macronutrients Flashcards
what affects macronutrients
Macronutrients in dietary patterns can be considered as part of food groups or choices
Recommendations, choices and actual plate
what are carbohydrates
1/3 dietary intake
Similar structures – different forms of hydrocarbons
Soluble in water
Glucose primary monomer
energy store (starch and glycogen)
cellulose - non strach polysaccharide (insoluble, pectin is soluble)
glucose, fructose and galactose absorbed by SI
Function of carbs
Energy substrate (glycolysis and citric acid cycle)
Builds macromolecule
Glycogenesis
Spares proteins and fat
Non starch polysaccharide - Substrate for fermentation in colon, fibre for faecal bulk, excretion of dead cells, increase transit time
what is dietary fat
Triacylglycerol
95% dietary fibre intake
3 fatty acids and a glycogen
Saturated or unsaturated
what are polyunsaturated fatty acids
Essential fatty acids
Linoleic acid - veg and safflower oils
A-linoleic acid - green leafy veg, canola, walnut and soybean oils
Arachidonic acid - meat, poultry and eggs
EPA - oily fish
DHA - oily fish
Functions of dietary fat
TAG primary energy substrate stored in adipose tissues to sustain animals during fasting
Influx of TAG into adipose tissue largely mediated by action of adipose tissue lipoprotein lipase
Upregulated in presence of insulin, fatty acids during fasting
what does fat do in our diet
Enhances flavour, increase palatability, carries essential fat-soluble vitamins A, D, E, K and serves as a component of cell membranes, steroid hormone and vitamin precursors
what are proteins
Dynamic in nature
Require 0.8g per kg a day, 1.2 in older adults
Acute illness demand can exceed this, negative nitrogen balance due to inflammation induced catabolism
dietary to tissue, plasma, amino acid derivative eg NTs, a-keotacid residues for carbon skeletons of AAs (energy metabolism), urea and ammonia
amino acids needed in the body
20 Essential, conditionally non-essential and non-essential
Essential not synthesised in body so dietary requirement
Conditionally non-essential, essential precursor missing and required in certain conditions to meet a short fall eg tyrosine requires phenylalanine
Rapid growth arginine and proline synthesised from glutamine and glutamate in intestines
Hyper catabolic states (eg sepsis and burns) deplete glutamine
Adaptions to GI tract facilitate different functions
Stomach – acid environment – mucous and bicarbonate ions
Small intestine - peristalsis becomes segmentation to squeeze food against intestinal wall and maximise digestion and absorption
Sequence of sphincters – cardiac, pyloric, ileocaecal valve, internal and external sphincters
Parasympathetic NS important for GI function
Sequence of sphincters
cardiac, pyloric, ileocaecal valve, internal and external sphincters
Brain and buccal cavity role in digestion
Mastication, swallowing, taste (sweet, sour, bitter, salty and umami)
CHO digestion – Salivary amylase – limited activity
Initiates breakdown of starches by catalysing the hydrolysis of polysaccharides into disaccharides
Fat - lingual lipase secreted by serous glands
stomach’s role in fat digestion
stomach has gastric lipase secreted by gastric cells in fundic mucosa. An acid enzyme that doesn’t require bile acid or colipase (pancreas) for optimal functioning
Enzymes important in neonate (up to 50% lipid hydrolysis) and adults (up to 30%)
stomach’s role in protein digestion
chief cells produce pepsinogen converted to pepsin in presence of HCL to turn proteins to peptides. Acid environment denatures and reduces bacterial load.
bile’s role in digestion
bile acids from liver cholic and chenodeoxycholic acid. Molecule amphipathic so act as detergent to solubilise lipids to form mixed micelles
pancreas’ role in digestion
SI – pancreatic lipase secreted alongside co-factor procolipase (activated in intestinal lumen by trypsin, stabilises pancreatic lipase increasing efficiency). Pancreatic lipase hydrolyses TG to form monocyglycerol, fatty acids and glycerol
Pancreatic Proteases
Two primary pancreatic proteases - trypsin and chymotrypsin, synthesized and packaged within secretory vesicles as inactive pro enzymes: trypsinogen and chymotrypsinogen
activated by an enteropeptidase A- enterokinase secreted by the mucosal membrane of duodenum
The secretory vesicles also contain a trypsin inhibitor to serve as a safeguard against trypsinogen converting to trypsin within the pancreas or pancreatic ducts
what does amylase do
A amylase for carb digestion to breakdown starch and glycogen to disaccharides (maltose, sucrose and lactose which are broken down to monosaccharides by their own specific enzymes)
how does absorption occur
Absorption primarily in SI
Blood supply – 9 litres of fluid enter GI tract with 8 litres absorbed through SI
Large SA to maximise secretion and absorption
Brush border with brush border enzymes
Disaccharide digestion
Further digestion by action of brush border enzymes – gluco-amylase, a-dextrinase, sucrase and maltase to form monosaccharides glucose, fructose, galactose
Carb absorption
Limited to monosaccharides Occurs in SI Capacity for fructose limited Na+ symport in and glut 2 out fructose in by glut 5 and out by glut 2
Fat absorption in SI
Water soluble micelles pass through unstirred water overlying microvilli
Monoglycerol and fatty acids cross apical membrane through passive diffusion and lipid protein transporter mechanism
Built to chylomicrons by ER, enter lacteal to go to left thoracic duct
Protein absorption in SI
Pepsin (stomach), trypsin (pancreatic), peptidases (brush border) break down proteins then move to bloodstream by facilitated diffusion from epithelial cells to go to liver by hepatic portal vein
NSP absorption in SI
NSP resistant starch and most oligosaccharides are not digestion and absorbed in SI soluble fibres (pectin/gum) are fermented by bacteria in colon, insoluble fibres make up cellulose in diet microbial fermentation leads to production of CO2, H2, CH4, short chain fatty acids (acetate, enters peripheral circulation, propionate taken up by liver and butyrate used by colonic cells). Enhances microbial growth
what does diet impact
microbiome
agrarian diet inc and western diet dec due to amount of fermentable food, fat, animal protein and refined sugar
