Unit III-Nutrition

Dr. Sadaf KalamLecturerDept. of BiochemistrySt.Ann’s College for Women, Mehdipatnam, Hyderabad

Basal Metabolic RateBMR

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It determines basal metabolism, bymeasurement of oxygenconsumption. The 6 litre capacityfloat is fitted with chaincompensated counter balance. Athermometer is fitted on the float.Movements of the float are recordedby means of gravity writing ink pen,adjustable by a lever at thebottom. The recording cylinder 12”x6” is of the lift-off type, and is drivenby an electrical unit, giving twospeeds viz. One rev. In 20 minutesand one rev. in 4 minutes. Speed ischanged through a lever.

Francis Gano, U.S. chemist, 1870-1957. Benedict-Roth apparatus - adevice to measure the amount ofoxygen utilized in quiet breathingfor the estimation of the basalmetabolic rate.

Soda lime

Spirometer bell

CLOSED CIRCUIT METHOD

Pen

Rotatory cylinder covered with paper

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Description: The movement of alightweight water-sealed gasometerbell is transferred to a paper charton a rotating drum to recordrespiratory volumetric excursionsfor lung function studies. Paperspeeds of 0.04, 0.2, 1.2 and 2.0cm/second can be selected. Oxygenconsumption can be measured byincorporating a carbon dioxideabsorption canister into thebreathing circuit. This device couldbe used for measuring Vitalcapacity (VC), tidal volume (VT),inspiratory and expiratory reservevolumes (IRV ERVan), as well asForced Expiratory Volume (FEV1).

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SPECIFIC DYNAMIC ACTION OF FOODS

SDA

In an adult individual, whose BMR is 1600 C, is fed with justenough food to provide 1600 C and is kept under basalconditions (except that he is not under post absorptive state), itis found that his energy output has increased beyond the basaloutput of 1600.The increase varies with the type of food that has supplied thecalories.

This stimulant action of foods on the metabolism is knownas the “specific dynamic action” (SDA)orcalorigenic action of food.

The specific dynamic action of food is the amount of energy it takes to break a food down to its basic unit so that it can be absorbed by the bloodstream. This is represented as a percentage of calories spent to break down the food.

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Non-protein nitrogen (or NPN) is a term used in animalnutrition to refer collectively to components such as urea, biuret,uric acid, creatine and ammonia, which are not proteins but canbe converted into proteins by microbes in the ruminant stomach.Due to their lower cost compared to plant and animal proteinstheir inclusion in a diet can result in economic gain, but at toohigh levels cause a depression in growth and possible ammoniatoxicity (microbes convert NPN to ammonia first before usingthat to make protein.)

Proteins are now defined as compounds of carbon,hydrogen, oxygen, nitrogen, sulphur, and sometimesphosphorus, which contain nitrogen in a form which the bodycan use.

Nitrogenous substances are those which contain nitrogen, an element which is essential to the life of every cell.

Definition: SDA may be defined as “extra heat” production,over and above the actual heat ought to be produced outside froma given amount of food, when this food is metabolised inside thebody.The mechanism of stimulation is not clear.• Proteins have the greatest SDA, amounting toabout 30 per cent above its caloric value.• Carbohydrates cause an increase of about 5 per centor 6 per cent, and• Fats cause about 4 per cent• Ordinarily, the SDA of all together amounts toabout 6 per cent of the BMR.Explanation: The explanation for SDA is not clear.It cannot be due to a production of heat as a resultof digestion as used to be thought earlier, becausefeeding of the products of digestion is as effectiveas undigested substances. In fact, intravenousadministration of amino acids or glucose give riseto a SDA of the same order as results from feeding.

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The early studies relating to energy metabolism led to the discovery that the protein of the food differs in one marked respect from either carbohydrate or fat, by its great stimulating effect upon metabolic processes as measured by the rate of oxidation.This is illustrated by the following type of experiment: If a dog is observed when it has been for some hours without food, and the rate of energy metabolism carefully measured, it will be found that this remains constant within narrow limits so long as the animal remains at rest. If now it is fed liberally with either fat or carbohydrate and the observations on its energy metabolism are continued, there is observed a slight increase in metabolism which is the direct result of the utilization of these foods. If on the other hand, a liberal portion of protein rich food, such as meat is fed to the animal instead of the non-nitrogenous nutrients, there is a surprising acceleration of the metabolic processes, attended with a marked increase in energy set free within the tissues. This was first shown by Bidder and Schmidt in 1852. Their experimental animal was a cat. During a certain interval of time the animal used 50.18 grams of oxygen and eliminated from its lungs 53.52 grams of carbon dioxide. The animal was then allowed to eat all the meat it would consume and the observations continued. During a similar interval the cat used 103.84 grams of oxygen and respired 113.52 grams of carbon dioxide.

Specific dynamic action (SDA), also known as Thermic effect of food(TEF) or dietary induced thermogenesis (DIT). It is the amount ofenergy expenditure above the basal metabolic rate due to the cost ofprocessing food for use and storage.

All foodstuffs, after being ingested, increase the rate of heat productionthough the subject is in a basal state. This increased heat production dueto ingestion above the basal metabolic rate (B.M.R) is known asSpecific Dynamic Action (S.D.A) or calorigenic action of foods.Heat production by brown adipose tissue is activated after consumingfood which becomes an additional component of dietary inducesthermogenesis.Thermic effect of food is important component of metabolism alongwith RMR and EMR.Commonly used estimate of thermic effect of food is about 10% ofone’s caloric intake roughly.For e.g. dietary fat is very easy to process and has little thermic effect,while protein is hard to process and has a large thermic effect.

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The highest Specific Dynamic Action (S.D.A.)is shown by protein and is about 30%,whereas others, e.g., carbohydrate 6%, fatabout 4%.By this it is meant that, if a quantity of protein,carbohydrate or fat, each having energy valueof 100 calories, be given separately to ananimal (whose basal metabolism is 100 cal)the actual heat production will be 130,106 and104 calories respectively.The extra heat comes from the combustionof the tissue substances causing loss of bodyweight.

Facts About Specific Dynamic Action (S.D.A):i. Specific Dynamic Action (S.D.A.) starts within an hour of taking food,becomes maximum in about the third hour and is maintained at this level forseveral hours.ii. Liver is the site of S.D.A. of proteins, because proteins fail to exert S.D.A.after removal of liver. But it is not the seat of S.D.A. of carbohydrates and fats.Because the removal of liver does not affect it.iii. In fasting and under-nutrition the S.D.A. of all foodstuffs increases.iv. During positive nitrogen balance, S.D.A. of protein does not seem to occur.v. In order to exhibit S.D.A the animal must have a temperature above 33°C.Below this temperature the S.D.A. of foodstuffs becomes less and lessapparent.vi. The S.D.A. of protein cannot be utilised in any other way. It is a waste heatand lost.vii.But the case is different with fats and carbohydrates. Their S.D.A. can beutilised in the performance of work. Hence, when exercise is done with a foodcontaining these substances, the extra heat due to S.D.A. is not seen, because itbecomes used up in the energy exchanges underlying muscular action. For thisreason high protein diet is not suitable for heavy muscular work. S.D.A. ofprotein is useful in maintaining heat balance in cold climates.

Cause of Specific Dynamic Action:1. S.D.A. of Proteins:The following observations are significant: S.D.A. is not due to the synthesis of body proteins from the amino acids of

food. Because proteins do not exert any S.D.A. upon growing infants orupon those subjects where nitrogen balance is positive.

S.D.A. is not due to any specific-stimulating action of some amino acids.Although it is seen that S.D.A. of protein depends upon the followingamino acids only-glycine, alanine, glutamic acid, tyrosine andphenylalanine, yet it is not due to the effects of these amino- acids.Because they exert no S.D.A. in infants.

S.D.A. of protein is exerted only when proteins are breaking down.Breakdown of amino acid include three processes—first deamination,secondly, the changes undergone by the non-nitrogenous part, and thirdly,the changes undergone by the nitrogenous part. It has been shown that thefirst two processes are not responsible for S.D.A.

S.D.A of proteins is shown during the change undergone by thenitrogenous part. S.D.A. is largely associated with the nature ofdeamination, i.e., oxidative deamination [trans-formation into urea). ATPalso helps in the urea formation. For the synthesis of ATP energy isrequired which leads to increased metabolism.

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2. S.D.A. of Carbohydrates:It is suggested that it represents the energy liberated in excessof that required for the conversion of glucose into glycogen.After a fast, when glycogen store is depleted, ingested glucose(which is mostly converted into glycogen) exhibits pronouncedS.D.A. Glucose with thiamine exerts more S.D.A., sincethiamine promotes and accelerates fat synthesis fromcarbohydrate.3. S.D.A. of Fats:According to Lusk (Plethora theory), it is due to more rapidoxidation of fats in the cells owing to their increasedconcentration in the tissue fluids (plethora) after absorptiondue to rate of digestive product reaching the tissue exceeds therate of utilisation.Food ingested-Digestion-Digestive products-Absorption-fatsincrease in blood-reach tissues- rapid oxidation of fats in thecells increases

Conclusions:Three applications may be made of thesefacts:i. The high S.D.A. of proteins should be made use ofin cold climates by giving a protein rich food.ii. While prescribing adequate diet, proper allowanceshould be made for the S.D.A. of proteins, otherwisetissue substances will burn and the subject will loseweight.iii. B.M.R. of a subject should be determined avoidingthe period during which S.D.A. develops.

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Recommended dietary allowance (RDA)Recommended Dietary Allowance (RDA) the amounts ofselected nutrients considered adequate to meet the knownnutrient needs of healthy people.The RDA are based on scientific knowledge and have beenpresented by a committee of the Food and Nutrition Board(FNB) of the National Academy of Sciences (NAS).RDA is generally accepted throughout the world as a validsource of information. At least 40 different nations have as wellas organisations have published standards similar to the RDA.

Adequate Intakes (AI). The RDA reflect the average daily amount of anutrient considered adequate to meet the needs of most healthypeople. If there is insufficient evidence to determine an RDA, an AI isset.

The energy requirement of an individual has been defined by arecent international working group as:That level of energy intake from food which will balance energyexpenditure when the individual has a body size and composition,and level of physical activity, consistent with long-term good health;and which will allow for the maintenance of economically necessaryand socially desirable physical activity.In children and pregnant or lactating women the energy requirementincludes the energy needs associated with the deposition of tissues orsecretion of milk at rates consistent with good health (WHO, 1985).

For groups, recommended energy allowances represent the average needs ofindividuals.If energy intake is consistently above or below a person's requirement, achange in body energy stores can be expected. If the imbalance betweenintake and expenditure continues over long periods, changes in body weightor body composition will occur and may adversely affect health (see DHHS,1988; NRC, 1989).Recommended energy allowances are stipulated as kilocalories (kcal) perday of physiologically available energy (i.e., the amount of potential foodenergy that can be absorbed and utilized).Most food composition tables list physiologically available energy valuesbased on digestibility trials of specific foods conducted by Atwater (Merrilland Watt, 1955). These specific energy values have been confirmed by others(Bernstein et al., 1955; Southgate and Durnin, 1970).The conventional general energy conversion factors of 4 kcal/ g of foodprotein or food carbohydrate and 9 kcal/g of food fat (also derived byAtwater) are adequate for computation of the energy content of typical diets,but not of specific foods nor of diets based heavily on fibrous plant foods.Alcohol (ethanol) has a caloric value of 7 kcal/g, or 5.6 kcal/ml.

ESTIMATING ENERGY REQUIREMENTSTotal energy expenditure includes the energy expended at rest, in physicalactivity, and as a result of thermogenesis. These components, in turn, areaffected by several variables, including age, sex, body size andcomposition, genetic factors, energy intake, physiologic state (e.g., growth,pregnancy, lactation), coexisting pathological conditions, and ambienttemperature.Resting Energy ExpenditureUnless levels of physical activity are very high, resting energy expenditure(REE) is the largest component of total energy expenditure.REE represents the energy expended by a person at rest under conditions ofthermal neutrality.Basal metabolic rate (BMR) is more precisely defined as the REE measuredsoon after awakening in the morning, at least 12 hours after the last meal.REE is not usually measured under basal conditions. REE may include theresidual thermic effect of a previous meal and may be lower than BMRduring quiet sleep. In practice, BMR and REE differ by less than 10%, andthe terms are used interchangeably.

REE is closely correlated with measures of lean body mass(muscle mass).In individuals of similar age, sex, height, and weight, differencesin lean body mass account for approximately 80% of the variancein measured REE.Differences in lean body mass also account for most of theobserved difference in REE between men and women, andbetween younger and older adults of similar heights and weights.

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Physical ActivityFor most people, the second largest component of total energy expenditure is theenergy expended in physical activity.In the past, estimates of energy requirements were based in part on the differentphysical activity levels associated with different occupations.With the introduction of labor-saving machinery, occupational energyexpenditures and differences between occupations tended to decline.Renewed emphasis on physical fitness has led some people, but not all, toincrease recreational activity, such as walking, jogging, and sports, resulting ingreater variability in the discretionary component of energy expenditure. Thus,the traditional estimation of energy needs according to occupation is no longeradequate.For schoolchildren and people in sedentary occupations, long-term well-beingmay depend on increasing physical activity during leisure time.Indeed, for many people, increasing energy expenditure through activity may bea more effective way of maintaining health, including desirable body weight,than reduction in energy intake.Increased activity promotes fitness and allows a more generous intake of food,which makes for easier attainment of RDA levels of nutrients.

PregnancyPregnancy imposes additional energy needs because of added maternal tissues and growthof the fetus and placenta. For a full-term pregnancy, during which the mother has gained12.5 kg and has given birth to a 3.3-kg baby, total energy cost has been estimated to be80,000 kcal (Hytten and Leitch, 1971). This estimate has been used in considering energyallowances for pregnancy (WHO, 1985). Alternative assumptions concerning thecomposition of tissue gained, observations of energy intake by pregnant women, andmeasurement of resting metabolism have led to estimates as low as 45,000 kcal (Durnin,1986) and 68,000 kcal (van Raaij, 1989) to as high as 110,000 kcal (Forsum et al., 1988) asthe cost of pregnancy in healthy, well-nourished women.Epidemiological evidence suggests that adequate maternal weight gain, including somematernal fat storage, is needed to ensure that the size of the newborn is optimal for survival.Thus, storage of energy is included as part of the energy requirement of pregnancy.Metabolic requirements and physical activity may change during pregnancy, but there areno well-documented studies providing the data from which to estimate changes in energyallowance for these two factors.WHO (1985) estimated the energy allowance for pregnant women by dividing the grossenergy cost (80,000 kcal) by the approximate duration of pregnancy (250 days following thefirst month), yielding an average value (after rounding) of 300 kcal/day for the entirepregnancy. The present subcommittee accepts this calculation with the caution that anydiminution in activity with advancing pregnancy must be taken into account. Unless thewoman begins pregnancy with depleted body reserves, additional energy intake is probablynot required during the first trimester. An additional 300 kcal/day is recommended duringthe second and third trimesters.

LactationEnergy requirements for lactation are proportional to the quantity of milk produced. Theaverage energy content of human milk from well-nourished mothers is about 70 kcal/100ml (WHO, 1985). The efficiency with which maternal energy is converted to milk energyis assumed to be approximately 80% (range, 76 to 94%) (Sadurkis et al., 1988; Thomsonet al., 1970; WHO, 1985). Thus, approximately 85 kcal are required for every 100 ml ofmilk produced. Average milk secretion during the first 6 months of lactation is 750ml/day; in the second 6 months, it is 600 ml/day. The coefficient of variation is 12.5%.Thus, the average woman would require an additional 640 kcal and 510 kcal/day in thefirst and second 6 months, respectively. The upper boundary of requirements (+ 2 SD)would be 800 and 640 kcal.Energy allowances during lactation may be partially met by extra fat stored duringpregnancy. Such energy reserves, about 2 to 3 kg in women who gain 11 to 12 kg duringpregnancy, normally are utilized during the first few months of breastfeeding. These fatstores can theoretically provide about 100 to 150 kcal/day during a 6-month lactationperiod. Accordingly, an additional average allowance of 500 kcal/day is recommendedthroughout lactation, which, assuming appropriate weight gain during pregnancy, maypermit readjustment of maternal body fat stores upon termination of breastfeeding. Therecommended allowance for women whose gestational weight gain is subnormal, orwhose weight during lactation falls below the standard for their height and age, is anadditional 650 kcal/day during the first 6 months.

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Conclusion

Nutrition and health are directly related. Effects of poor nutrition are

cumulative. There are six essential nutrients:

carbohydrates, fats, proteins, minerals, vitamins, and water. Nutritional assessment is the best way

to determine deficiencies that may result from lack of nutrients.