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ENERGY VALUE OF FOODS. Submitted by, SELMA ABDUL SAMAD BCH-10-05-02 S3 MSc.BIOCHEMISTRY. The Energy Yielding Food Factors. Human body utilises potential energy in foods for maintaining life and doing work. The energy yielding food factors are Carbohydrates Proteins Fats

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  2. The Energy Yielding Food Factors • Human body utilises potential energy in foods for maintaining life and doing work. • The energy yielding food factors are • Carbohydrates • Proteins • Fats • In cells,enzymes degrade these by oxidation yielding energy • Carbs and fats give CO2 , water and heat while Proteins give urea along with these

  3. The energy value of Food • The energy or calorific value of food depends on the amount of energy yielding factors in them • This can be determined by oxidation in a bomb calorimeter • Units of energy include • CALORIE - one calorie expresses the quantity of heat needed to raise the temperature of 1 kg (1 L) of water 1°C (specifically, from 14.5 to 15.5°C). Kilogram calorie or kilocalorie (kcal) more accurately defines calorie.

  4. British thermal unit, or BTU - represents the quantity of heat necessary to raise the temperature of 1 lb (weight) of water 1°F from 63 to 64°F • The joule, or kilojoule (kJ), reflects the standard international (SI) unit for expressing food energy. To convert kilocalories to kilojoules, multiply the kilocalorie value by 4.184 • The following conversions apply: • 1 cal =4.184 J • 1 kcal = 1,000 cal = 4,184 J = 4.184 kJ • 1 BTU =778 ft-lb =252 cal =1,055 J • Mega joule = 1000 kJ = 239 kcal

  5. Humans need food energy to cover the basal metabolic rate; the metabolic response to food; the energy cost of physical activities; and accretion of new tissue during growth and pregnancy, as well as the production of milk during lactation. •  “Energy balance is achieved when input (or dietary energy intake) is equal to output (or energy expenditure), plus the energy cost of growth in childhood and pregnancy, or the energy cost to produce milk during lactation” (FAO, 2004).

  6. Overview of food energy flow through the body for maintenance of energy balance

  7. Metabolisable energy – Food energy available for heat production and body gains at nitrogen and energy balance • Net metabolisable energy - food energy available for body functions that require ATP. ie.,it is based on the ATP producing capacity of foods rather than total heat producing capacity.

  8. A large number of analytical methods for food analysis have been developed since the late nineteenth century, so have a variety of different energy conversion factors for foods. • The common ones are the Atwater System, Extensive General Factor System and Atwater Specific factor System. All of these are based on ME . • The energy values based on Atwater System are • 17 kJ/g (4.0 kcal/g) for protein • 37 kJ/g (9.0 kcal/g) for fat • 17 kJ/g (4.0 kcal/g) for carbohydrates • 29 kJ/g (7.0 kcal/g) for alcohols

  9. The Atwater specific factor system appears to be superior to the original Atwater general system, which took only protein, fat, total carbohydrate and alcohol into account. • There are other factors which are dependent on the NME and hybrid systems are also deviced with implications .

  10. Determination of Energy Value • Bomb Calorimeter • Measure the total or gross energy value of various food macronutrients • Bomb calorimeters operate on the principle of direct calorimetry, measuring the heat liberated as the food burns completely. • Heat of combustion refers to the heat liberated by oxidizing a specific food; it represents the food’s total energy value

  11. Bomb calorimetry is used to determine the enthalpy of combustion, DcombH, for hydrocarbons • Other calorimetries • Benedict’s oxy-calorimeter – measures the volume of oxygen required to burn a known weight of the food • Direct calorimetry – The relation between energy output and oxygen consumed has been determined using the human respiration calorimeter. Eg. Adult weighing 65 kgs Amount of heat output in 24 hours – 2400 kcal Amount of oxygen consumed in 24 hours – 500 litres Heat output per litre of oxygen consumed – 4.8 kcal

  12. Energy available – based on • Digestibility • Utilisability

  13. So the physiological energy value of foods vary from that seen in a bomb calorimeter. • In Bomb calorimeter,carbs and fats are completely oxidised to CO2 and water and protein with nitrogen too. But in human body this may not be effected • The veg. fibres are burnt in calorimeter while human body doesn’t actually utilise them for energy. • Also , in utilisation and digestion,certain percentage of each is lost and nitrogen is mainly excreted as urea..

  14. Loss in digestion – eg. In western countries, 2% for carbs, 5% for fats and 8% for proteins. • Loss of energy in metabolism due to Incomplete oxidation – no loss in case of carbs and fats. But for proteins,a part of the energy is lost as urea due to incomplete oxidation and is estimated as 1.2 cal per gram of protein oxidised. • Thus the Atwater-Bryant factors show the physiological energy values of foods.

  15. Nutrition label • Knowledge of nutritional value of foods is important • Many govt. has made it a rule to include nutrition labels in food packets

  16. RESPIRATORY QUOTIENT • Respiratory quotient – is the ratio between the volume of CO2 given out and the volume of O2 consumed by the human subjects. Respiratory quotient(R.Q) = Vol of CO2 producedVol of O2 consumed • When only carbohydrate is oxidised , RQ = 1For fats, RQ = 0.7For proteins , RQ = 0.82 • In the post absorptive stage of an average meal, with 10% protein, 20% fat and 70% carbs, RQ is about 0.82 • Respiratory Quotient is measured using Ganong’sRespirometer

  17. BASAL METABOLISM • It is the energy metabolism of a subject at complete physical and mental rest and having normal body temperature and in the post absorptive state.,ie.,12 hours after the intake of last meal • Basal metabolism can be measured using a Benedict-Roth apparatus. • Basal metabolic rate is thus he minimum amount of energy -- in the form of calories-- that your body requires to complete its normal functions, such as breathing, breaking down food, and keeping your heart and brain working. 

  18. RESTING METABOLIC RATE – It is the calories burned by the subject at rest. • It is synonymous with Resting Energy Expenditure or REE • BMR varies from person to person and increases with your amount of muscle tissue. Exercising increases your BMR, and it can stay raised after 30 minutes of moderate physical activity. • Though every individual has a slightly different rate, the average is about 70 calories per hour • BMR is measured under very restrictive circumstances when a person is awake, but at complete rest. An accurate BMR measurement requires that the person's sympathetic nervous system is not stimulated. RMR is measured under less strict conditions.

  19. BIOCHEMISTRY OF BMR • About 70% of a human's total energy expenditure is due to the basal life processes within the organs of the body • 20% of one's energy expenditure comes from physical activity and another 10% from thermogenesis, or digestion of food (postprandial thermogenesis)

  20. Measurement of BMR • BMR and RMR are measured by gas analysis through either direct or indirect calorimetry, though a rough estimation can be acquired through an equation using age, sex, height, and weight. • Also there are several formulas to calculate the approximate BMR of an individual • Dubois and Dubois found a formula to calculate the Body surface area of a human being A asA =W0.425 X H0.725 X 71.84where H is height in cmand W is weight in kg

  21. A standard table was plotted for BMR against age,sex and surface area in square meters. • Harris Benedict Formula •  takes the number produced by the BMR formula and multiplies it depending on your activity level • Basal Metabolic Rate (BMR) Formula takes several variables like height, weight, age and gender to calculate your calorie needs as if you did not do any exercise

  22. English BMR Formula Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age)Men:BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) - ( 6.8 x age) Metric BMR FormulaWomen:BMR = 655 + ( 9.6 x weight in kilos ) + ( 1.8 x height in cm ) - ( 4.7 x age )Men:BMR = 66 + ( 13.7 x weight in kilos ) + ( 5 x height in cm ) - ( 6.8 x age)

  23. The BMR formula uses the variables of height, weight, age and gender to calculate the Basal Metabolic Rate (BMR). This is more accurate than calculating calorie needs based on body weight alone. The only factor it omits is lean body mass and thus the ratio of muscle-to-fat a body has. •  Leaner bodies need more calories than less leaner ones. Therefore, this equation will be very accurate in all but the very muscular (will underestimate calorie needs) and the very fat (will over-estimate calorie needs).

  24. Mifflin equation • For menBMR = (10 x weight in kg) + (6.25 x height in cm) - (5.0 x age in years) + 5 • For womenBMR = (10 x weight in kg) + (6.25 x height in cm) - (5.0 x age in years – 161 • Katch-McArdle Formula • The Katch-McArdle Formula is a basal metabolic rate calculation that you can use when you know your lean body mass measurement. As a result, it's a more accurate metabolism formula than Harris-Benedict Formula. • Because it uses your lean body mass measurement, there is no reason for separate formulas for men and women in the Katch-McArdle Formula.

  25. The formula is BMR = 370 + (21.6 x lean body mass in kg) • Cunningham Resting Metabolic Rate Calculation • RMR = 500 + (22 x lean body mass in kg) • This calculates the RMR

  26. Factors Affecting Basal Metabolic Rate • Gender: Men have a greater muscle mass and a lower body fat percentage. Men therefore have a higher BMR. • Genes: Some individuals are born with a fast metabolism others with a slower metabolism. • Age: BMR reduces, as one gets older. After 20 years, it drops by 2 per cent per decade. • Exercise: Exercise helps raise your BMR by building extra lean tissue. Lean tissue is more metabolically demanding than fat tissue. • Weight: The heavier you are, the higher your BMR.

  27. Body Surface Area: A tall thin person will have a higher BMR than a shorter, fatter person. BMR also increases in pregnant women. • Body Fat Percentage: The more lean tissue on the body, the higher the BMR, the more fatty body tissue, the lower the BMR. Men generally have a 10-15% faster BMR than women. • Diet: Starvation or serious abrupt calorie-reduction can dramatically reduce BMR by up to 30 percent. Restrictive low-calorie weight loss diets can cause your BMR to drop as much as 20%.

  28.  Food Types - The type of food we eat can also have a significant effect on our basal metabolic rate.Notably, protein rich foods have the greatest effect with carbohydrates and fats eliciting a smaller impact. High-fat foods and refined sugars, however, can reduce BMR since they are lower in fiber and bulk.Getting the proper amount of vitamins and minerals can help regulate BMR to keep that process efficient.

  29.  Hormones - In terms of BMR, the most influential hormone is called Thyroxin, which is produced by the Thyroid Gland. One function of Thyroxin is to regulate BMR. Higher levels of Thyroxin lead to a greater BMR.Thyroxin release can be affected negatively through extreme dieting.Testosterone/sex hormone promotes BMR. Estrogen also increases BMR,but less in compare to testosterone because of less metabolic activity in females.Cortisol is the only hormone showing both catabolic activity as in fever it increases BMR as temprature increases, and anabolic activity as in sleep it decreases BMR upto 10-15%. Growth hormone also increases BMR.

  30.  Muscle Mass - Muscle is an active tissue in so much as it needs energy to live. The more muscle a person has, the greater the demand for energy, and the higher the BMR.

  31. The more muscle fiber, the higher your BMI as muscle, even at rest, burns significantly more calories than fat and other tissues. This is the reason that strength training is so important to a weight loss program. Aerobics and cardio exercises are good to a point, but if overdone can actually break down muscle tissues for energy which can be counter-productive to weight loss. An efficient exercise program will include both cardio and strength training.

  32. Heredity - hereditary factors,can influence basal metabolism. We all know of people who seem to eat voraciously but never seem to gain weight, and others eating normal amounts gain weight easily. Some people have what can be called a thrifty metabolism—that is, they conserve more energy than the average person, so it is much easier for them to gain weight. A child with no obese parents has only a 10% risk of becoming obese; a child with one obese parent has a 40% risk, and with two obese parents, 80%.

  33. Temporary factors affecting BMR include: • Fever: Fevers raises the BMR • Stress: Stress hormones also raise the BMRIn times of stress the hormones Adrenaline and Noradrenaline are released, which have the effect of increasing cellular metabolism. • Temperature: Both the heat and cold raise the BMR.As our body temperature increases, the rate at which our bodies use energy increases. Indeed a 1% increase in body temperature can elicit an increase in BMR in the region of 10% (Tortora and Grabowski 1993) •  Sleep : During sleep BMR falls by 10% below that of levels measured when person is awake.

  34.  Climatic Conditions : People living in cold climate have higher BMR compare to people living hot climate • Caffeine and tobacco use: can increase metabolic activity. • Certain medications, such as anti-depressants can modify the BMR, leading to weight gain • After an injury, BMR can increase (temporarily) while the body uses EFAs and proteins to rebuild damaged structures and create new tissue

  35. ENERGY METABOLISM DURING WORK • Energy requirement is the amount of food energy needed to balance energy expenditure in order to maintain body size, body composition and a level of necessary and desirable physical activity consistent with long-term good health. This includes the energy needed for the optimal growth and development of children, for the deposition of tissues during pregnancy, and for the secretion of milk during lactation consistent with the good health of mother and child.

  36. Daily Requirement • Recommended Daily Intake • Heart rate monitoring (HRM): A method to measure the daily energy expenditure of free-living individuals, based on the relationship of heart rate and oxygen consumption and on minute-by-minute monitoring of heart rate. • Total energy expenditure (TEE): The energy spent, on average, in a 24-hour period by an individual or a group of individuals. By definition, it reflects the average amount of energy spent in a typical day, but it is not the exact amount of energy spent each and every day.

  37. Physical activity level (PAL): TEE for 24 hours expressed as a multiple of BMR, and calculated as TEE/BMR for 24 hours. In adult men and non-pregnant, non-lactating women, BMR times PAL is equal to TEE or the daily energy requirement. • Physical activity ratio (PAR): The energy cost of an activity per unit of time (usually a minute or an hour) expressed as a multiple of BMR. It is calculated as energy spent in an activity/BMR, for the selected time unit

  38. What actually Happens ……. • Why can’t we sprint forever ?? Work & Muscle energy Relation • These data are from the 1964 Olympic competitions.  Running speed is plotted against the duration of the race. Competitors running more than 30-40 seconds reduced their velocity markedly and a continual and gradual decrease occurred after about 2 minutes.  Marathon runners ran approximately half as fast as sprinters.   • The explanation for this phenomena is that differing energy sources are used by working muscles, the choice being related to the rate of usage.  Stored high-energy phosphates energy (ATP-ADP and phosphocreatine) give the most rapid regeneration of utilized ATP.

  39.  A 100 meter sprint takes less than 10 seconds .  During this very short period the driving force is stored high-energy phosphate.  The runners can perform almost without breathing, using energy stored as ATP or creatine phosphate (~P) or glycogen in the active muscles.  In contrast to long-distance runners, sprinters are often large, very muscular people.  They are "specially equipped"  for explosive function for very short periods. • The energy supply for those who run from about 60 seconds to three minutes is also stored energy, but in this case it is primarily glycogen stored in muscles (and blood glucose) that provides energy.  Glycogen must be oxidized to pyruvate, lactate and CO2 to provide the ATP required for muscle activity. 

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