Energy Metabolism Energy derived from food we

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

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

Energy measurement n Bomb calorimeter allows energy intake to be accurately determined

Energy Measurement (Food) Carbohydrateof food 16 k. J. g-1 n Energy content n Fat. Measured in BOMB CALORIMETER -1 37 k. J. g n Well insulated box with a thermometer n Food is Protein burned in pure oxygen -1 17 k. J. g Heat given out determined from temperature rise 29 k. J. g-1 Alcohol n Energy content of food expressed in n – k. J per gram N. B. 1 lb (0. 5 kg) of body fat contains around 15000 KJ (3500 calories)

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

n Bomb calorimeter allows energy intake to be accurately determined n Energy usage – more difficult

Direct Calorimetry All energy used by the body ultimately is lost as heat n Measurement of heat production by a subject indicates the energy usage n n n 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

Indirect Calorimetry n Majority of energy (ATP) used by body n n from aerobic respiration. Measure oxygen consumption n indicate energy usage by body n n n 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 1 l oxygen provides approx. 20 k. J energy Calculate energy used over period of time

Calculation n e. g. n n n n n 100 l air expired over 10 min 21% O 2 inspired air 18% O 2 expired air Vol. O 2 in inspired air = 21% of 100 l = 21 l Vol. O 2 in expired air= 18% of 100 l = 18 l Vol. O 2 used in 10 min =21 -18 l = 3 l Vol. O 2 used per min = 0. 3 l 1 l O 2 provides 20 k. J energy Energy expenditure = 20 x 0. 3 = 6 k. J. min-1

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

Correlating HR and EE n Oxygen delivered by CV system n n Linear relationship between HR and O 2 consumption n n (fitness/activity varies slope) Measure HR n n n As Oxygen needs HR Read oxygen consumption from graph Portable HR monitor (wrist watch) Inexpensive, easy, unobtrusive (no face mask, nose clips etc. )

Energy needs Age (yrs) Est. Average Energy needs (male) 11 -14 9. 27 MJ/day Estimated average energy needs (female) 7. 72 MJ/day 15 -18 8. 83 Mj/day 2218 kcal/day 11. 51 MJ/day 2754 kcal/day 19 -50 10. 60 MJ/day 2536 kcal/day 1847 kcal/day 2112 kcal/day 8. 10 MJ/day 1938 kcal/day

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

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

Changing Energy expenditure n Energy expenditure depends on: Basal metabolic RATE n Thermic effect of FOOD n Physical Activity n

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

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

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

Thermic effect of Food n Digestion of food uses energy n n n 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 n This energy is stored (fat) or has to be used n n Reduce fat in diet, increase Carbohydrate & protein and get a double whammy n n Protein/ CHO – 50% energy content per gram Use up 17%/9% of their energy in digestion

Physical activity • Pedal an exercise bike for 13 minutes. n Easiest of all • Practice some fast danceactivityfor 16 minutes. n Energy needed for steps depends on: n Individual • Work in the gardenbody size for 18 minutes. – (heavier more energy needed) • Walk briskly for 22 minutes (3. 5 mph). n Type of activity – See table p 34 • Clean the house for duration 25 minutes n Intensity & duration • All use – Squash uses 42 k. J/min 100 calories (420 KJ) – Golf uses 16. 7 k. J/min n Round GOLF uses more energy then 30 min squash – 3010 k. J c. f 1260 k. J

Benefits of Exercise for Energy consumption/body composition Energy expended in activity is used, not stored n Following exercise energy consumption remains elevated for some time n n n 20 -100 k. J 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 n n Post exercise oxygen consumption (EPOC) Regular exercise is therefore important Change in body composition n Lean tissue higher BMR than fatty

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

Estimating Body Composition n Body mass Index (BMI) n BMI=weight / (height)2 n Weight (kg), height (m) e. g. n Weight = 101 kg; Height = 1. 82 m n n n BMI=101/(1. 82)2 BMI=30. 5 n n Overwieght – 25. 0 -29. 9 Obese Class I – 30. 0 -34. 9

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

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

DENSITOMETRY n Fat mass density= 1. 1 g/cm 3 n Fat free mass density = 0. 9 g/cm 3 n %fat = 495/density - 450 n Body density = body mass/ body volume n Body volume obtained by underwater weighing (Archimedes’ principle)

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

Calculation n 60 kg person, weighs 2 kg underwater Volume of water displaced 58 l n Density = 60/58 n 1. 0345 g/cm 3 n n %fat n n = 495/density – 450 = 495/1. 0345 -450 =28. 5%

Bod Pod n Air displacement method n Assess body volume by measuring volume of air displaced

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

Skinfold Thickness n Widely used n n n n 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

Bioelectrical Impedance Analysis Fat is an insulator n Fat free mass is conductive n n n n 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

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

OBESITY n Obesity = A chronic condition characterised 14% MEN by excessively high body fat in relation to lean tissue 17% WOMEN n BMI > 30 kg/m 2 n On the increase 20% CHILDREN n Desirable 12 -15% fat, male 20 -30% fat, female

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

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

OBESITY – Treatment n Reduce energy intake n n Increase energy usage n n Or Or BOTH

Recap – Benefits of Exercise for weight Control Calorie reduction more successful if exercise included in weight control programme: n Exercise benefits: n n 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 n Long duration, moderate intensity (brisk walk) n HEBS – 30 min exercise over most days n