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Basal Metabolic Rate (BMR)

Basal Metabolic Rate (BMR). Basal Metabolic Rate. Sustain vital functions like those of heart, circulation brain, lungs and cellular functions. OR It is the minimum amount of energy required to maintain life, OR

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Basal Metabolic Rate (BMR)

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  1. Basal Metabolic Rate(BMR)

  2. Basal Metabolic Rate Sustain vital functions like those of heart, circulation brain, lungs and cellular functions. OR It is the minimum amount of energy required to maintain life, OR Energy required by an awake person during physical, emotional and digestive rest. BMR of a sleeping person is lower than awake person.

  3. Normal BMR Adult men =34-37 kcal/hr/Sq m Adult women = 30-35 kcal/hr/Sq m For day to day calculation Males = 24 kcal/kg body wt/day • According to International Commission on Met. Rate the BMR of SE Asian people is a little lower than European

  4. Determination of BMR by Read’s Formula % BMR Change = 0.75 (PR +0.74 x PP)– 72 • PR = Pulse rate • PP = Pulse pressure • It gives BMR correct within ± 10% of the normal

  5. EXAMPLE Systolic BP =130 mm Hg Diastolic BP=90 mm Hg Pulse Rate =74/minute Pulse pressure=130-90=40 mm Hg 0.75(74+0.74x40)-72 0.75(103.6)-72 =77.7-72 =+5.7 % This value is % BMR change

  6. Basal Metabolism • Energy requirement varies with PAL & environmental conditions • Energy production is more Or less the same under standard condition known as “Basal Metabolism” • Conditions: • Awake but complete rest – Physical / mental • Fasting at least 12 –18 hours – (Post absorption state)

  7. Basal Metabolism Postabsorptive state allowed to avoid • Effect of digestion and absorption • Effect of SDA of food stuff • Prevent any chance of starvation 3. Recumbent / reclining position 4. Remain in normal living condition • Temperature, Pressure & Humidity

  8. Basal Metabolism • Under these conditions the energy expenditure is only on: • Respiration • Circulation • Muscle tone (skeletal and smooth muscles) • Functions of viscera (kidney, liver & Brain)

  9. Amount of heat given off by a subject who though awake is lying in a state of maximum physical and mental rest under comfortable condition of temperature , pressure ,humidity and 12-18 hours post-absorptive state.

  10. Significance of BMR It helps in the calculation of daily energy requirement of a person. It helps in planning diet for an individual. It also helps in the differential diagnosis of leukemias , polycythemia , addison’s disease. BMR helps in the assessment of thyroid function.

  11. Factors Affecting BMR

  12. The rate of metabolism at "basal" conditions has been found to vary in different individuals due to different factors.

  13. Age • In period of active growth BMR is high. • The BMR of children is much higher than adults • Reaches maximum by 5 years • Is low in old age • Roughly speaking it is inversely proportional to the age

  14. BMR Variation with Age

  15. Sex • Women normally have a lower BMR than men. • BMR of females decline between the ages of 5 and 17 more rapidly than those of males.

  16. Environmental Temperature • Incold climate BMR is a compensatory mechanism to maintain body temperature

  17. Fever • BMR is high in febrile state • 12% rise is found associated with 1oC rise in temp

  18. Racial variations When the BMR of different racial groups is compared, certain variations are noted • BMR of adult Chinese is equal to or below the lower limit of normal for westerns. • BMR of oriental (Eastern countries) female students living in USA is on an average 10% below the standard BMR for American women of the same age-groups. • High values 33% above normal have been reported in Eskimos.

  19. State of Nutrition BMR is low in conditions of mal nutrition, starvation and wasting diseases.

  20. Barometric Pressure • Moderate reduction of atmospheric pressure does not affect the BMR, but a fall of pressure to ½ an atmosphere (viz. O2 tension 75 mm Hg), as occurs in mountain climbing increases BMR, but increased pressure of O2 does not raise BMR.

  21. Profession • Athletes, Soldiers and Manual workers have a slight higher BMR than persons leading a sedentary life

  22. Drugs • Quite a number of drugs like • Caffeine, • Benzedrine • Epinephrine, • Nicotine, • Alcohol, etc. increase the BMR • Reverse is observed with most of the anesthetics

  23. Hormones • Circulating levels of hormones secreted by thyroid, adrenal medulla and anterior pituitary increase BMR • The Stimulant effect on rate of metabolism and Heat production. • BMR raised in Hyperthyroidism • BMR Low in Hypothyroidism • One mg of thyroxin increases BMR by about 1000 C..

  24. Thyrotoxicosis • BMR may increase by 50 to 100% above normal, but RQ remains unaltered since both 02 consumption and CO2 production increase proportionately in such cases

  25. Myxoedema • BMR is diminished to 30% or even 45% below normal. • Anterior pituitary through its TSH affects BMR. • Growth Hormone also causes about 20% rise in BMR, • catecholamine increase BMR by about 20% of the resting value. • Male sex hormones cause a 10% increase in BMR.

  26. IMPORTANT TO NOTE • As all other factors are taken care of in the definition of BMR, therefore thyroid functiondetermines the changes in BMR

  27. Pregnancy • The BMR of pregnant mother after six months of gestation rises. • It may be noted in pregnancy that the BMR of the mother is the sum total of her own metabolism as in her non-pregnant state and Combined with that of the fetus hence pregnancy exerts no specific effect upon BMR.

  28. CLINICAL ASPECT: Pathological Variations in BMR 1. Fever: • Infections and febrile diseases elevate the BMR, usually in proportion to the increase in temperature

  29. Diseases • Characterized by increased activity of cells which also increase heat production due to increased cellular activity. Thus, BMR may increase in such diseases as: • Leukaemias(21 to 80%) • Polycythemia / Some types of anaemias, (10 to 40%) • Cardiac failure/Hyper­tension and • Dyspnoea(25-80%) .

  30. Endocrine diseases • The most important factor which alters BMR is the state of function of thyroid. • In fact, determination of BMR is mainly used for the assessment of thyroid function.

  31. Endocrine diseases • In hyperthyroidism, BMR is increased to + 75% or more. • In hypothyroidism (myxoedema), BMR is reduced to 40% or more. • BMR is also increased in Cushing's disease and Cushing's syndrome and also in Acromegaly. • BMR is decreased in Addison's disease (Hypo­function of Adrenal cortex

  32. Importance of BMR • As a diagnostic aid:For the diagnosis of various pathological conditions specially assessing the thyroid function (specially useful where hormone assays and isotope laboratory is not available).

  33. For calculation of caloric requirements • Essential in the calculation of calorie requirements of an individual for prescribing a diet of adequate calorific value and planning nutrition for individuals as well as communities and populations at large.

  34. Specific dynamic action and physical activity levels are the important attributes of Basal Energy Expenditure.

  35. Specific Dynamic Action • Also known as thermogenic effect of food. • Increased heat production following the intake of food. • Energy expenditure on digestion and absorption. • Trapped from energy stores • Actual energy from food is less than theoretical content • Activation energy needed for a chemical reaction and is to be supplied initially

  36. EXAMPLE A person takes 250 grams of carbohydrates • Should produce 250 x4 =1000 Kcal • 10% needed for activation = 100 kcal • Actual energy available = 900 Kcal • If requirement is really =1000 Kcal Then the person should actually take an amount capable of providing 1100 Kcali.e.275 grams

  37. SDA Values • Carbohydrates 05% • Protiens 30% • Fats 15% • Mixed Diet 10%

  38. Physical Activity Level (PAL)

  39. Energy Requirement and Occupation

  40. Calculation for energy requirement for a 55 kg person doing moderate work • For BMR = 24 x 55 kg = 1320 kcal • + For activity = 40% of BMR = 528 kcal • Subtotal = 1320 + 528 = 1848 kcal • + Need for SDA = 1848 x 10% = 185 kcal • Total = 1848 + 185 = 2033 kcal • Round to nearest multiple of 50 = 2050 kcal

  41. Proximate Principles • Carbohydrates • Fat • Proteins • Minerals • Vitamins Additional requirements for growth pregnancy lactation and convalescence are to be provided in the food.

  42. Volume of CO2 produced = RQ Volume of O2 consumed Respiratory Quotient • When food is oxidized, whether in an open system or closed biological system, oxygen is consumed and CO2 produced. Ratio in steady state / Unit time

  43. 6CO2 6O2 = 1 RQ = • Carbohydrates are completely oxidized and the volume of O2 used is equal to CO2 produced C6H12O6 + 6O2 6CO2 + 6H2O

  44. Fats C57H104O6 + 80 O2 57 CO2 + 52 H2O RQ = 57 = 0.71 80 Other fats have RQ  0.70

  45. Proteins RQ of proteins is a little complex to determine as it contain N & S in addition to C, H, O. Using specialized technique the RQ is found to be 0.82

  46. C2O5OH + 3O2 2CO2 + 3H2O RQ = 2/3 = 0.67 Alcohol

  47. Human • Use normally mix type of food • RQ of an intact person naturally will be the sum of RQ of all the three major type of food. • Carbohydrates • Fats • Proteins

  48. Postabsorptive State No food being consumed in preceding 12 – 14 hours RQ = 0.82 Ordinary mixed diet RQ = 0.85

  49. When diet is rich in Carbohydrates the RQ will be more close to one i.e. High More fats = Lower RQ

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