Ely Ruben in the last part of the 19th century thus found out the calorific values of food stuffs in vitro.

the two parameters are interrelated Bomb Calorimeter This device, built by the great Ely Rubber of Germany, can determine the amount of energy that can be liberated when a food stuff is completely oxidized An accurately weighted quantity of food is introduced into the 'bomb' (a strong cylindrical container made up of steel),completely oxidized by igniting the food electrically m an atmosphere of oxygen and the heat produced (because of the oxidation) is measured by kilometric principles The value obtained is the amount of energy hidden. (i. e . potential energy) within The food. Ely Ruben in the last part of the 19th century thus found out the calorific values of food stuffs in vitro. Subsequently, the amount of energy liberated by the food stuffs when they are oxidized within the body (in vivo) were also measured, notably by Benedict and Atwater. Their values are give below The values are approximate only Note, that the values obtained so far as fat and carbohydrate are concerned, by the bomb calorimeter, are same as those obtained when they are catabolized within the body. However, with The protein, The values differ, the bomb calorimeter gives higher values its explanation is as follows Carbohydrate and fat are completely oxidized within The body (by The biological processes) and therefore, for them, the values do not differ. But in case of protein, in our body, a part of protein, viz, nitrogen, in the form of urea, is excreted out (via urine) without oxidation (that is. protein oxidation in our body is incomplete), where as in the 'bomb' it is complete UNITS As already stated (chap. 7.2) the old unit for heat was calorie (= The amount of heat necessary To raise 1 gm. of pure waters temperature from 14.5*C To 15.5 *C). In physiology, as calorie is too small an unit, Kcal or Cal is usually used (1 Kcal= 1000 cal). Modern unit is joule Q) or K.J (Kilo Joule). Thus, 1 cal - 4.184 J. hence 1 Kcal = 4.184 KJ (Note :Kilo calorie can be written either as Kcal or as Cal.the C being capital) Methods of determination of metabolic rate (energy expenditure) Different methods are, known These methods can be classified as follows . Methods of determination of metabolic rate irect method Aim of this method is to determine the heat given out by an individual in 24 hours only the principle will be discussed: The subject stays within a specially canstructed chamber, called Benedict-At water chamber for a period of hours together. A pipe encircles the room and water Circulates through the pipe. The heat evolved by the subject escapes into The water of The pipe, so That by noting the (i) initial (= where water enters the room) and final (= where water leaves the room) temperatures of the water, and (ii) the volume of the water circulated during the period of observation, the total heat evolved by the subject during the period of observalion can be found out. Next, the period of observation and total body surface of the subject, in square meter, are found out. From this, heat evolved/hr/sq. m of body surface in Kcal can be expressed and is called the metabolic rate Melabolic rate is the amount of energy liberaled by a subject per hour per sq m of body surface area. The room is made up of such matenal that does not cause loss-or gain of heat to or from the exterior. The heat given out via the subject's excreta is also added. This method is absolutely accurate but very expensive and cumbersome and unsuitable Tor routine use Indirect Calonmetry In indirect calorimetry.the heat evolved is not directly measured Instead, two other parameters, viz, (i) the res-piratory quotient (RQ). and (ii) the oxygen utilized in a specific period, are measured. If these two data are known, energy expenditure can be calculated The principles involved in the indirect calorimentry (indirect method of determination of the metabolic rate) can be stated as follows At a given time, the body is utilizing a particular mixture of protein, carbohydrate and fat as a fuel. Oxidation of a fixed quantity of this mixture will produce an exact quantity of heat and will require an exact amount of oxygen Staled otherwise, when a particular fuel mixture is being used (oxidized) by the body, utilization of exactly one liter of oxygen will produce an exact quantity of heat [because one liter of O2 can oxidize only a fixed quantity, not more, not less, of This fuel mixture and a fixed quantity of fuel mixture when oxidized can produce a fined amount of heat]. What particular fuel mixture is burnt can be understood from the RQ In practice, as stated below, one simply has to know the heat equivalent of 1 liter of 02 at the given RQ. 2. The proportions of protein, carbohydrate and fat in The above mentioned fuel mixture varies from time to time, but the proportion can be found out by determining the respiratory quotient or RQ Thus, if The fuel mixture is known (which can be found out by the RO) and volume of oxygen utilized in a given period be determined, The heat produced bythe body in that given period can be found out If now the surface area of The body is determined, the metabolic rate becomes known Calorific Value of Oxygen When the body is utilizing purely glucose, utilization of exactly one liter of oxygen produces oxidation of that much amount of fuel (glucose) which produces 5 04 Kcal (21.1 KJ) of energy This value. 5.04 Kcal or 21 1 KJ is called the calorific value of (one liter) oxygen, when glucose (carbohydrate) is the fuel Similarly calorific value of O2, when protein or fat arethe fuels are 4. 83 Kcal (20.2 Kj) and 4.7 Kcal (19.7 KJ) respectively. However human beings ordinarily utilize a mixture of carbohydrate, protein and