Week 3 Carbohydrates Flashcards
Liver: Metabolism Mediator
> Detoxification > AA + FA metabolism > Urea Cycle > Gluconeogenesis > Glycogen synthesis/store > Alcohol metabolism > Bile, cholesterol, lipid and blood protein synthesis
Imperatives of Metabolism
- ATP production (even during fasting)
- Maintain blood glucose (5 mM for brain function)
- Sources: carbs, FA, AA
- Absorption: 1-3 hours after meal (post prandial)
- Post-Absorption: FA
Pancreas: Insulin and Glucagon
- Alpha Cells: secrete glucagon
> Raises BGL –> Increases breakdown/ glucose synthesis
> + Epinephrine Increases lipolysis/HSL –> decreases fat storage/ Increases release - Beta Cells: produce insulin (most abundant of islet cells)
> Lowers BGL –> increases storage/ glycogen synthesis
> Decreases lipolysis/HSL –> Increases fat storage
Archibald Garrod: Inborn errors of Metabolism
Investigation of alkaptonuria
> Single enzyme error and Mendelian inheritance
> Disease: intermediate of aromatic AA metabolism in urine (homogentisic acid buildup)
Asbjorn Folling:
Phenylketouria (PKU)
Molecule in urine had an entity that reacted to iron (ketone with aromatic residue)
> PKU deficient: NO L-phenylalanine –> L-tyrosine via phenylalanine hydroxylase (PAH blocked)
> Transamination of phenylalanine –> phenylpyruvate via alpha-keto –> glutamate (PHENYLPYRUVATE BUILDUP –> TOXIC)
> Diet solution: limit phenylalanine (NO ASPARTAME); provide essential tyrosine
Carbohydrates
- Mono: fructose, glucose, galactose
> Same structure; either aldehyde/ketones
> Anomer rings: circular formation due to OH attacking aldehyde group –> hemi-acetal –> alpha and beta forms (linear and ring form oscillating) - Di-: maltose (Glu+Glu), sucrose (Glu+Fruc), Lactose (Glu+Gal)
> Maltose: alpha 1-4 glycosydic
> Sucrose: alpha 1-6
> Lactose: beta 1-4
**Raffinose: Gal a1-6 Glu a1-4 Fruc (humans have no alpha-galactosidase –> gut bacteria act up)
**Beano: enzyme-based dietary supplement to reduce gas (has a-GAL and invertase) - Poly: starch (straight chain amylose/ branched amylopectin), glycogen (muscle and liver), fibers (soluble pectin/ insoluble cellulose)
> Digestible: a1-4 (starch and glycogen; some a1-6; both have glucose monomers)
> Undigestible: b1-4 (cellulose made from beta-cellulose monomers)
Glycogen
Short term storage supply of glucose
> Human: 450g or enough for 1.5 days (Liver 100g, muscle 400g, brain very little)
>**Liver glycogen: blood-releasable glucose
> **Muscle glycogen: intracellular glucose ONLY
Fibers (not digested by human enzymes)
- Soluble: pectins, gums, mucilage
> Dissolves in water –> bacteria fermented in colon to organic acids (butyric: signals to GI track and body) - Insoluble: cellulose and hemicellulose
> No water dissolving thus poor fermentation
Carbs Digestion Overview
- Amylase: starch –> maltose
- Amylase inactivated by strong acid
- Amylase from pancreas: starch –> maltose
- SI enzymes: disac –> monosac
- Absorbed monosac into blood –> liver
- Soluble fiber fermented into acid/gases by LI bacteria
- Insoluble fiber in feces; very little carb present
SI glucose absorption: Na+ Glucose Cotransport
- Apical surface SGLT1 (Sodium Glucose Transporter)
- Basal Surface GLUT2 (uniport glucose transport via faciliated diffusion)
* Muscle absorption of glucose is by ACTION OF INSULIN REGULATED GLUT4 ONLY**
Carbohydrates are Useful Because…
- Support glycogen reserves in muscles and livers
> Glycogen amount increases over work time
> Glucose for brain comes from liver glycogen usually
> Low glycogen: AA +
glycerols –> glucose produced - Protect against ketosis and protein loss
> KETOSIS: Glycogen storage drops and BGL starts dropping –> glucogenesis/glucogenenic AA/Krebs intermediates/FA oxidation powering make glucose –> Acetyl-CoA buildup and ketone bodies form - Provide fibers
Starvation Progression
- Glycogen gone (24 hrs)
- Fat/protein gone (3-4 days)
- Slow protein degradation –> lipids become primary fuel –> brain uses ketone bodies
- WORST CASE: (prolonged)
> AA –> TCA intermediates to make glucose (lipids power liver; ketosis high muscle wasting)
Diet: Carb requirements
- At least 50-100g/d carbs
- RDA = 130 g/day for adults
- Average consumption is 180-330 g/day in US
Diverticula/Diverticulosus
Pockets form in walls of digestive tract
> Inner layer of intestine pushes through weak spots in outer lining –> pouches bulge out in colon
> 50% of 60+ y.o. have this condition
> Fibers: Increase bulk/soften stools; Less elimination pressure/constipation/piles/diverticula
Soluble Fibers + Microbes
- Binds Glucose –> slow glucose absorption –> lower diabetes risk
- Binds cholesterol/biles –> slow abs –> lower CVD risks
- Reduce appetites –> lower obesity risks
- Feeds colon microbes (fermentation) –> GI track lining and IS nourished –> lower asthma, Crohn’s and inflammation risks
Meta-Analysis
Quantitative epidemiological study design
> Assess previous research studies to derive conclusions about topic
> Benefits: consolidated review of a large and potentially conflicting body of literature; more precise estimate of treatment effect/risk factor of disease
Aune Study: Dietary Fiber and Breast CA risk
Case-Control –> dietary fibers are inversely related to Breast CA risk, but only observed among studies with a large range (13+ g/day) or high level of intake (25+ g/day)
Microbial Metabolism of Fibers influence asthma/hematopoiesis
- Mouse model shows high-fiber diet reduces (Stained) mucus accumulation in lungs
> Low fiber diet (89% Firmicutes, low Bacteroidetes) increase risks
> High fiber diet with pectin (52% Firmicutes and 42% bacteroidetes) decrease risks
> Increase SCFA too to stimulate growth of bifidobacterium and bacteroidetes
RDA : Fibers
- Women: 25g/day
- Men: 38g/day
- US avg: 14-17g/day
> Sources: whole plant-based foods; vegetables, beans, whole grains
Hyperglycemia
125 + mg/dL
> Excessive thirst, hunger and urination (kidney filters and releases glucose in urine –> dehydration)
> Glucagon: increases glycogen breakdown + glucose synthesis (alpha cells)
Hypoglycemia
50 - mg/dL
> Nervous, irritability, headache (no fuel)
> Insulin: Increases glucose breakdown and glycogen synthesis (Beta cells)
Glycemic Index (GI) and Glycemic Load (GL)
- Changes in BGL caused by 50g of carbs (compared to 50g of glucose)
> (BGtest/BGgluc)x100
> 8-10 fasted subjects with 50g carbs monitored for 2-3 hours
> 55- low (Spaghetti), 55-70 intermediate (New potato), 70+ high (White rice) - (GI/100) x g of carbs
> 15- low (Carrots), 15-20 intermediate (New potato), 20+ high (Baked beans)
> High problems: 1. easily hungry (obesity); 2. risk for CHD (women); 3. risk of insulin insensitivity
Insulin and Diabetes: Banting and Best
- Pancreas removal caused diabetes in dogs
- B&B: insulin was destroyed by hypothesized enzymes
> Tie off pancreatic duct –> protease secreting cell death –> extract pancreas and stabilize BG
> Active signal purified was insulin
Type I Diabetes
5-10% (juvenile onset)
> Autoimmune loss of beta cells –> insulin-dependent
> Treatment: insulin injection
> Fatality: BGL 40 - mg/dL
