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Energy & Metabolism

Energy & Metabolism. Energy derived from food we eat Released in chemical reactions (metabolism) Transferred into ATP Energy needed: Keep body alive Heart beating/ breathing/ maintaining temperature etc. BASAL METABOLIC RATE Activity Growth/ repair Reproduction. Energy balance.

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Energy & Metabolism

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  1. Energy & Metabolism • Energy derived from food we eat • Released in chemical reactions (metabolism) • Transferred into ATP • Energy needed: • Keep body alive • Heart beating/ breathing/ maintaining temperature etc. • BASAL METABOLIC RATE • Activity • Growth/ repair • Reproduction

  2. Energy balance • Simple Equation • Energy intake > Energy usage = Weight Gain • Energy intake < Energy usage = Weight Loss • Energy intake = Energy usage = No Weight Change Need to be able to measure energy intake, energy usage

  3. Energy measurement • Bomb calorimeter allows energy intake to be accurately determined

  4. Energy Measurement (Food) Carbohydrate 16 kJ.g-1 Fat 37 kJ.g-1 Protein 17 kJ.g-1 Alcohol 29 kJ.g-1 • Energy content of food • Measured in BOMB CALORIMETER • Well insulated box with a thermometer • Food is burned in pure oxygen • Heat given out determined from temperature rise • Energy content of food expressed in • kJ per gram N.B. 1lb (0.5kg) of body fat contains around 15000KJ (3500 calories)

  5. Stella 221 Baileys 129 Beer 182 Vodka 55 Aero Easter Egg 1109 Big Mac 492 Quarter Pounder 515 Calorie content of food

  6. Bomb calorimeter allows energy intake to be accurately determined • Energy usage – more difficult

  7. Direct Calorimetry • All energy used by the body ultimately is lost as heat • Measurement of heat production by a subject indicates the energy usage • Subject placed in a large insulated box • Heat exchanger (water flowing through pipes) allows measurement of temperature change in box • Very accurate • Very expensive and difficult

  8. Indirect Calorimetry • Majority of energy (ATP) used by body • from aerobic respiration. • Measure oxygen consumption • indicate energy usage by body • Inspired air 20.93% oxygen • Measure oxygen in expired air (16-18%) & volume of air expired over a given period of time • Calculate oxygen consumption • 1l oxygen provides approx. 20kJ energy • Calculate energy used over period of time

  9. Calculation • e.g. • 100l air expired over 10min • 21% O2 inspired air • 18% O2 expired air • Vol. O2 in inspired air = 21% of 100l = 21l • Vol. O2 in expired air= 18% of 100l = 18l • Vol. O2 used in 10 min =21-18l = 3l • Vol. O2 used per min = 0.3l • 1l O2 provides 20kJ energy • Energy expenditure = 20 x 0.3 = 6kJ.min-1

  10. Indirect Calorimetry • Still extremely accurate • Portable respirometers can be worn • Energy expenditure for various activities can be measured • Values for activities available in published tables • Energy usage diary can give good estimate of energy expenditure through a day

  11. Correlating HR and EE • Oxygen delivered by CV system • As Oxygen needs  HR  • Linear relationship between HR and O2 consumption • (fitness/activity varies slope) • Measure HR • Read oxygen consumption from graph • Portable HR monitor (wrist watch) • Inexpensive, easy, unobtrusive (no face mask, nose clips etc.)

  12. Energy needs 2218 kcal/day 1847 kcal/day 2754 kcal/day 2112 kcal/day 2536 kcal/day 1938 kcal/day

  13. Energy balance • Simple Equation • Energy intake > Energy usage = Weight Gain • Energy intake < Energy usage = Weight Loss • Energy intake = Energy usage = No Weight Change • Two ways to achieve energy balance • Reduce intake • Increase output • Easier to increase usage!!!!!!! • Extreme Calorie reduction diets NOT very good when only strategy used • Obesity on increase • Energy consumption decreasing in diet!

  14. Change in dietary mix required Dietary Energy Recommendations • Reduce FAT intake • Fat – energy dense • Reduce from 38% to 30% • Fat substitute - OLESTRA • Increase COMPLEX carbohydrate • Increase from 47% to 50% Food Standards Agency

  15. Changing Energy expenditure • Energy expenditure depends on: • Basal metabolic RATE • Thermic effect of FOOD • Physical Activity

  16. BASAL METABOLIC RATE • Regulated by: • Body Size • Bigger bodies bigger BMR • Body Composition • Lean tissue uses more energy than adipose (fatty) tissue • For a given weight a more muscular individual has a higher BMR than a fatter individual

  17. BASAL METABOLIC RATE • Regulated by: • Age • As age increases BMR decreases (2% per decade) • Sex • BMR higher in males • Females have more fat (25-30% c.f. 12-15%), • less metabolically active tissue

  18. BASAL METABOLIC RATE • Regulated by: • Nutritional Status • BMR decreases on a low energy intake • Loss of lean tissue reduces BMR • Survival adaptive mechanism • Typically BMR ~50cal per hour (200KJ.h-1)

  19. Thermic effect of Food • Digestion of food uses energy • Fats use 3% of their energy content • Carbohydrates use 9% of their energy content • Proteins use 17% of their energy content • For a high fat diet – most energy is made available to body • This energy is stored (fat) or has to be used • Reduce fat in diet, increase Carbohydrate & protein and get a double whammy • Protein/ CHO – 50% energy content per gram • Use up 17%/9% of their energy in digestion

  20. Pedal an exercise bike for 13 minutes. • Practice some fast dance steps for 16 minutes. • Work in the garden for 18 minutes. • Walk briskly for 22 minutes (3.5 mph). • Clean the house for 25 minutes • All use 100 calories (420KJ) Physical activity • Easiest of all • Energy needed for activity depends on: • Individual body size • (heavier more energy needed) • Type of activity • See table p34 • Intensity & duration • Squash uses 42kJ/min • Golf uses 16.7 kJ/min • Round GOLF uses more energy then 30 min squash • 3010 kJ c.f 1260 kJ

  21. Benefits of Exercise for Energy consumption/body composition • Energy expended in activity is used, not stored • Following exercise energy consumption remains elevated for some time • Post exercise oxygen consumption (EPOC) • 20-100kJ additional energy expended • Oxygen needed to replenish glycogen stores • Duration of EPOC is increased with more intense exercise • Exercise may increase BMR for a few days afterwards • Regular exercise is therefore important • Change in body composition • Lean tissue higher BMR than fatty

  22. Body Composition • Body mass • Poor indicator of patient health (prognosis) • Muscle (desirable – heavy), adipose (undesirable – light) • Better indicator is body composition • Useful to: • Assess health risk for patient • Monitor weight loss • Diseases/ dieting • Monitor training

  23. Estimating Body Composition • Body mass Index (BMI) • BMI=weight / (height)2 • Weight (kg), height (m) • e.g. • Weight = 101kg; Height = 1.82m • BMI=101/(1.82)2 • BMI=30.5 • Overwieght – 25.0-29.9 • Obese Class I – 30.0-34.9

  24. BMI • Easy, quick • Unreliable (for some people) • Large muscle bulk classified as obese because heavy, but still low fat • Unusual frame – very tall/ small misclassified

  25. Measuring Body Composition • Body consists of two parts • Fat mass (fatty tissues) • Fat free mass (muscles, bones, water etc.)

  26. DENSITOMETRY • Fat mass density= 1.1g/cm3 • Fat free mass density = 0.9g/cm3 • %fat = 495/density - 450 • Body density = body mass/ body volume • Body volume obtained by underwater weighing (Archimedes’ principle)

  27. Underwater weighing to obtain volume of body • Air expelled from lungs • Residual lung capacity (unexpired air volume calculated) • Body totally submerged, whilst sitting underwater on a seat suspended from a weigh machine – weight underwater (kg) • Difference between weight in air and weight underwater = weight of water displaced (Archimedes Principle) • Density of water = 1kg/l • Volume of water displaced (l) = weight of water displaced (kg) • Volume of water displaced = volume of body • Correct for residual lung capacity

  28. Calculation • 60kg person, weighs 2kg underwater • Volume of water displaced 58l • Density = 60/58 • 1.0345g/cm3 • %fat = 495/density – 450 • = 495/1.0345-450 • =28.5%

  29. Bod Pod • Air displacement method • Assess body volume by measuring volume of air displaced

  30. BOD POD Expensive Less distressing Very accurate UNDERWATER weighing Expensive Distressing Complex, difficult & time consuming Very accurate Comparison

  31. Skinfold Thickness • Widely used • Calipers used to measure thickness of skinfold (pinch skin + subcut. Fat) • 4 areas – triceps, subscapular, supra iliac, biceps • Sum calculated • Tables consulted to indicate % body fat • Quick, cheap, relatively easy (but practice required) • May not be accurate for unusual individuals • Difficult in very lean/ obese

  32. Bioelectrical Impedance Analysis • Fat is an insulator • Fat free mass is conductive • Electrical conductivity of body will indicate fat content • BIA – attach electrodes to feet/ hands • Measure conductivity • Easy (unskilled), quick • Affected by hydration level • Inaccurate in lean/ obese

  33. Waist/ hip ratio • Empirical observation that • Android (apple) – at risk of CHD, NIDDM (non-insulin dependent diabetes mellitus) • Gynoid (pear) – less risk of CHD, NIDDM • Measure waist/hipt circumference • Hips smaller than waist (android) • Suggests extra abdominal fat • Hips greater than waist (gynoid) • Waist at belly button: • Men 37-40in, Equivalent risk as BMI of 25-30; Over 40in, Equivalent risk as BMI >30 • Women 32-35in, >35in resp.

  34. OBESITY • Obesity = A chronic condition characterised by excessively high body fat in relation to lean tissue • BMI > 30kg/m2 • On the increase • Desirable 12-15% fat, male 20-30% fat, female 14% MEN 17% WOMEN 20% CHILDREN

  35. OBESITY – Health Risks • CHD – coronary heart disease • TYPE 2 (non- insulin dependent) diabetes mellitus • Cancers (colon, breast) • Bone & joint disorders • Respiratory problems

  36. OBESITY - Causes • Reduced physical activity • High, energy dense fat in diet • Genetic, metabolic & psychological factors also may play a part

  37. OBESITY – Treatment • Reduce energy intake • Or • Increase energy usage • Or • BOTH

  38. Recap – Benefits of Exercise for weight Control • Calorie reduction more successful if exercise included in weight control programme: • Exercise benefits: • Increased energy usage • More fatty tissue lost, (active) lean tissue augmented • BMR maintained (possibly increased), reducing calorie intake decreases BMR • Exercise need not be vigorous • Long duration, moderate intensity (brisk walk) • HEBS – 30min exercise over most days

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