unit 1 nutrition

carbohydrates 

• monosaccharides - glucose, fructose, galactose

• disaccharides - two monomers linked through glycosidic linkage

  • maltose (2 glucose)

    • alpha 1,4 glycosidic linkage

    • malted grain 

    • partial digestion 

  • sucrose (glucose,fructose)(table sugar)

    • alpha 1-beta-2 glycosidic linkage (unique among carbs)

    • non-reducing

    • consume roughly 100 lbs per year 

    • sources - sugarcane, sugar beets, honey, maple syrup

    • processing of corn starch with enzymes produces high fructose corn syrup

  • lactose (galactose, glucose)

    • beta - 1,4 glycosidic bond

    • milk and milk products 

    • lactose digestion

      • digestion challenges (lactose intolerance)

      • generally lack the ability to hydrolyze beta glycosidic linkages 

        • amylose vs cellulose 

      • start life with ability to digest lactose (enzyme lactase) but many people lose this ability 

        • lactose broken down by gut bacteria, producing CO2 gas 

      • dairy products 

        • less present in hard aged cheese

        • lactose free milk already has lactase added 

• sweetness rank: fructose > sucrose > glucose > galactose > lactose 

• reducing and non reducing ends

  • sugar molecule with the free anomeric C is the reducing end and the other is the non reducing end 

• glycosidic bonds

  • linkage between sugar molecules

  • naming - configuration of anomeric C (alpha/beta) and number (C involved in linkage)

  • formation

    • condensation (water released)

  • breaking

    • hydrolysis (digestion - water is a reactant)

• polysaccharides - amylose, amylopectin, glycogen

• structural forms

  • open (fischer projection) - long chains

  • closed (haworth projection) - rings 

SUMMARY/KEY TAKEAWAYS: small changes in structure between sugars make a lot of difference in their sweetness, their ability to be digested and how they are metabolized 

CARBOHYDRATES 2

• monosaccharides

  • glucose (dextrose), fructose (levulose)

  • double bonded O (aldose vs ketose)

• disaccharides

  • bond orientation (alpha vs beta)

  • reducing and non-reducing ends 

• polysaccharides

  • starches - from plants

    • bead structure

      • amylose - linear chain of alpha 1,4 glucose molecules 

        • 1 reducing end and 1 non-reducing end

      • amylopectin - branching chain of alpha-1,4 glucose, with alpha-1,6 branches 

        • 1 reducing end and many non-reducing ends 

    • absorb water - modified starches used for thickening agents 

    • made of glucose 

    • 1 reducing end but branches provide many non reducing ends (glycogen as well)

      • important for digestion of starches and how quickly they lead to changes in blood sugar (glycemic index) and for maintenance of blood glucose by the liver

        • amylose vs amylopectin (quinoa vs short grain white rice)

  • glycogen - storage form of glucose in the body, found in muscle and liver

    • branching chain of alpha-1,4 glucose with alpha-1,6 branches (but generally more branches than amylopectin)

    • 1 reducing end and many non-reducing ends 

    • liver 

      • helps maintain blood glucose (glycogen in liver can be mobilized and pushed out into circulation)

    • muscle

      • used for energy 

      • DOES NOT contribute to maintenance of blood glucose 

  • oligosaccharides

    • 3-10 monosaccharides

    • raffinose 

      • galactose-glucose-fructose

      • essentially sucrose plus galactose

    • starchyose

      • galactose-galactose-glucose-fructose

    • from legumes and role of microbiome

  • dietary fiber

  • cellulose - comes from minimally processed plant material 

    • purest form: cotton

    • indigestible for humans, but ruminants (cows) can digest 

    • insoluble fiber 

  • hemicellulose

    • complex structures 

    • soluble or insoluble, depending on type/structure

    • adds bulk to fecal material 

  • lignins - polycyclic alcohol

    • insoluble fiber and mostly non-digestible

    • comes from woody parts of plants 

    • provide bulk to fecal material 

    • do not need to know structure 

  • soluble fiber

    • pectins, gums, and mucilages

    • absorbs water (gel-like consistency)

    • softer, spongier parts of plants 

      • mucilages, seaweeds

    • used as food additives, thickeners, etc

  • grains

    • wheat kernel comprised of 

      • endosperm (83%)

        • starch, protein, and few fibres 

      • bran (14%)

      • germ (3%)

        • lipids, plant sterols, antioxidants, vitamin E, B, minerals, enzymes 

      • aleurone layer (6-9%) 

        • insoluble dietary fibres and few soluble fibres 

        • proteins, enzymes, phenolic compounds, lignans, vitamin E and B, minerals, phytic acid, lipids, plant sterols 

      • testa (1%)

        • alkylresorcinols, sterols, steryl ferulates 

      • outer pericarp

        • insoluble dietary fibres (xylans, cellulose, lignin)

        • antioxidants bound to cell walls (phenolic acids)

CARBOHYDRATES 3

• ~50% of that 100lb annual intake comes from processed foods

  • carbs that have been refined, concentrated and/or added to foods

  • potential link between high intake of sugar and fat storage 

• dental problems

  • added and natural sugars can contribute to tooth decay

  • oral bacteria ferment the sugars and produce acid that erodes tooth enamel 

• recommended dietary intake

  • simple sugars

    • limit to 10% of total energy

    • low nutrient density, high caloric density 

    • provides sweetness, texture, and color 

    • fermentation

  • carbs overall

    • 130 g/day for adults

    • starch not simple carbs

    • 45-60% of total energy 

      • 300g in a 2000 kcal dietary intake 

• healthy effects of dietary fiber

  • insoluble fiber

    • contributes to regularity by increasing fecal bulk and decreasing intestinal transit time 

    • too much fiber can BE BAD

      • proper hydration important for moving fiber through the body

      • over-intake can lead to intestinal blockages 

  • soluble fiber

    • slows gastric emptying

      • increases viscosity of stomach contents

    • possibly helps prevent obesity 

      • feel full for longer

    • diabetes

      • absorption of sugar is slowed, thus sharp spikes in blood glucose following a meal are minimized 

    • may lower blood cholesterol through 2 mechanisms

1. soluble fiber blocks enterohepatic circulation of bile acids

2. soluble fiber is metabolized into short-chain fatty acids that travel to the liver and reduce cholesterol synthesis 

• digestive tract path

  • food moves stomach -> small intestine -> large intestine at the cecum and moves up the right side of the body, across the abdomen near the stomach, and down the left side of the body 

• diverticulosis

  • lining of the intestines

    • epithelial lining with finger like projections known as mucosa

    • underneath is muscle tissue 

  • diverticula are little pouches of epithelial lining that pushes out in between the layers of muscle 

  • asymptomatic until revealed by a colonoscopy 

  • more common in elderly

• diverticulitis

  • rare complication of diverticulosis

  • material (bacteria) from small intestine becomes trapped in the diverticula 

    • can trigger inflammation and lead to internal bleeding because of the arrangement of small blood vessels in and around the smooth muscle tissue around the intestine 

  • treatment

    • rest the colon with soft diet (broth) or surgery may be needed 

• cancer

  • polyps and diverticula are not the same thing, structures are opposite 

  • polyps are outgrowths of the cells 

    • often harmless but can develop into cancer

  • dietary fiber

    • some evidence that fiber protects against colorectal cancers 

      • through the efficient dilution/binding/removal of any potential cancer-causing agent 

    • can promote healthy microbiome 

    • largely from observational studies

• enterohepatic circulation - portal vein

  • absorbed nutrients pass through the liver first 

    • carbs and proteins

    • fats are more complicated but still pass 

LIPIDS 1

• fatty acids

  • 4-24 C long

    • 16 and 18 most common in food

  • processed in 2-C units

  • methyl group (omega) at one end other end carboxylic acid (alpha)

  • saturation - refers to presence or absence of C=C

    • saturated fatty acids have no C=C

      • animal fats

    • Monounsaturated have a single C=C

      • olive oil

    • polyunsaturated have multiple C=C

      • seeds

• most polyunsaturated fats liquid at room temp

• saturated fats solid at room temp because they stack on top of each other

• saturated and unsaturated fats don’t stack the same since there is a bend at the C=C 

• essential fatty acids

  • we lack the enzymatic machinery to place C=C 

  • omega-6 and omega-3 must be from diet

  • deficiency

    • flaky skin, diarrhea, reduced healing, anemia, organ pace of cell turnover

• Eicosanoids - 20-C polyunsaturated

  • act as hormones, regulate blood pressure/clotting, immune/inflammatory response, GI secretions

  • generally act locally

  • many classes

    • linoleic acid (omega-6) - group 1 and 2

      • 1T per day plant oil

    • alpha linoleic acid (omega-3) - group 3

      • abuse may lead to hemorrhagic stroke

      • rich in fatty fish (salmon, tuna, sardines), canola or soybean oil

LIPIDS 2

• Rancidity - process of autoxidation/hydrolysis of fats/oils (air, light, moisture, bacteria)

  • produces short chain aldehydes, ketones, and fatty acids 

  • oxidation in lipids occurs at the unsaturations, more double bonds means more likely for this to occur

  • prevention

    • add antioxidants like Vitamin E, BHA, and BHT

    • hydrogenation or partial hydrogenation 

      • adding back H to unsaturated fatty acids 

      • altered structure can be useful

        • spreadable fats like imparting softer texture to butter (margarine) and shortening, used in baking 

• trans fat

  • most fatty acids with unsaturations are cis - the H are on the same side, and the chain is therefore kinked 

  • a small percentage are trans, H atoms on opposite sides 

    • chain is more linear and can behave more like a saturated fat 

  • consequences

    • raises LDL, promotes inflammation, promotes fat storage, stimulate cholesterol synthesis 

• triglycerides

  • storage form of lipids in our bodies 

  • most abundant form of lipids in our bodies 

  • glycerol head + 3 fatty acid chains 

    • three fatty acids attached to a glycerol form triglyceride and each one yields a water molecule 

  • do not cross cell membranes 

    • free FAs, monoglycerides, and glycerol can 

    • TGs must first be hydrolyzed (de-esterified) by a class of enzymes called lipases 

  • function

    • provide energy, energy storage, insulation/protection, transport of fat-soluble vitamins 

• phospholipids

  • contain 2 fatty acid chains with the third position linked to a phosphate group 

  • primary component of cellular membranes 

  • useful as emulsifiers due to amphiphilic nature 

  • emusifiers

    • phospholipids can organize in aq solution so that the hydrophilic head is oriented out towards water, with the interior becoming a hydrophobic core 

    • organization important for digestion of TGs

      • emulsified by bile acids during digestion

      • following TG hydrolysis, micelles are formed which are essential in lipid digestion 

• sterols

  • from cholesterol 

    • entirely from animal sources (don’t need to consume them)

    • important for cell membranes 

    • precursor to steroid hormones and fat-soluble vitamins 

      • corticosteroids, mineralocorticoids, estrogen, testosterone, Vitamin D, bile acids

• dietary cholesterol

  • liver makes it

    • 800-1500 mg per day

  • intake ~300mg per day

  • cholesterol can accumulate in the arterial walls and develop into atherosclerosis plaques 

LIPIDS 3

• lipoproteins - how lipids are moved throughout the body

  • phospholipid outer shells and TG interior that includes cholesterol

  • carries hydrophobic substance through aqueous system (blood)

  • chlyomicrons

    • transports diet derived lipids from small intestine to lymphatics then blood

    • least dense

• VLDL

  • created in liver from dietary and newly synthesized lipids

  • carries lipids and cholesterol to tissues

• LDL

  • bad cholesterol

  • derived from VLDL as cells remove TGs

  • mostly cholesterol

  • internalized by receptor pathway in liver and tissue

  • supplies cholesterol for growth and development of tissues

  • scavenged by white blood cells

    • attach to blood vessels and oxidize lipids (atherosclerosis)

• HDL

  • “good” cholesterol 

  • synthesized in liver and intestine

  • picks up cholesterol from dying cells and transfers to other lipoproteins and transport to liver for excretion

• lipoprotein lipase

  • enzyme attached to blood vessels that hydrolyze TGs, yielding glycerol and FFAs => delivers lipids to surround tissue

• adipose tissue

  • stores lipids and stored as TGs

• blood lipids profiles

  • measurements conducted after fasting

  • fed state

    • clearance of blood lipids

    • lipoprotein lipase is insulin sensitive and acts on chylomicrons and VLDL

    • lipids delivered to adipose and muscle

  • fasting state

    • hormone sensitive lipase activated in adipose tissue

    • TG breakdown and mobilization of glycerol and FFAs

    • FFA from adipose delivered to liver and muscle via albumin

• foam cells - when white blood cell tries to internalize a lot of cholesterol

  • stick to arterial walls can contribute to CVD

PROTEINS 1

• functions - enzymes, structural scaffolds, signaling (hormones), immune system (antibodies), transport, buffering (fluids/electrolytes and pH)

• source of Nitrogen

• Amino acids are amphoteric meaning they can carry a positive and negative charge 

  • L-isomers

• R-groups

  • basic - lysine, arginine, histidine

  • acidic - aspartate, glutamate

  • sulfur containing - cysteine, methionine

  • aliphatic - glycine, alanine, valine, leucine, isoleucine

  • hydroxyl - serine, therine, tyrosine

  • aromatic - phenylalanine, tyrosine, tryptophan

  • nitrogen containing - asparagine, glutamine

  • unique - proline

• essential aminos - Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

• non-essential aminos - Alanine, arginine, asparagine, aspartate, glutamate, glutamine, glycine, proline, serine

  • Conditionally dispensable - Cysteine, tyrosine, Phenylketonuria

• transamination

  • how we handle amino acids is strongly linked to the metabolism of Nitrogen

  • used to transfer nitrogen between amino acid backbones

  • used in synthesis of non-essential amino acids

• deamination

  • removal of amino group

  • ammonia is a problem

    • toxic and must be eliminated 

      • converted to urea in liver => to kidney => excreted in urine

  • keto acid

    • becomes fuel as glucose or fat

• polypeptides are ordered from the amino-terminal residue on the left to the carboxyl terminal residue on the right 

• denaturation - unfolding of a protein due to exposure to heat, alkali, acid, or salts

  • disrupts the secondary, tertiary, and quaternary structure 

  • makes proteins inactive and dysfunctional 

PROTEINS 2

• all or nothing rule - if an essential amino acid is deficient, you cannot make proteins that have that amino acid 

• RDA for protein

  • 0.8 g/kg healthy weight in adults

  • eq: intake = output

  • positive balance - intake > output (children, pregnancy)

  • negative balance - intake < output (fasting, disease states)

• Nitrogen Balance - 

  • 70 kg man needs ~56 g protein per day 

  • 55 kg women needs ~44 g/day

  • Nitrogen represents 16% of the weight of a protein 

  • equation: N balance = (protein intake (g) / 6.25g) - urinary urea N - (0.2 X urinary urea N) - 2g

• protein quality

  • limiting amino acid: an essential amino acid found in the shortest supply in a given protein source relative to the amounts needed for protein synthesis 

    • if any one essential amino acid is limiting, existing proteins must be dismantled to obtain it 

  • complete protein: contains all amino acids in sufficient quantities to support protein synthesis

    • animal proteins (meat, fish, eggs, and cheese) are complete

    • plant proteins likely incomplete 

      • soy protein is complete

  • complementary proteins: proteins obtained from two sources of food that make up for each other’s inadequate supply of essential amino acids 

• equations and values for protein

  • protein digestibility - a measure of the amount of amino acids absorbed from a given protein source

  • reference protein - a standard used to measure the quality of other proteins (egg protein)

  • biological value (BV) - amount of protein nitrogen retained for growth and maintenance expressed as a % of protein nitrogen digested and absorbed

• protein efficiency ratio is a determination of how well a given protein supports weight gain in growing rats over given period of time 

  • PER = weight gain (g) of rats on standard diet/amount of protein consumed

• chemical score - lowest ratio for any essential amino acid in a given protein source 

• protein digestibility corrected amino acid score (PDCAAS) - replaces PER evaluation for children over 1 year of age and non-pregnant adults 

  • used to correct for protein quality on food labels when expressed as % DV

  • PDCAAS - chemical score * digestibility of a protein 

    • chemical score [0 - 1]

    • digestibility [0.8 - 1]

    • protein lacking any essential amino = 0

• absorption

  • specific transporters in the small intestine help move individual amino acids into the intestinal cells 

  • amino acids that are not used by the intestinal cells are passed on to the liver 

DIGESTION 1

• digestive system

  • mouth

    • mucus, amylase, mastication

  • swallowing

    • voluntary movement of food from the mouth to the pharynx

    • reflex closes the epiglottis over the larynx

      • closes the trachea and allows food to move into the esophagus

  • esophagus

    • upper esophageal sphincter

    • peristalsis

    • lower esophageal sphincter => closes the distal end of the esophagus and blocks the reflux of stomach contents back into the esophagus

    • gastroesophageal reflux disease

      • lower esophageal sphincter is loose 

      • stomach contents reflux back into esophagus

      • not heartburn

      • treatment

        • neutralize acid, block acid secretion, proton pump inhibitor

  • stomach

    • extremely muscular organ

    • gastric secretions (HCl) cause acidification of the meal

      • denatures proteins and proteases enzymes 

      • pepsin secretion

        • unique protease that functions at low pH

        • begins to break up peptide bonds 

      • gastric lipase

        • can start hydrolyzing fatty acids 

      • intrinsic factor

        • vitamin B-12 absorption

    • muscle contractions grind and mix food to produce chyme

  • liver

    • produces bile acids that are stored in the gallbladder

    • central hub

  • pancreas

    • produces digestive enzymes

  • gastric emptying into small intestine

    • primary site of digestion and absorption

    • lumen

      • collectively called the mucosa

      • villi - small folds

        • rich blood supply

        • lined with a single layer of epithelial cells 

      • highly pleated

        • increased surface area 

        • increased interaction with food

        • compare with a smooth interior pipe 

      • crypt cells 

        • complex organization of cells as a result of the villi structure 

        • don’t project out in lumen

        • epithelial cell turnover every 3-5 days 

        • stem cells that replenish these epithelial cells are down at bottom of the crypt 

        • cells migrate from crypt up to the lumen

        • cell types

          • enterocytes - majority; digestion/absorption

          • goblet cells - secrete mucin

          • enteroendocrine cells - hormone secretion

          • paneth cells - immune monitoring 

    • receives digestive enzymes and bicarbonate from the exocrine pancreas 

    • receives bile acids from the liver via the gallbladder 

  • large intestine

    • large population of bacteria 

      • they digest dietary fiber and can produce short chain fatty acids that can be absorbed into the bloodstream 

    • water and some minerals are absorbed 

    • rectum - stores and expels feces 

    • transit of large intestine may take up to 3 days 

    • regularity

      • does not mean a particular time period 

        • everyone is different

        • frequency of bowel movements depends on microbiome, food, intake, genetics, etc

• control of GI function

  • autonomic nervous system

    • branch of nervous system that regulates function of visceral organs 

  • GI hormones

    • small polypeptides released from GI tract into blood

    • released in response to meals

    • travel to different regions of the digestive system to regulate GI function

    • secretion of various chemicals

      • digestive enzymes, mucus, water, bicarbonate, HCl, bile acids

    • regulation of GI motility

    • epithelial cell growth 

    • regulated to maintain homeostasis 

    • secretin and gastrin

• GI motility

  • peristalsis

    • sweeping motion that propels food forward 

    • swallowing, stomach, and some sections of small intestine

  • segmentation

    • closely spaced contractions in discrete areas of the intestine that act to mix the chyme with the digestive secretions and increase contact with the mucosal surface 

  • mass movement

    • contractions that occur over a large area of intestine that act to move the waste towards the rectum 

DIGESTION 2

• carb digestion

  • salivary amylase - begins to break down alpha-1,4 glycosidic bonds from amylose and amylopectin

    • does not break alpha-1,6 bonds

  • most carb digestion occurs in the small intestine

    • also uses amylase from the pancreas 

  • amylase converts amylose and amylopectin into dextrins 

    • dextrins further broken down by the brush border enzymes 

    • brush border

      • organization of microvilli on enterocytes looks like a fuzzy layer on a light microscope 

      • microvilli membrane is studded with glycosidases that break down the dextrin 

• carb absorption

  • lactose intolerance

    • do not produce lactase 

    • more frequent in asian, african, or mediterranean origin

  • only monosaccharides absorbed in the intestine 

    • glucose and galactose are actively transported by the Na+ dependent transport protein 

      • goes uphill against concentration gradients 

  • fructose transported by a separate GLUT5 transporter

    • facilitated transport - moves with concentration gradient

  • GLUT2

    • basal transporter that moves glucose, galactose, and fructose out of the cell and into the blood 

    • moves with the concentration gradient 

• protein digestion

  • stomach is where this largely starts 

  • HCl denatures proteins 

  • pepsin released

    • unique protease that is active at low pH

    • breaks apart proteins into pieces 

  • pancreas secretes digestive enzymes and bicarbonate into small intestine 

    • proteolytic enzymes are released from the pancreas as inactive proenzymes and are later activated in small intestine 

    • majority done in small intestine

  • enzymes hydrolyze peptide bonds producing oligopeptides 

• amino acid absorption

  • brush border peptidases hydrolyze oligopeptides into di and tripeptides and individual amino acids 

    • these are transported across the intestinal cell membrane by brush border transporters 

      • active and facilitated transport

    • further breakdown can occur inside cells

    • transporters move amino acids and small peptides out of basal region of cell and into the blood 

• lipid digestion

  • largely starts in stomach 

    • production of gastric lipase

      • hydrolyzes TG to FFA and monoglycerides 

  • small intestine is major site of fat digestion and absorption 

  • gallbladder stores and releases bile acids and lecithins 

    • bile acids and lecithins emulsify lipids, facilitate breakdown and transport 

• lipid absorption

  • Pancreatic lipase acts together with the protein co-lipase to hydrolyze TGs

  • Emulsification of fat droplets by lecithins and bile acids gives the co-lipase and lipase enzymes access to the TGs. End products are FFA, monoglycerides, and glycerol

  • Micelles form from monoglycerides and FFA surrounded by bile acids

    • Gives the lipids access to the epithelial cells (and is needed for lipid soluble vitamin absorption)

  • Absorption of FFA, monoglycerides, and glycerol is by diffusion and

  • protein mediated transport

  • Bile acids: produced in liver, released from the gallbladder, and most are

reabsorbed (~98%) in the terminal ileum and travel in the blood back to

the liver (enterohepatic circulation – via the hepatic portal vein)

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