Determination of energy value – physiological fuel value

Energy is the ability to work - energy value of food is expressed in kilocalories - Determination of energy value of food - physiological value of food can be understand

1. Determination of Energy Value –
Physiological Fuel Value
R.Subha, M.Sc., M.Phil., D.C.T.,
Assistant Professor of Home Science,
V.V.VanniaperumalCollege for Women,
Virudhunagar.

2. JOULES AND CALORIES
•The conversion factors for joules and calories
are: 1 kJ = 0.239 kcal; and 1 kcal = 4.184 kJ..

3. Physiological Fuel
•Based onthe composition of carbohydrate,
fat and proteinthe heat of combustion of the
feed sample can be worked out using
appropriate factors. From the gross chemical
composition of the feed samples the amount
of energy yielding nutrients namely
carbohydrate, fat and protein are estimated.

4. FLOW OF ENERGY THROUGH THE BODY -A BRIEF OVERVIEW
•Ingestedenergy(IE)orgrossenergy(GE)Foodthatisingestedcontainsenergy-themaximum
amountbeingreflectedintheheatthatismeasuredaftercompletecombustiontocarbondioxide
(CO
2)andwaterinabombcalorimeter.
•Faecalenergy(FE)andgaseousenergy(GaE)Incompletedigestionoffoodinthesmallintestine,in
somecasesaccompaniedbyfermentationofunabsorbedcarbohydrateinthecolon,resultsinlosses
ofenergyasfaecalenergy(FE)andso-calledgaseousenergy(GaE)intheformofcombustiblegases
(e.g.hydrogenandmethane).Short-chain(volatile)fattyacidsarealsoformedintheprocess,some
ofwhichareabsorbedandavailableasenergy.
•Urinaryenergy(UE)Mostoftheenergythatisabsorbedisavailabletohumanmetabolism,but
someislostasurinaryenergy(UE),mainlyintheformofnitrogenouswastecompoundsderived
fromincompletecatabolismofprotein.
•Surfaceenergy[SE]Asmallamountofenergyisalsolostfromthebodysurface.
•Metabolizableenergy[ME]Theenergythatremainsafteraccountingfortheimportantlossesis
knownas“metabolizableenergy”.
•Dietary-inducedthermogenesis(DIT)Notallmetabolizableenergyisavailablefortheproductionof
ATP.Someenergyisutilizedduringthemetabolicprocessesassociatedwithdigestion,absorption
andintermediarymetabolismoffoodandcanbemeasuredasheatproduction;thisisreferredtoas
dietary-inducedthermogenesis(DIT),orthermiceffectoffood,andvarieswiththetypeoffood
ingested.Thiscanbeconsideredanobligatoryenergyexpenditureand,theoretically,itcanbe
relatedtotheenergyfactorsassignedtofoods.
•NetMetabolizableEnergy(NME)Whentheenergylosttomicrobialfermentationandobligatory
thermogenesisaresubtractedfromME,theresultisanexpressionoftheenergycontentoffood,
whichisreferredtoasnetmetabolizableenergy(NME).

5. •Some energy is also lost as the heat produced by
metabolic processes associated with other forms of
thermogenesis, such as the effects of cold, hormones,
certain drugs, bioactive compounds and stimulants.
•In none of these cases is the amount of heat produced
dependent on the type of food ingested alone;
consequently, these energy losses have generally not
been taken into consideration when assigning energy
factors to foods.
•Net energy (NE) The energy that remains after
subtracting these heat losses from NME is referred to
as net energy for maintenance (NE), which is the
energy that can be used by the human to support basal
metabolism, physical activity and the energy needed
for growth, pregnancy and lactation.

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

7. •Amount of energy available to the body from
a given amount of nutrient is called as
Physiological Fuel Value.
•Bomb caloriemeter –CHO, Fat and Protein -
oxidised completely.
•Human body –process of digestion not
proceed 100% -efficiency with which nutrient
is digested must be taken into account.
•Coefficient of digestibility –express the
proportion of ingested nutrient which
becomes available to the cells of the body.

8. Calculation -Physiological Fuel
Value/ Atwater Bryant Factors
CHO Fat Protein
Heat of combustion 4.15 9.45 5.65
Energy from
combustion of
Nitrogen
unavailable to the
body
- - 1.30
Net heat of
combustion
4.15 9.45 4.35
Coeffficientof
digestibility
0.98 0.95 0.92
Physiological Fuel
Value (Kcal)
4.00 9.00 4.00
Physiological Fuel
Value (KJ)
17.00 38.00 17.00

10. Reference
•Srilakshmi. B, 2018. Nutrition Science, 6
th
edition. New Age International Pvt Ltd, New
Delhi.
•https://www.biologydiscussion.com/energy/m
etabolism-energy/how-to-measure-calorific-
value-of-food/17321