Macronutrients: digestion and absorption Flashcards
what acute and chronic illnesses is a vitamin D deficiency associated with?
preeclampsia
childhood dental caries
periodontitis
autoimmune disease
infectious diseases
cardiovascular disease
deadly cancers
type 2 diabetes
neurological disorders
what does vitamin D do for the teeth?
absorbs, carries and deposits calcium in the bones
what does a lack of vitamin D lead to in the teeth?
dental caries
weak and brittle teeth that easily break chip and crack
what is the % reduction of cavities in children that take vitamin D supplements?
47%
what are the primary reasons for nutrient imbalances?
inadequate intake, malabsorption and nutrient wasting
what medical conditions can a nutrient imbalance result in?
chrons disease
cystic fibrosis
bariatric surgery
parental and tube feeding
allergic states
HIV infection
malignancies
what are renal and hepatic diseases and what do they lead to?
Alter protein storage and lead to nutritional deficiency
what social factors contribute to insufficient nutritional intake?
poverty
homelessness
famine
war
what is the difference between free sugar and not free sugar?
free sugar = monosaccharides/ disaccharides ADDED to the food or sugar naturally present in honey, syrups and unsweetened fruit juices and fruit juice concentrates
not free sugar = sugar NATURALLY PRESENT in intact fruits and lactose naturally present in human milk, formula, cow/goat milk, unsweetened milk products
what type of sugar increases the risk of obesity, diabetes, poor nutrient supply and dental caries?
free sugars
what do non starch polysaccharides do in the GIT?
absorb water > faecal bulking > increases transit time
what are NSPs fuel for?
bacterial metabolism
what are 3 common characteristics of dietary fibre?
- saccharides of plant origin
- resistance to digestion and absorption in the small intestine
- fermentation in the colon to produce short chain of fatty acids that are absorbed and metabolised in various pars of the body
what short chain fatty acids are produced from the fermentation of NSPs?
acetic acid
propionic acids
butyric acid
what are oligosaccharides?
non digestible polysaccharides
dietary fibre
what are fructans?
inulin and oligofructose
(mix of oligosaccharides and polysaccharides composed of fructose)
inulin and oligofructose are not hydrolysed or absorbed in the upper GIT. what happens to them?
reach colon and become either totally, patially or not fermented.
what ferments inulin and oligofructose in the colon?
microflora
what does the fermentation of inulin and oligofructose in the colon lead to?
selective simulation of the growth go the bifidobacteria population
why are inulin and oligofructose termed prebiotics?
nondigestible good ingredients that selectively stimulate growth and activity of a number of potentially health stimulating intestinal bacteria
name 3 natural sources of inulin and oligofructose?
chicory roots
Jerusalem artichokes
garlic
what is the recommended daily intake of dietary fibres in most countries (not western)?
25-35g
what is hydrolysis in terms of carb digestion?
- basic process of digestion
- major types of macronutrients in food are primarily digested by hydrolysis
what must happen to polysaccharides and disaccharides prior to them being absorbed?
they must be digested to monosaccharides
describe the digestion process of starch?
first digested by amylase in pancreatic secretions (and saliva) to maltose, maltriose and limit dextrins
disaccharides require brush border hydrolyses. what are these?
maltose - cleaves maltose unto 2 molecules of glucose
lactase - cleaves lactose into a glucose and a galactose
sucrase - cleaves sucrose into a glucose and a fructose
what happens to polysaccharides in the GIT?
- starches digested to maltose and glucose units, absorbed as glucose in SI
- NSP digested in LI and absorbed as SCFA
what happens to oligosaccharides in the GIT?
digested in LI and absorbed as SCFA
what happens to mono and disaccharides in the GIT?
digested and absorbed in small intestine as monosaccharides
do monosaccharides eg. glucose and fructose in fruits need to be digested?
no they are absorbable carbohydrates
what is a lactose intolerance?
loss of lactase at weaning
- lactose not hydrolysed, passes to bowel and metabolised to SCFA, gases
how do you diagnose a lactose intolerance ?
H2 in breath for lactose malabsorption
what is a secondary lactose intolerance?
infection, illness - reduced lactase expression
what are GLUT transporters?
- all facilitated (passive transporters)
- 12 members
what are SGLT (sodium glucose transport) transporters?
- active transporters that need sodium
- move glucose from low to high conc
how are sugar transported regulated?
dietary CHO bioavailability
what is the transport capacity of human intestines?
10kg of monosaccharides per day
what are the metabolic and hormonal responses after meal intake?
- increases blood glucose
- intakes blood TG
- decreases blood NEFA
- decreases B-hydroxybutryrate
- increase insulin
*decreases glucagon
what is the fate of dietary carbohydrates?
- glucose uptake by muscles
- liver and muscle glycogen synthesis
- oxidative disposal of glucose in muscle and other tissues
what is the definition of fats?
solid at room temp
- refers to dietary triacylglycerols (triglycerides)
what is the definition of oil?
liquid at room temp
what is the definition of lipid?
group of water insoluble compounds of which trycylglycerols are the major form in diet
what are the main dietary lipids?
- triacylglycerols or triglycerides 90-95%
= glycerol and 3 fatty acids - phospholipids
= phosphorus + 2 fatty acids (lecithin) - sterols
= derived from fatty acids (cholesterol)
how do the presence of double bonds structurally effect the properties of fatty acids?
- saturated and unsaturated fatty acids
- cis and trans isomers
- position of the double bond
what is a saturated fat?
no double bonds present so all C atoms are fully saturated with H atoms
what are the 2 types of unsaturated fat?
monounsaturated = 1 double bond
eg. olive oil, rapeseed oil
polyunsaturated =>1 double bond
eg. sunflower oil
what are cis fats?
configuration of double bonds in naturally occurring unsaturated fats
eg. veg oil
what are trans fats?
have 1 double bond
- industrially produced - ‘partially or fully hydrogenated’
- naturally occurring - meat/dairy & produced by action of bacteria in stomach
what is TAG digestion?
emulsification by bile acids and formation of small micelles
hydrolyses of TAG by pancreatic lipase
what problems are there with fat digestion?
fat is insoluble in water
enzymes in aqueous phase
- need to bring both together to break up fat
what are some emulsifying agents?
fatty acids
monoglycerides
cholesterol
lecithin
protein
bile acids
what happens during micelle formation?
bile acids with fatty acids
- at critical micellar concentration
2-5mmol/l from mixed micelles
- bile acids coat lipid soluble material with water soluble skin
what is the structure of a micelle?
- polar head = hydrophilic
- non polar hydrocarbon tail = hydrophobic
- hydrophobic lipid core = insoluble long chain fatty acids, 2-monoacylglycerol, tocopherol and carotenoids)
how are fatty acids absorbed?
- at brush border - lower pH at mucosa reduces solubility of lipid in micelles
- fatty acids absorbed by diffusion (but may be a carrier protein)
what fatty acids don’t need micelles?
medium chain fatty acids
when do fatty acids go straight into portal blood?
when they are less than 12 carbons long
what happens if fatty acids are more than 12 carbons long?
triglycerides reformed in cell coating in protein, phospholipid and cholesterol enclosed in vesicles
what side are chylomicrons and how are they secreted?
76-100nm in diameter
secreted into lymphatics via lacteals
what form chylomicrons?
newly formed TAG packed with phospholipids and proteins
- dietary cholesterol cholesterol esters also incorporated into the chylomicrons
what is the composition of newly secreted chylomicrons?
core = TAG, cholesterol esters
surface = unesterified cholesterol, phospholipids, apoproteins B48 and A1
how much of our total protein intake is made up of animal protein foods?
60-70%
how are proteins absorbed?
rarely absorbed whole so are digested into amino acids or di and tripeptides
what does acid do in the digestion of proteins?
- denatures proteins, unfolding the 3D structure
- activates zymogen - pepsinogen to pepsin
- stimulus for proteolytic enzyme secretion
what % of proteins are digested by stomach pepsin?
20%
where are dietary proteins hydrolysed and what do they go into?
within the lumen of the small intestine predominantly into medium and small peptides (oligopeptides )
what does protein digestion rely on?
pancreatic proteases either endopeptidase or exopeptidase
what is endopeptidase?
a pancreatic protease that acts inside the peptide chain
what is exopeptidase?
a pancreatic protease that acts at the extremities of the peptide chain
give an overview of the 3 steps of protein digestion?
proteins to peptides to peptides and amino acids
what type of transporters are majority of the ones involved in amino acid absorption?
what do they depend on?
sodium dependant co transporters
- only bind amino acids after binding sodium
what does amino acid absorption have to do with water absorption?
amino acid absorption generates an osmotic gradient that drives water absorption
what peptides can be absorbed and which can’t?
peptides longer than 4 amino acids will NOT be absorbed
- di and tri peptides are absorbed in the small intestine
how are di and tri peptides digested into amino acids?
by cytoplasmic peptidases
what are the functions of macronutrients?
- provide energy in sufficient quantities
- provide range of building blocks
- provide essential nutrients we can’t make ourselves
how much energy per gram of the following macronutrients in kcal?
- carbs
- fat
- protein
- alcohol
carbs = 4
fat = 9
protein = 4
alcohol = 7
what is the role of essential fatty acids?
- cell membranes
- biologically active compounds
- growth and development
what is the role of dietary fats?
- energy provision
- essential fatty acids
- help carry fat-soluble vitamins
- enables storage of energy
- structural role in cell membranes
- metabolic functions
