Macronutrients Flashcards
3 types of lipid
Triglycerides
Sterols
Phospholipids
Triglyceride structure
3 fatty acid chains bonded to a glycerol backbone
Key features of saturated fats
Solid at room temperature
Saturated carbon structure
Resistant to oxidation due to stabile nature
Key features of polyunsaturated fats
Liquid at room temperature
Susceptible to spoilage
Can be hydrogenated to trans fats to protect against oxidation, causing them to behave like saturated fats
Sterols
Starting material for bile acids, sex hormones, adrenal hormones and vitamin D
Structural component of cell membranes
Endogenous cholesterol
The liver produces 800 - 1500 mg of cholesterol a day
Exogenous cholesterol
Cholesterol we take in from dietary animal products
Plant sterols importance
Can interfere with cholesterol absorption
Fat digestion - mouth
Salivary glands release lingual lipase
Fat digestion - stomach
Lingual lipase initiates lipid digestion. Muscle contractions disperse fat into smaller droplets which are then exposed to gastric lipase causing some digestion.
Fat digestion - small intestine
Acidic chyme neutralised in duodenum by bicarbonate from pancreatic juice and bile. Bile salts emulsify fat, turning it into small droplets with a large surface area.
3 major emulsifying agents
Bile salts
Lecithin
2-monoacylglycerol
Lipid digestion in small intestine enzymes
Pancreatic lipase
Pancreatic non-specific esterase
Phospholipase A2
Pancreatic lipase
Digests triglycerides to glycerol and free fatty acids
Requires colipase from pancreas to become active
Pancreatic non-specific esterase
Removes fatty acids from a variety of non-triglycerides and non-phospholipids
Phospholipase A2
Removes fatty acid from 2-position on phospholipid
Milk lipase
Important in breast fed human neonate nutrition. Only becomes active in small intestine because it is bile-dependent
Lecithin
Phospholipid present in bile and food membranes
2-monoacylglycerol
Breakdown product from triglyceride
Bile salts are stored in the:
Gallbladder
Bile salt movement
Made by liver, stored in gallbladder
CCK stimulates bile release
Reabsorbed in terminal ileum of small intestine
Reused via enterohepatic circulation
4 major roles of bile salts in fat digestion
Emulsification
Removal of lipid digestion products from emulsified fat droplets
Cofactors required by lipases for activity
Aids absorption of fat products across enterocyte membrane
Chylomicron
Package of lipid digestion, cholesterol, fat soluble vitamins and apolipoproteins. Transport system pass from lacteal in intestinal epithelium to the lymph and eventually the bloodstream.
Chylomicron components are removed:
During circulation as a result of TG hydrolysis
Chylomicron repackaging
As components are removed from the chylomicron they become smaller and denser
Remnants endocytosed by liver
Remaining lipid repackaged into lipoprotein complexes to leave liver
Types of lipoproteins
Chylomicron VLDL IDL LDL HDL
VLDLs are composed primarily of:
Triglycerides
LDLs are composed primarily of:
Cholesterol
HDLs are composed primarily of:
Protein
Foam cells
Residual fractions of LDL bind low affinity scavenger receptors on macrophages. Macrophages phagocytose LDL forming a fatty aggregate called a foam cell which deposit themselves in atherosclerotic plaques
Key roles of proteins
Building material Hormones Enzymes Immune function Fluid balance Transporters Antibodies Energy
9 essential amino acids
Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine
11 non-essential amino acids
Alanine Arginine Asparagine Aspartic acid Cysteine Glutamic acid Glutamine Glycine Proline Serine Tyrosine
2 semi-essential amino acids
Histidine and arginine
AMDR
Acceptable macronutrient distribution rate
24 specific organic compounds we require for health
9 essential amino acids
2 fatty acids
13 vitamins
Two factors that influence protein quality
Protein digestibility
Amino acid composition
Protein digestibility
High in animal protein, lower in plant protein
Higher digestibility means we can gain more amino acids from it through digestion
Can depend on source and also what we eat with the protein
Amino acid composition
Essential amino acids are vital for energy and synthesis of other amino acids. A lack of just 1 EAA limits the action of other EAAs even if they are in abundance - it becomes the limiting factor.
Process of protein digestion
1) Mastication - involves moistening protein rich foods into a bolus
2) HCl denatures food proteins and stimulates pepsinogen —> pepsin cleavage
3) Pepsin catalyses hydrolysis of proteins into smaller polypeptides and amino acids
4) Pancreatic endopeptidases secreted as inactive precursors in small intestine. When activated by enteropeptidase they break polypeptides down into tripeptides, dipeptides and amino acids
5) Remaining peptides break down further into amino acids
Enzyme mediated protein digestion in small intestine
Pancreatic endopeptidases secreted as inactive precursors which are activated by enteropeptidase (which activates trypsinogen first, followed by the other proteases)
Activated endopeptidases cleave polypeptides into peptides and amino acids which are further cleaved into single amino acids by tripeptidases, dipeptidases and aminopeptidases
Pancreatic juice contains procarboxypeptidases which are activated into carboxypeptidases (A and B) which break down the carbon ends of peptides once activated in the lumen of the small intestine
3 pancreatic endopeptidases and their inactive precursors
Trypsin - trypsinogen
Chymotrypsin - chymotrypsinogen
Elastase - pancreatic elastase
Protein absorption
Sodium linked amino acid transporters and sodium linked peptide transporters on enterocyte in the small intestine which are pulled across by the diffusion of Na+. At the same time, Na+/K+ antiporters are moving ions across the enterocyte/blood border to power the Na+ linked symporters
3 key hormones in the protein digestion process
Gastrin (regulates acid secretion in stomach)
Secretin and CCK (regulate pancreatic secretions)
Nitrogen balance
A state of equilibrium where the rate of nitrogen intake is equal to the rate of nitrogen expenditure
Factors causing negative nitrogen balance (degradation > synthesis)
Decreased short term protein intake Starvation Injury, trauma and surgery Illness, infection and burns Cancers Lactation
Factors causing positive nitrogen balance (synthesis > degradation)
Increased short term protein intake
Growth
Pregnancy
Recovery from illness or trauma
Protein Energy Malnutrition
A condition often seen in poor communities characterised by wasted limbs but protruding bellies due to fluid retention around the liver as a result of low protein
3 types of nitrogen excretion
Urea
Uric acid
Creatinine
Types of carbohydrate
Complex (starch and dietary fibre)
Simple (sugars)
Energy that we use most readily
Carbohydrate
Energy that we store the most
Fat
Carbohydrate that makes up plant cell walls
Cellulose
2 basic compounds that make up a carbohydrate
Ketone and aldehyde
3 key monosaccharides
Glucose
Galactose
Fructose
3 key disaccharides
Lactose
Maltose
Sucrose
Sucrose is made of:
Glucose and fructose
Lactose is made of:
Glucose and galactose
Maltose is made of:
Glucose and glucose
Storage polysaccharide in plants
Starch (amylose and amylopectin)
Non-starch polysaccharides
Glucose links can’t be broken so they aren’t digested
Dietary fibre - can be soluble or insoluble
Glycogen
Storage carbohydrate in animals. Stored in liver and muscles, broken down when energy required for rapid glucose release
Soluble fibre
Dissolves in water to form a gel like substance and is easily digested by bacteria in the colon
Commonly found in legumes, psyllium and fruits and vegetables
Insoluble fibre
Not dissolvable in water and is not broken down as easily by bacteria
Responsible for bulking feces for easy passage
Commonly found in whole grains and vegetables
Carbohydrate digestion
1) Salivary alpha amylase hydrolyses starch
2) Breakdown of oligosaccharides to monosaccharides at brush border
3) Monosaccharides absorbed at enterocyte brush border. Non-degraded disaccharides continue into colon where bacteria feed and can cause inflammation
4) Glucose and galactose absorbed by active transport
5) Fructose and galactose isomerised to glucose
High glycaemic index
Blood sugar peaks when lots of simple sugars are consumed. Insulin also peaks to force blood sugar down. Feel hungry due to low blood sugar, eat more sugar causing another spike and so on.
Low glycaemic index
Lower insulin response means you feel full for longer and don’t need to eat as often so less blood sugar and insulin spikes. Increased exercise increase glucose utilisation so not as much insulin needed to push sugar spikes down.
