Chapter Notes for Lecture: E.N. Marieb, HUMAN ANATOMY & PHYSIOLOGY,5TH Edition, , Benjamine Cummings Publisher, 2001 Prepare from : V.A. Austin’s PowerPpoint Presentation (ISBN: 0-8053-5469-7), CD ROM: Pearson Education, Inc. , 2003.

 

Chapter 25

Nutrition, Metabolism, and Body Temperature Regulation

Nutrition

•      Nutrient – a substance that promotes normal growth, maintenance, and repair

•      Major nutrients – carbohydrates, lipids, and proteins

•      Other nutrients – vitamins and minerals (and technically speaking, water)

•      Grains, fruits, vegetables, meats and fish, and milk products

Carbohydrates

•      Complex carbohydrates (starches) are found in bread, cereal, flour, pasta, nuts, and potatoes

•      Simple carbohydrates (sugars) are found in soft drinks, candy, fruit, and ice cream

•      Glucose is the molecule ultimately used by body cells to make ATP

•      Neurons and RBCs rely almost entirely upon glucose to supply their energy needs

•      Excess glucose is converted to glycogen or fat and stored

•      The minimum amount of carbohydrates needed to maintain adequate blood glucose levels is 100 grams per day

•      Starchy foods and milk have nutrients such as vitamins and minerals in addition to complex carbohydrates

•      Refined carbohydrate foods (candy and soft drinks) provide energy sources only and are referred to as “empty calories”

Lipids

•      The most abundant dietary lipids, triglycerides, are found in both animal and plant foods

•      Essential fatty acids – linoleic and linolenic acid, found in most vegetables, must be ingested

•      Dietary fats:

•    Help the body to absorb vitamins

•    Are a major energy fuel of hepatocytes and skeletal muscle

•    Are a component of myelin sheaths and all cell membranes

•      Fatty deposits in adipose tissue provide:

•    A protective cushion around body organs

•    An insulating layer beneath the skin

•    An easy-to-store concentrated source of energy

•      Prostaglandins function in:

•    Smooth muscle contraction

•    Control of blood pressure

•    Inflammation

•      Cholesterol stabilizes membranes and is a precursor of bile salts and steroid hormones

Lipids: Dietary Requirements

•      Higher for infants and children than for adults

•      The American Heart Association suggests that:

•    Fats should represent less than 30% of one’s total caloric intake

•    Saturated fats should be limited to 10% or less of one’s total fat intake

•    Daily cholesterol intake should not exceed 200 mg

Proteins

•      Complete proteins that meet all the body’s amino acid needs are found in eggs, milk, milk products, meat, and fish

•      Incomplete proteins are found in legumes, nuts, seeds, grains, and vegetables

•      Proteins supply:

•    Essential amino acids, the building blocks for nonessential amino acids

•    Nitrogen for nonprotein nitrogen-containing substances

•      Daily intake should be approximately 0.8g/kg of body weight

Proteins: Synthesis and Hydrolysis

•      All-or-none rule

•    All amino acids needed must be present at the same time for protein synthesis to occur

•      Adequacy of caloric intake

•    Protein will be used as fuel if there is insufficient carbohydrate or fat available

•      Nitrogen balance

•    The rate of protein synthesis equals the rate of breakdown and loss

•    Positive – synthesis exceeds breakdown (normal in children and tissue repair)

•    Negative – breakdown exceeds synthesis (e.g., stress, burns, infection, or injury)

•      Hormonal control

•    Anabolic hormones accelerate protein synthesis

Vitamins

•      Organic compounds needed for growth and good health

•      They are crucial in helping the body use nutrients and often function as coenzymes

•      Only vitamins D, K, and B are synthesized in the body; all others must be ingested

•      Water-soluble vitamins (B-complex and C) are absorbed in the gastrointestinal tract

•    B12 additionally requires gastric intrinsic factor to be absorbed

•      Fat-soluble vitamins (A, D, E, and K) bind to ingested lipids and are absorbed with their digestion products

•      Vitamins A, C, and E also act in an antioxidant cascade

Minerals

•      Seven minerals are required in moderate amounts

•    Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium

•      Dozens are required in trace amounts

•      Minerals work with nutrients to ensure proper body functioning

•      Calcium, phosphorus, and magnesium salts harden bone

•      Sodium and chloride help maintain normal osmolarity, water balance, and are essential in nerve and muscle function

•      Uptake and excretion must be balanced to prevent toxic overload

Metabolism

•      Metabolism – all chemical reactions necessary to maintain life

•      Cellular respiration – food fuels are broken down within cells and some of the energy is captured to produce ATP

•    Anabolic reactions – synthesis of larger molecules from smaller ones

•    Catabolic reactions – hydrolysis of complex structures into simpler ones

•      Enzymes shift the high-energy phosphate groups of ATP to other molecules

•      These phosphorylated molecules are activated to perform cellular functions

Stages of Metabolism

•      Energy-containing nutrients are processed in three major stages

•    Digestion – breakdown of food; nutrients are transported to tissues

•    Anabolism and formation of catabolic intermediates where nutrients are:

•   Built into lipids, proteins, and glycogen

•   Broken down by catabolic pathways to pyruvic acid and acetyl CoA

•    Oxidative breakdown – nutrients are catabolized to carbon dioxide, water, and ATP

Oxidation-Reduction Reaction

•      Oxidation occurs via the gain of oxygen or the loss of hydrogen

•      Whenever one substance is oxidized, another substance is reduced

•      Oxidized substances lose energy

•      Reduced substances gain energy

•      Coenzymes act as hydrogen (or electron) acceptors

•      Two important coenzymes are nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD)

Mechanisms of ATP Synthesis: Substrate-Level Phosphorylation

•      High-energy phosphate groups are transferred directly from phosphorylated substrates to ADP

•      ATP is synthesized via substrate level phosphorylation in glycolysis and the Krebs cycle

Mechanisms of ATP Synthesis: Oxidative Phosphorylation

•      Uses the chemiosmotic process whereby the movement of substances across a membrane is coupled to chemical reactions

•      Is carried out by the electron transport proteins in the cristae of the mitochondria

•    Nutrient energy is used to pump hydrogen ions into the intermembrane space

•    A steep diffusion gradient across the membrane results

•    When hydrogen ions flow back across the membrane through ATP synthase, energy is captured and attaches phosphate groups to ADP (to make ATP)

Carbohydrate Metabolism

•      Since all carbohydrates are transformed into glucose, it is essentially glucose metabolism

•      Oxidation of glucose is shown by the overall reaction:

 

C6H12O6 + 6O2 ΰ 6H2O + 6CO2 + 36ATP + heat

 

•      Occurs in three pathways

•    Glycolysis

•    Krebs cycle

•    The electron transport chain and oxidative phosphorylation

Glycolysis

•      A three-phase pathway in which:

•    Glucose is oxidized into pyruvic acid

•    NAD+ is reduced to NADH + H+

•    ATP is synthesized by substrate-level phosphorylation

•      Pyruvic acid:

•    Moves on to the Krebs cycle in an aerobic pathway

•    Is reduced to lactic acid in an anaerobic environment

Glycolysis: Phase 1 and 2

•      Sugar activation

•    Two ATP molecules activate glucose into
fructose-1,6-diphosphate

•      Sugar cleavage 

•    Fructose-1,6-diphosphate is cleaved into two 3-carbon isomers

•   Dihydroxyacetone phosphate

•   Glyceraldehyde 3-phosphate

Glycolysis: Phase 3

•      Oxidation and ATP formation

•    The 3-carbon sugars are oxidized (reducing NAD+)

•    Inorganic phosphate groups (Pi) are attached to each oxidized fragment

•    The terminal phosphates are cleaved and captured by ADP to form four ATP molecules    

•      The final products are: 

•    Two pyruvic acid molecules

•    Two reduced NAD+ (NADH + H+) molecules

•    A net gain of two ATP molecules

Krebs Cycle: Preparatory Step

Occurs in mitochondrial matrix and is fueled by pyruvic acid and fatty

•      Pyruvic acid is converted to acetyl CoA in three main steps:

•    Decarboxylation

•   Carbon is removed from pyruvic acid

•   Carbon dioxide  is released

•    Oxidation

•   Hydrogen atoms are removed from pyruvic acid

•   NAD+ is reduced to NADH + H+

•    Formation of acetyl CoA – the resultant acetic acid is combined with coenzyme        A, a sulfur-containing coenzyme, to form acetyl CoA

Krebs Cycle

•      An eight-step cycle in which acetic acid is decarboxylated and oxidized, generating: 

•    Three molecules of NADH + H+

•    One molecule of FADH2

•    Two molecules of CO2

•    One molecule of ATP

•      For each molecule of glucose entering glycolysis, two molecules of acetyl CoA enter the Krebs cycle

Electron Transport Chain

•      Food (glucose) is oxidized and the hydrogen:

•    Are transported by coenzymes NADH and FADH2

•    Enter a chain of proteins bound to metal atoms (cofactors)

•    Combine with molecular oxygen to form water

•    Release energy

•      The energy released is harnessed to attach inorganic phosphate groups (Pi) to ADP, making ATP by oxidative phosphorylation

Hypothetical Mechanism of Oxidative Phosphorylation

•      The hydrogens delivered to the chain are split into protons (H+) and electrons

•    The protons are pumped across the inner mitochondrial membrane by:

•   NADH dehydrogenase (FMN, Fe-S)

•   Cytochrome b-c1

•   Cytochrome oxidase (a-a3)

•    The electrons are shuttled from one acceptor to the next

•      Electrons are delivered to oxygen, forming oxygen ions

•      Oxygen ions attract H+ to form water

•      H+ pumped to the intermembrane space:

•    Diffuses back to the matrix via ATP synthase

•    Releases energy to make ATP

Electronic Energy Gradient

•      The transfer of energy from NADH + H+ and FADH2 to oxygen releases large amounts of energy

•      This energy is released in a stepwise manner through the electron transport chain

•      The electrochemical proton gradient across the inner membrane:

•    Creates a pH gradient 

•    Generates a voltage gradient

•      These gradients cause H+ to flow back into the matrix via ATP synthase

Summary of ATP Production

Glycogenesis and Glycogenolysis

•      Glycogenesis – formation of glycogen when glucose supplies exceed cellular need for ATP synthesis

•      Glycogenolysis – breakdown of glycogen in response to low blood glucose

Gluconeogenesis

•      The process of forming sugar from noncarbohydrate molecules

•      Takes place mainly in the liver

•      Protects the body, especially the brain, from the damaging effects of hypoglycemia by ensuring ATP synthesis can continue

Lipid Metabolism

•      Most products of fat metabolism are transported in lymph as chylomicrons

•      Lipids in chylomicrons are hydrolyzed by plasma enzymes and absorbed by cells

•      Only neutral fats are routinely oxidized for energy

•      Catabolism of fats involves two separate pathways

•    Glycerol pathway

•    Fatty acids pathway

•      Glycerol is converted to glyceraldehyde phosphate

•    Glyceraldehyde is ultimately converted into acetyl CoA

•    Acetyl CoA enters the Krebs cycle

•      Fatty acids undergo beta oxidation which produces:

•    Two-carbon acetic acid fragments, which enter the Krebs cycle

•    Reduced coenzymes, which enter the electron transport chain

Lipogenesis and Lipolysis

•      Excess dietary glycerol and fatty acids undergo lipogenesis to form triglycerides

•      Glucose is easily converted into fat since acetyl CoA is:

•    An intermediate in glucose catabolism

•    The starting molecule for the synthesis of fatty acids

•      Lipolysis, the breakdown of stored fat, is essentially lipogenesis in reverse

•      Oxaloacetic acid is necessary for the complete oxidation of fat

•    Without it, acetyl CoA is converted into ketones (ketogenesis)

Lipid Metabolism: Synthesis of Structural Materials

•      Phospholipids are important components of myelin and cell membranes

•      The liver:

•    Synthesizes lipoproteins for transport of cholesterol and fats

•    Makes tissue factor, a clotting factor

•    Synthesizes cholesterol for acetyl CoA

•    Uses cholesterol for forming bile salts

•      Certain endocrine organs use cholesterol for synthesizing steroid hormones

Protein Metabolism

•      Excess dietary protein results in amino acids being:

•    Oxidized for energy

•    Converted into fat for storage

•      Amino acids must be deaminated prior to oxidation for energy

•      Deaminated amino acids are converted into:

•    Pyruvic acid

•    One of the keto acid intermediates of the Krebs cycle

•      These events occur as transamination, oxidative deamination, and keto acid modification

Oxidation of Amino Acids

•      Transamination – switching of an amine group from an amino acid to a keto acid (usually a-ketoglutaric acid of the Krebs cycle)

•    Typically, glutamic acid is formed in this process

•      Oxidative deamination – the amine group of glutamic acid is:

•    Released as ammonia

•    Combined with carbon dioxide in the liver

•    Excreted as urea by the kidneys

•      Keto acid modification – keto acids from transamination are altered to produce metabolites that can enter the Krebs cycle

Synthesis of Proteins

•      Amino acids are the most important anabolic nutrients, which form:

•    All protein structures

•    The bulk of the body’s functional molecules

•      Amounts and types of proteins:

•    Are hormonally controlled

•    Reflect each life cycle stage

•      A complete set of amino acids is necessary for protein synthesis

•    All essential amino acids must be provided in the diet

State of the Body

•      The body exists in a dynamic catabolic-anabolic state

•      Organic molecules (except DNA) are continuously broken down and rebuilt

•      The body’s total supply of nutrients constitutes its nutrient pool

•      Amino acid pool – body’s total supply of free amino acids is the source for:

•    Resynthesizing body proteins

•    Forming amino acid derivatives

•    Gluconeogenesis

Interconversion Pathways of Nutrients

•      Carbohydrates are easily and frequently converted into fats

•      Their pools are linked by key intermediates

•      They differ from the amino acid pool in that:

•    Fats and carbohydrates are oxidized directly to produce energy

•    Excess carbohydrate and fat can be stored

Absorptive and Postabsorptive States

•      Metabolic controls equalize blood concentrations of nutrients between two states

•      Absorptive

•    The time during and shortly after nutrient intake

•      Postabsorptive

•    The time when the GI tract is empty

•    Energy sources are supplied by the breakdown of body reserves

Absorptive State

•      The major metabolic thrust is anabolism and energy storage

•    Amino acids become proteins

•    Glycerol and fatty acids are converted to triglycerides

•    Glucose is stored as glycogen

•      Dietary glucose is the major energy fuel

•      Excess amino acids are deaminated and used for energy or stored as fat in the liver

Principal Pathways of the Absorptive State

•      In muscle

•    Amino acids become protein

•    Glucose is converted to glycogen

•      In the liver

•    Amino acids become protein or are deaminated to keto acids

•    Glucose is stored as glycogen or converted to fat

•      In adipose tissue

•    Glucose and fats are converted and stored as fat

•      All tissues use glucose to synthesize ATP

Insulin Effects on Metabolism

•      Insulin controls the absorptive state and its secretion is stimulated by:

•    Increased blood glucose

•    Elevated amino acid levels in the blood

•    Gastrin, CCK, and secretin

•      Insulin enhances:

•    Active transport of amino acids into tissue cells

•    Facilitated diffusion of glucose into tissue

Diabetes Mellitus

•      A consequence of inadequate insulin production or abnormal insulin receptors

•      Glucose becomes unavailable to most body cells

•      Metabolic acidosis, protein wasting, and weight loss results as fats and tissue proteins are used for energy

Postabsorptive State

•      The major metabolic thrust is catabolism and replacement of fuels in the blood

•    Proteins are broken down to amino acids

•    Triglycerides are turned into glycerol and fatty acids

•    Glycogen becomes glucose

•      Glucose is provided by glycogenolysis and gluconeogenesis

•      Fatty acids and ketones are the major energy fuels

•      Amino acids are converted to glucose in the liver

Principle Pathways in the Postabsorptive State

•      In muscle:

•    Protein is broken down to amino acids

•    Glycogen is converted to ATP and pyruvic acid (lactic acid in anaerobic states)

•      In the liver:

•    Amino acids, pyruvic acid, stored glycogen, and fat are converted into glucose

•    Fat is converted into keto acids that are used to make ATP

•      Fatty acids (from adipose tissue) and ketone bodies (from the liver) are used in most tissue to make ATP

•      Glucose from the liver is used by the nervous system to generate ATP

Hormonal and Neural Controls of the Postabsorptive State

•      Decreased plasma glucose concentration and rising amino acid levels stimulate alpha cells of the pancreas to secrete glucagon (the antagonist of insulin)

•      Glucagon stimulates:

•    Glycogenolysis and gluconeogenesis

•    Fat breakdown in adipose tissue

•    Glucose sparing

•      In response to low plasma glucose, the sympathetic nervous system releases epinephrine, which acts on the liver, skeletal muscle, and adipose tissue to mobilize fat and promote glycogenolysis

Liver Metabolism

•      Hepatocytes carry out over 500 intricate metabolic functions

•      A brief summary of liver functions

•    Packages fatty acids to be stored and transported

•    Synthesizes plasma proteins

•    Forms nonessential amino acids

•    Converts ammonia from deamination to urea

•    Stores glucose as glycogen, and regulates blood glucose homeostasis

•    Stores vitamins, conserves iron, degrades hormones, and detoxifies substances

Cholesterol

•      Is the structural basis of bile salts, steroid hormones, and vitamin D

•      Makes up part of the hedgehog (Hh) molecule that directs embryonic development

•      Is transported to and from tissues via lipoproteins

•      Lipoproteins are classified as:

•    HDLs –
high-density lipoproteins have more protein content

•    LDLs –
low-density lipoproteins have a considerable cholesterol component

•    VLDLs –
very low density lipoproteins are mostly triglycerides

Lipoproteins

•      The liver is the main source of VLDLs, which transport triglycerides to peripheral tissues (especially adipose)

•      LDLs transport cholesterol to the peripheral tissues and regulate cholesterol synthesis

•      HDLs transport excess cholesterol from peripheral tissues to the liver

•    Also serve the needs of steroid-producing organs (ovaries and adrenal glands)

•      High levels of HDL are thought to protect against heart attack

•      High levels of LDL, especially lipoprotein (a), increase the risk of heart attack

Plasma Cholesterol Levels

•      The liver produces cholesterol:

•    At a basal level of cholesterol regardless of dietary intake

•    Via a negative feedback loop involving serum cholesterol levels

•    In response to saturated fatty acids

•      Fatty acids regulate excretion of cholesterol

•    Unsaturated fatty acids enhance excretion

•    Saturated fatty acids inhibit excretion

•      Certain unsaturated fatty acids (omega-3 fatty acids, found in cold-water fish) lower the proportions of saturated fats and cholesterol

Non-Dietary Factors Effecting Cholesterol

•      Stress, cigarette smoking, and coffee drinking increase LDL levels

•      Aerobic exercise increases HDL levels

•      Body shape is correlated with cholesterol levels

•    Fat carried on the upper body is correlated with high cholesterol levels

•    Fat carried on the hips and thighs is correlated with lower levels

Body Energy Balance

•      Bond energy released from catabolized food must equal the total energy output

•      Energy intake – equal to the energy liberated during the oxidation of food

•      Energy output includes the energy:

•    Immediately lost as heat (about 60% of the total)

•    Used to do work (driven by ATP)

•    Stored in the form of fat and glycogen

•      Nearly all energy derived from food is eventually converted to heat

•      Cells cannot use this energy to do work, but the heat:

•    Warms the tissues and blood

•    Helps maintain the homeostatic body temperature

•    Allows metabolic reactions to occur efficiently

Regulation of Food Intake

•      When energy intake and energy outflow are balanced, body weight remains stable

•      The hypothalamus releases peptides that influence feeding behavior

•    Orexins are powerful appetite enhancers

•    Neuropeptide Y causes a craving for carbohydrates

•    Galanin produces a craving for fats

•    GLP-1 and serotonin make us feel full and satisfied

Feeding Behaviors

•      Feeding behavior and hunger depends on one or more of five factors

•    Neural signals from the digestive tract

•    Bloodborne signals related to the body energy stores

•    Hormones, body temperature, and psychological factors

Nutrient Signals Related to Energy Stores

•      High plasma levels of nutrients that signal depressed eating

•    Plasma glucose levels

•    Amino acids in the plasma

•    Fatty acids and leptin

Hormones, Temperature, and Psychological Factors

•      Glucagon and epinephrine stimulate hunger

•      Insulin and cholecystokinin depress hunger

•      Increased body temperature may inhibit eating behavior

•      Psychological factors that have little to do with caloric balance can also influence eating behaviors

Control of Feeding Behavior and Satiety

•      Leptin, secreted by fat tissue, appears to be the overall satiety signal

•    Acts on the ventromedial hypothalamus

•    Controls appetite and energy output

•    Suppresses the secretion of neuropeptide Y, a potent appetite stimulant

•      Blood levels of insulin and glucocorticoids play a role in regulating leptin release

Metabolic Rate

•      Rate of energy output (expressed per hour) equal to the total heat produced by:

•    All the chemical reactions in the body

•    The mechanical work of the body

•      Measured directly with a calorimeter or indirectly with a respirometer

•      Basal metabolic rate (BMR)

•    Reflects the energy the body needs to perform its most essential activities

•      Total metabolic rate (TMR)

•    Total rate of kilocalorie consumption to fuel all ongoing activities

Factors that Influence BMR

•      Surface area, age, gender, stress, and hormones

•      As the ratio of surface area to volume increases, BMR increases

•      Males have a disproportionately high BMR

•      Stress increases BMR

•      Thyroxine increases oxygen consumption, cellular respiration, and BMR

Regulation of Body Temperature

•      Body temperature – balance between heat production and heat loss

•      At rest, the liver, heart, brain, and endocrine organs account for most heat production

•      During vigorous exercise, heat production from skeletal muscles can increase 30–40 times

•      Normal body temperature is 36.2°C (98.2°F); optimal enzyme activity occurs at this temperature

•      Temperature spikes above this range denature proteins and depress neurons

Core and Shell Temperature

•      Organs in the core (within the skull, thoracic, and abdominal cavities) have the highest temperature

•      The shell, essentially the skin, has the lowest temperature

•      Blood serves as the major agent of heat transfer between the core and shell

•      Core temperature remains relatively constant, while shell temperature fluctuates substantially
(20°C–40°C)

Mechanisms of Heat Exchange

•      The body uses four mechanisms of heat exchange

•    Radiation – loss of heat in the form of infrared rays

•    Conduction – transfer of heat by direct contact

•    Convection – transfer of heat to the surrounding air

•    Evaporation – heat loss due to the evaporation of water from the lungs, mouth mucosa, and skin (insensible heat loss)

•      Evaporative heat loss becomes sensible when body temperature rises and sweating produces increased water for vaporization

Role of the Hypothalamus

•      The main thermoregulation center is the preoptic region of the hypothalamus

•      The heat-loss and heat-promoting centers comprise the thermoregulatory centers

•      The hypothalamus:

•    Receives input from thermoreceptors in the skin and core

•    Responds by initiating appropriate heat-loss and heat-promoting activities

Heat-Promoting Mechanisms

•      Low external temperature or low temperature of circulating blood activates heat-promoting centers of the hypothalamus to cause:

•    Vasoconstriction of cutaneous blood vessels

•    Increased metabolic rate

•    Shivering

•    Enhanced thyroxine release

Heat-Loss Mechanisms

•      When the core temperature rises, the heat-loss center is activated to cause:

•    Vasodilation of cutaneous blood vessels

•    Enhanced sweating

•      Voluntary measures commonly taken to reduce body heat include:

•    Reducing activity and seeking a cooler environment

•    Wearing light-colored and loose-fitting clothing

Mechanisms of Body Temperature Regulation

Hyperthermia

•      Normal heat loss processes become ineffective and elevated body temperatures depress the hypothalamus

•      This sets up a positive-feedback mechanism, sharply increasing body temperature and metabolic rate

•      This condition, called heat stroke, can be fatal if not corrected

Heat Exhaustion

•      Heat-associated collapse after vigorous exercise, evidenced by elevated body temperature, mental confusion, and fainting

•      Due to dehydration and low blood pressure

•      Heat-loss mechanisms are fully functional

•      Can progress to heat stroke if the body is not cooled and rehydrated

Fever

•      Controlled hyperthermia, often a result of infection, cancer, allergic reactions, or central nervous system injuries

•      White blood cells, injured tissue cells, and macrophages release pyrogens that act on the hypothalamus, causing the release of prostaglandins

•      Prostaglandins reset the hypothalamic thermostat

•      The higher set point is maintained until the natural body defenses reverse the disease process

Developmental Aspects

•      Good nutrition is essential in utero as well as throughout life

•      Lack of proteins needed for fetal growth and in the first three years of life can lead to mental deficits and learning disorders

•      With the exception of insulin-dependent diabetes mellitus, children free of genetic disorders rarely exhibit metabolic problems

•      In later years, non-insulin-dependent diabetes mellitus becomes a major problem

•      Many agents prescribed for age-related medical problems influence nutrition

•    Diuretics can cause hypokalemia by promoting potassium loss

•    Antibiotics can interfere with food absorption

•    Mineral oil interferes with absorption of fat-soluble vitamins

•    Excessive alcohol consumption leads to malabsorption problems, certain vitamin and mineral deficiencies, deranged metabolism, and damage to the liver and pancreas