Energy needs

 Energy is require for all basic physiological functions  Breathing  Digestion  Excretion  Muscle function  mobility  heart  Brain - most energy demanding  Active transport pumps (cellular level)

Energy needs: Energy needs: Units of measure of energy  Calories:  Traditional unit  One calorie of heat raised the temperature of 1g of water through 1°C  Other Units  1 kilocalorie = 1000 calories  Joules  SI unit  measure of energy exerted  1 calorie = 4.18 joules  1 kcal = 4.28 kJ

Energy needs: How Much Energy do we need  We need to provide, from our food enough energy to;  Provide for body functioning  Maintain our temperature  Sustain physical activity  No more, no less  If take in too little energy, the body uses reserves it has put by and we lose weight  If we take in too much energy, the body stores the excess food, usually as fat and we put on weight

 Food possesses energy  Energy is released when food is converted, ultimately into Carbon dioxide and water  Energy content depends on food consumed  Total energy available is a function of Quantity of food consumed Energy needs: Energy needs: Measurement of Energy Intake

 Different foods provide different amounts of energy for a given weight  Determined by composition of food  The following contribute to the energy content:  Carbohydrate  Fat  Protein  Alcohol Energy needs: Energy needs: Measurement of Energy Intake

 The following do not contribute to the energy content:  Vitamins  Mineral  Water  Various methods have been developed to determine the energy content of food Energy needs: Energy needs: Measurement of Energy Intake

 Bomb Calorimeter  Food is ignited electrically in the presence of oxygen  Heat of combustion is measured from a rise in water temperature  Heat of combustion represents the gross energy of the food  Energy lost during digestion and absorption  Affected by illness Energy needs: Energy needs: Measurement of Energy Intake

Bomb Calorimeter

 Proximate Principles  The amount of energy which the body receives from food is known as metabolised energy  Calculated from Proximate principles  These are standardised energy contents of food based on typical composition  Found from on food composition tables Energy needs: Energy needs: Measurement of Energy Intake

Metabolic Energy yields

Energy needs: Energy needs: Measurement of Energy Intake  100g of Potato crisps contain:  49.3 g of Carbohydrates  37.6g of Fat  5.6g of Protein  49.3 x 16 = kJ from Carbohydrate  37.6 x 37 = kJ from fat  5.6 x 17 =95.2 kJ from protein  Total kJ

Energy needs: Energy needs: Measurement of Energy Intake % Energy from carbohydrates, protein and fat

 Diet Surveys  Dietary and nutritional survey of British Adults (Gregory 1990)  Average UK dietary energy intake  Men 10.2 MJ  Women 7.02MJ Energy needs: Energy needs: Measurement of Energy Intake

Sources of energy in the British diet (adults) Energy needs: Energy needs: Measurement of Energy Intake

Energy Output Energy of food ATP + Heat Loss  50% efficiency ATP “Work” + Heat Loss  50% efficiency “Work” Heat Energy needs: Energy needs: Measurement of Energy Output

 Basal metabolic rate  Largest daily energy output  Definition: “the sum total of minimal activity of all tissue cells of the body under steady state conditions”  Osmotic pumps  Protein synthesis  Heart  Respiratory system  Digestive tract  Thermogenesis (Temperature maintenance)  Physical activity  Growth Energy needs: Energy needs: Components of Energy Output

 Body weight  Larger the body greater BMR  Lean body mass  Fat mass  Age  BMR highest in young infants  Falls with increase in age  2% per decade after age of 30  Decline in activity and proportion of lean tissue Energy needs: Energy needs: Basal Metabolic Rate

 Disease  Thyroid  Fever  Trauma  Stress  Drugs  increase  decrease  Undernutrition  Gender  Women 10% higher body fat than men  BMR lower for women  Pregnancy  Lactation  Other Factors  Genetics  Climate  Ethnicity

Energy needs: Energy needs: Basal Metabolic Rate W = body weight (kg)

BMR example  A woman 40 years old, weight 62kg  = (0.034 x 62)  = =  =5.7 MJ/day

 Physical Activity  Most control  Differing levels of activity  Energy expended relates to body size  Physical activity ratios (PARs)  Physical activity level (PALs ) Energy needs: Energy needs: Components of Energy Output

Energy needs: Energy needs: Physical Activity Ratios ActivityPAR Sleep1.0 Quiet sitting 1.2 Active sitting 1.6 Stationary standing 1.6 General Mixed (personal activities) 1.4 Activities requiring moving about 2.1 Walking2.8 Gardening3.7 Swimming4.8 Running6.0

Energy needs: Energy needs: Physical Activity Ratios  Bill is aged 40 and weighs 70kg  His BMR is calculate as follows:  (0.048 x 70) = 7.01MJ per day  Therefore:-  His hourly BMR =7.01/24 292kJ/hour

Energy needs: Energy needs: Physical Activity Ratios  He records his daily activity pattern  Sleeping 7hours  Driving 2hours  Personal activities 3 hours  Watching TV 3hours  Playing football 1 hour  At work sitting at desk 8 hours

Energy needs: Energy needs: Physical Activity Ratios - Example BMR/hr = 292 kJ/hr Total Energy use = 33.6 x 292 = 9811 kJ