1 / 12

Lecture 7

Lecture 7. Energy Balance and Carbohydrate Metabolism. Indirect Calorimetry. Measure rate of O 2 consumption since fuel oxidation requires O 2 Assume that energy released when O 2 is used = 20.2 J/ml (for fat, CHO, protein)

lgulley
Download Presentation

Lecture 7

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 7 Energy Balance and Carbohydrate Metabolism

  2. Indirect Calorimetry • Measure rate of O2 consumption • since fuel oxidation requires O2 • Assume that energy released when O2 is used = 20.2 J/ml (for fat, CHO, protein) • Ratio of O2:CO2 gives an indication of which type of fuel is burning: • The respiratory quotient • RQ for carbs: 1 • RQ for fat: ~0.7 • Can also tell us if someone is making fat • RQ > 1

  3. Doubly Labelled Water • Subject consumes 2H218O (D218O) • Like normal H2O This reacts with CO2 produced in fuel oxidation to form H2CO3 • All the oxygen atoms in H2CO3 are equivalent, so during the reverse reaction, some oxygen goes into CO2 and will be lost at the lungs. • The rate of 18O loss could then be used to guage how much CO2 was produced • And hence the rate of fuel oxidation • Since oxygen could also be lost through water excretion, we need the 2D to indicate depletion through excretion, sweating, etc • The difference indicates the true rate of carbon dioxide production. • Very good for long term assessment • But expensive and needs specialised equipment (mass spectrometer!)

  4. Regulation of Food Intake • Controlled by many hormones and neuropeptides (see Frayn Ch 11) • Leptin • Adipostat or Lipostat • Communicates size of fat stores to the brain • Secretion of leptin is proportion to the amount of fat stored in white adipose tissue • Leptin binding to receptors in the hypothalamus elicits satiety • Mice without leptin are hyperphagic, i.e. eat without control • when leptin is injected to these mice: •  food intake •  energy expenditure in brown adipose tissue • People without leptin are hyperphagic • ..and they respond to leptin injections • So could leptin injections be the ‘cure’ for obesity?

  5. No! • Obese people have higher blood [leptin] • More and bigger WAT cells • So extra leptin does not help • Indeed, they may be leptin-resistant • Also humans have a small amount of brown adipose tissue (ie, can’t respond to the leptin by increasing EE) • A lack of leptin may tells us to start eating, rather than a excess of leptin telling us to stop eating

  6. Carbohydrates • General formula –C(H2O)– • i.e. all carbon atoms are hydrated • Carbohydrates exist in 3 forms • Monosaccharides • disaccharides – dimers of monosaccharides • Polysaccharides – polymers of monosaccharides • Starch is the most common source of dietary carbohydrates • Some from disaccharides, • sucrose (glucose + fructose) from sugar • lactose (glucose + galactose) from milk/dairy • a little comes from monosaccharides • Fructose from fruit and honey • Glucose from lollies!

  7. Disaccharide Digestion • Disaccharides need to be split into monosaccharides prior to absorbtion • Lactose • Needs lactase (beta-galactosidase!) • Lack of lactase will result in lactose intolerance, i.e. lactose will pass through the small intestine undigested, and undigested lactose will be fermented by the bacteria in the large intestine  produces organic acids and gases  causes irritation • Lactose intolerance is related to ethnic background • 3% Danes lactose intolerant but >90% Thais intolerant • Sucrose • Digested by sucrase • Rarely deficient • Used in the confectionary industry to get soft centres

  8. Starch • 2 types • Amylose • Amylopectin • Digested by amylase • Digestion starts in the mouth - saliva contains amylase • Most digestion occurs in the small intestine • Most of the starch will be digested and absorbed in the small intestine

  9. Amylose • Glucose molecules are joined end-to-end • Is a straight, linear molecule • Can form sheets and helices which stack on top of each other - these structures are difficult for enzyme to penetrate,  hard to digest • Some amylose will end up in the large intestine undigested, which will be fermented by bacteria  produce short chain volatile fatty acids and gases • Examples of food contains amylose are legumes, pulses and old world strains of wheat, barley and rice.

  10. Amylose • Glucose molecules are joined by a14 glycosidic bonds, i.e. C1 on a glucose molecule is joining C4 on the other glucose molecule

  11. Amylopectin • Easy to digest • Highly branched • At branch points, glucose molecules are joined by a16 glycosidic bonds • Branching occurs about every 20 residues

  12. Euglycemia • Importance of keeping blood [glucose] at 5 mM • Hypoglycemia • [glucose] < 2 mM leads to coma • Brain has obligatory requirement for glucose • Hyperglycemia • Glucose is a reactive molecule • Glycosyates proteins • Reaction with amine residues • The greater the glycemia and the longer the exposure, the more the glycoslation • Glycosylated proteins tend to be dysfunctional • Problem particularly affects tissues in direct contact with blood • Kidneys – nephropathy • Retina – retinopathy • Blood vessels – endothelial cells – vascular disease • After a carbohydrate meal, priority is to dispose of glucose • Uptake into tissus, conversion into glycogen, fat or carbon dioxide • Liver has first look at the glucose • Direct contact to gut via hepatic portal vein • Hyperglycemia ellicits insulin secretion • Insulin will stimulate glucose uptake and storage/oxidation of glucose

More Related