate level phosphorylation is the direct transfer of high level phosphate group from substrate to ADP
twice in glycolysis and once in krebs cycle
Oxidative phosphorylation more complex and produces more ATP
Two Steps:
Electron Transport Chain (ETC): Involves aerobic respiration, producing the majority of ATP. ~50% of energy released via nutrient oxidation used to pump Hl across inner membrane, creating steep [H+] gradient
Chemiosmosis: coupling movement of Hl (diffusion down gradient) acrossselectively permeable membrane to a chemical reaction—the synthesis of ATP
Diffusion of Hl across inner membrane through protein ATP synthaseprovides energy to attach phosphate groups to ADP, making ATP
Carbohydrate metabolism is the central player in ATP production as carbohydrates are converted onto glucose
glucose enter cells and phosphorylates into glucoses -6- phosphate
only cells in intestine,kidney,liver,can reverse reaction and release glucose
Glucose catabolism/ oxidation of glucose
Glycolysis: Occurs in the cytosol, does not require oxygen (anaerobic).
Citric acid cycle
Oxidative phosphorylation
Glycolisis: Converts each glucose to two pyrubate molecules
three major phases
Sugar phase
sugar cleavage
Sugar Oxidaiton and ATP formation
Final product of glycolysis; 2 molecules of pyruvate, 2 reduced NAD+, and has a net gainn of 2 ATP
When oxygen is insufficient, NADH + H+ unloads its H atoms backonto pyruvate and this reduce it to lactate
this lactate enter the blood and is picekd up by the liver to be converted back into glucose-6-phosphate which is then converted to glucose and released into blood or stored as glycogen
Citric Acid Cycle(Krebs Cycle): Takes place in the mitochondria matrix fuled by pyruvate and fatty acids from fat breakdown
transitional phase converts pyruvate to acetyl CoA via three step prpcess;
Decarboxylation: 1 carbon from pyruvate is removed, producinggas, which diffuses into blood to be expelled by lungs
Oxidation: remaining 2-C fragment oxidized to acetate by removal of Hatoms, which are picked up by NAD+
Formation of acetyl CoA: acetate combines with coenzyme A to formacetyl coenzyme A (acetyl CoA
Citric acid cycle makes 2 molecules of CO2, 4 moecules of coenzymes 3 NADH and 1 FADH2, and 1 molecule of ATP(GTP)
Oxidative Phosphorylation: This process is more complex and produces more ATP than substrate-level phosphorylation. It consists of two steps:
Electron Transport Chain (ETC): This involves aerobic respiration, producing the majority of ATP. About 50% of the energy released via nutrient oxidation is used to pump H+ across the inner mitochondrial membrane, creating a steep H+ gradient.
Chemiosmosis: This process couples the movement of H+ (diffusion down the gradient) across a selectively permeable membrane to a chemical reaction—the synthesis of ATP. The diffusion of H+ across the inner membrane through the protein ATP synthase provides energy to attach phosphate groups to ADP, resulting in ATP formation.
ETC involves chain of carrier protiens embedded in inner mitochondrial membrane
flavins - protiens derived from riboflavin
cytochromes - protiens with iron contian pigment
respiratory enzyme complexes - clusters of neigborhing carriers that are alternatley reduced and oxidized as they pass electrons down the chain, ultimately facilitating the production of ATP through oxidative phosphorylation.
Phosphorylation: The process of transferring a phosphate group to ADP to create ATP via substrate-level and oxidative phosphorylation.
6. Homeostatic imbalence
hydrogen cyanide binds to cytchrome oxidase and blocks electron flow from complex iv to oxygen
uncouoplers destroy proton gradient by making inner mitochondrial membrane permeable to H+
Glycogenesis, Glycogenolysis, andGluconeogensis
cells nannot store large amounts of ATP, eventually inhibiting glucose catabolism and promotoing its storage as glycogen or fat
Glycogenesis - is the synthesis of glycogen from glucose molecules, primarily occurring in the liver and muscle tissues, allowing for energy storage during periods of excess glucose availability.
Glycogenolysis - glycogen breakdown to realese stored glucosefor energy production, especially during fasting or intense physical activity, ensuring that the body maintains adequate glucose levels for cellular functions.
Gluconeogenesis - the process of synthesizing glucose from non-carbohydrate precursors, such as amino acids and glycerol, which typically occurs in the liver and is crucial during prolonged fasting or low-carbohydrate diets to ensure a continuous supply of glucose for vital metabolic activities.
Lipid Metabolism Is Key for Long-Term Energy Storage and Release
fats are the most concentrated spurce of energy in the body, most products of fat digestion are transported in lymph (to blood) via chylomicrons\
Oxidation of Glycerol and Fatty Acids
triglycerides only lipids routiney oxidized for energy; thier building blocks oxidized seperatley
fattyacids undergo beta-oxidation in the mitochondria, producing acetyl-CoA, which enters the citric acid cycle to generate ATP.Glycerol can also be converted into glucose through gluconeogenesis, allowing it to contribute to energy production during periods of fasting or intense exercise.
Lipogenesis - triglyceride synthesis; stimulatedn bu high glucose levels and cellular ATP
acetyl CoA molecules are joinstogether to form fatty acids, which can be stored as triglycerides in adipose tissue for later use. These fattty acids chains grow two cardons at a time
Glucose easily converted to fat because acetyl CoA is also the starting point for fatty acif synthesis
Lipolysis - breakdown of stored fats into glycerol and fatty acids
thee fatty acids preferred fuel of liver, cardiac muscle, resting skeletal muscle
lipolysis accelerated when carbohyrate intake inadequate to fill fuel gap
excess acetyl CoA converted by ketogenesis in liver to ketone bodies
Synthesis of structural materials
all cell bodies use phospholipids and cholesterol to build their membranes, as well as myelin sheaths of neurons
the liver synthesises lipoprotiens to transports cholesterol, fats, other substances in blood
Protiens has limited life span, must be broken down and replced before deteriorating, and the amino acids released during this process can be recycled to synthesize new proteins or converted into other compounds necessary for cellular functions.
replace tissue protiens at a rate of ~100g/day
Protiens are not stored in the body, amino acids in excess are oxidezed for energy or converted to fat or glycogen for storage
Fed and Fasting State
Hormonal control of the fed state
insulin directs essentially events of the fed state, its secretion is stimulated by;
elevated blood glucose levels, amino acids in circulation, and the presence of GI tract hormones such as lucose-dependent insulinotropic peptide (GIP), and parasympathetic stimulation
Insulin facilitates glucose uptake by cells, promoting glycogenesis and lipogenesis, while simultaneously inhibiting gluconeogenesis and lipolysis.
brain and liver take up glucose without insulin
Insulin is a blood glucose lowering (hypoglycemic hormone that enhances;
glucose storage in the liver and muscle tissues, and facilitates the conversion of excess glucose into fatty acids for long-term energy storage.
Diabetes mellitus - disorder of inadequate insulin production or abnormal insulin productioon or abnormal insulin receptors
glucose levels remain high as most cells need insulin for glucoe entry
large amounts of glucose excreted in urine (carrying out large amounts of water with it)
Results in metabolic acidosis, protien wasting andweight loss as large amounts of fats and tissue proteins used for energy
Fasting state
postabsorptive state, is when GI tract is empty and energy stores are broken down to meet bodys metabolic demands
goal is usually to maintaib blood glucose within normal range (70-110mg glucose per 100ml)
Sources of blood glucose
Glycogenoysis in the liver , Glycogenlysis in skeletal muscle, lipolysis in adipose tissue and the liver, catabolism of cellular protein
Glucose sparing - during prolonged fasting the body uses more noncarbohydrate fuels to conserve glucose, the brain uses the bulk (ketone as well as glucose after 4-5 days) of it while the other body cells switch to fatty acids as main fuel
hormonal and nueral controls of the fasting state; hormones and sympathetic nervous system interact to control events of fasting state
Hormones such as glucagon and epinephrine promote glycogenolysis and gluconeogenesis to maintain blood glucose levels.
The sympathetic nervous system enhances lipolysis and the release of free fatty acids, providing alternative energy sources during fasting. Additionally, cortisol plays a significant role by increasing protein catabolism, which contributes to gluconeogenesis, ensuring that the body has enough glucose available for critical functions. In contrast, insulin levels decrease, reducing glucose uptake in non-essential tissues, further facilitating the shift towards fat utilization for energy.
sympathetic nervous system - sympathetic fibers innervate various organs, including the liver and adipose tissue, to modulate metabolic responses during fasting. These adaptations allow the body to prioritize energy conservation and mobilization of stored nutrients, ensuring survival during prolonged periods without food.
6.1 Homeostasis
Maintaining homeostasis involves balancing the energy input (food consumption) with energy output (metabolic processes, physical activity). An imbalance can lead to weight loss or obesity, which can be assessed using Body Mass Index (BMI).
6.2 Regulation of Food Intake PG 100
“RIGHT HERE”
Food intake is tightly regulated by a network of neural and hormonal signals that govern hunger and satiety.
Hormones such as insulin (signals high energy storage) and leptin (signals satiety) are critical in regulating energy storage and expenditure, influencing eating behavior and metabolic rate.
7. Conclusion
An in-depth understanding of nutrition and metabolism is essential for promoting healthier dietary choices and optimizing performance and health outcomes.