6I2.0I5.2:6I2.397.I
THE COMPOSITION AND DISTRIBUTION OF THE
FATTY SUBSTANCES OF THE HUMAN SUBJECT.
BY E. P. CATHCART AND D. P. CUTHBERTSON.

(Institute of Physiology and Department of Biochemistry,
Royal Infirmary, University of Glasgow.)
EVEN a very cursory study of the literature concerning the metabolismof the various proximate principles makes it plain that the available
information as regards the utilization of protein and carbohydrate, although far from complete, is abundant and varied, in comparison with
our knowledge of the metabolism of fat.
The evidence that fat does serve as a source of energy is clear andunequivocal; and that in starvation, when the drain of energy is longcontinued, it is the depot fat that is involved is also beyond question.
But in experiments of short duration we cannot say that this is so.
Modern investigations of the energy exchange in muscle work would
suggest that fat functions as a source of energy even in the presence ofcarbohydrate. Thus Krogh and Lindhard [1920] state: "The proportion of carbohydrate to fat catabolized is a function of the relative
available quantities of the two substances, and substantially the same
during rest and during muscular work." They also state that "neither
fats alone nor carbohydrates alone are suitable for the supply of theenergy requirements of the body, but that the catabolic disintegrationof either of these substances requires the presence and the simultaneous
catabolization of the other." We think it may now be taken as certainthat in all tissue metabolism, as evidenced at any rate by the respiratory
quotient, there is a varying quota of protein, carbohydrate and fat involved in the tissue oxidation processes. For the evaluation thereforeof the energy exchanges in the body, which depends on the nature of
the material oxidized, it is essential that some knowledge of the natureof the various possible available fats be gained. From whence is derived
the quota of fat oxidized in tissue combustion? Is it in the form ofneutral fat derived from the various depots; is it in the form of fatty
acids such as are found in combination in average neutral fat; is it in
the form of highly desaturated fatty acids as postulated by Leathes

350

E. P. CATHCART AND D. P. CUTHBERTSON.

and his co-workers, or is it in some more complex "lipoid" form? The
work of Zuntz [1911], Benedict and Cathcart [1913], Krogh and
Lindhard [1920], and Furusawa [1925] would seem to point to thepossibility that fat may be used as a source of energy for the muscles,
yet the work of Leathes [1906] and Winfield [1915] suggests thatneutral fat present even in muscle, the most active metabolic tissue,cannot, at any rate directly, be regarded as the source from which themuscle derives its energy.
Practically all the analyses of human fat which are available in theliterature have been made on adipose tissue. Generally no attempt has
been made to ensure the absence of lipides, cholesterol and allied substances from the material analysed, nor have corrections been made forthe presence of such compounds in the final calculation. Hence most of
the scanty data available are not beyond criticism.
One of the earliest observers, Chevreul [1823] reported fat as being
composed of 77-85 p.c. carbon, and 11-42 p.c. hydrogen. These figures
are the recalculated values of Schulze and Reinecke [1867] whocorrected Chevreul's figures for the new atomic weight of carbon.
Schulze and Reinecke [1867] in a more extended investigation on
the composition of animal fat included in their observations two analysesof human fat. Fat from the kidney yielded carbon 76x44 p.c., hydrogen
11x94 p.c.; and fat from the panniculus adiposus 76x80 p.c. carbon and11x94 p.c. hydrogen. The period of heating employed by these authors
for the purification of the fat from the tissue involved several days'
evaporation on a steam bath. More recent work has shown such amethod of purification to be inadmissible. Benedict and Osterberg[1901] have made more exact analyses using methods of extraction
which give an unchanged fat, but which are not applicable to the separation of muscle and liver fat. The tissues analysed were the panniculus
adiposus abdominalis and perinephric adipose tissue. The sources ofthese materials were from poorly nourished or emaciated old persons,the youngest aged 51, the remaining ranging from 70 to 92 years. These
workers noticed that generally the solid triglycerides, stearin and palmitin,settled leaving the liquid olein on top, an observation which the present
authors have confirmed. B enedict and Osterberg state "that in lightof the striking agreement between the samples as a whole the average
76-08 p.c. for carbon and 11*78 p.c. for hydrogen cannot be far fromcorrect, and probably would be little, if any, affected by a multiplicationof samples." In addition, Benedict and Osterberg determined thecalorie value of 1 g. of each of their fats analysed. The average value

HUMAN FATTY SUBSTANCES.

351

obtained was 9*523 large calories per gram at constant volume, or 9-538
per gram using Stohmann's correction [1890] for reduction to constantpressure. These analyses were the first to be performed on human fat
with the bomb calorimeter. the very earliest calorific determinations ofhuman fat had been made by Stohmann [1884] using a Lewis
Thomson calorimeter. Fat from the panniculus adiposus gave an
average value of 9-379 large calories per gram, and that from perinephricfat 9-427 large calories per gram. Later Stohmann [1890], using theBerthelot bomb calorimeter, found that his earlier values were toolow. His corrected values for human fat were 9-514 and 9-562 respectively. Zuntz and Loewy [1924] have given the following figures forthe composition of human fat: 76-10 p.c. carbon, 11-80 p.c. hydrogen,12-10 p.c. oxygen; respiratory quotient 0-7133 with a calorie value of
9-54 for 1 g. The calorie value of 1 litre of oxygen is given as 4 795.
On recalculating this latter value by means of the recently determinedweight of a litre of oxygen at 00 C. and 760 mm. [Baxter and Starkweather, 1924], viz. 1-4289 g., the figure obtained is 4*792.
As regards the composition of human fat, it is difficult to give exact
values as various factors play important determinate r8les such as thenature of the diet, the age of the subject, the exact position from which
the sample for analysis has been taken.
Heintz [1852] concluded that the basis of human fat was a mixtureof triolein, tripalmitin and tristearin. Jaeckle [1897] gave the composition of fat as stearic acid 4x9 to 6x3 p.c., palmitic acid 16x9 to 21x1 p.c.,oleic acid 65x6 to 86x7 p.c., unsaponifiable matter 0.33 p.c., and lecithine
0-084 p.c. More recently Erben [1900] found in human fat 1-18 p.c.
free fatty acids, 0-56 p.c. lecithine, and 117 p.c. cholesterol. Heidus chkaand Handritschk [1928] found no other fatty acids than oleic, palmitic
and stearic in a series of analyses of liver, heart, mesenteric and adipose
fat. Such observations would suggest that these impurities are notpresent in sufficient amount to alter appreciably analyses such as thoseof Benedict and Osterberg [1901] and of Zuntz and Loewy [1924]
on adipose fat. This may be true as regards adipose tissue proper, butthese substances must be reckoned with in the purification of fat fromsuch sources as liver and muscle.
Many factors have recently been elucidated which play a role in thedetermination of the character of the fat of adipose tissue. The natureof the food consumed may bring about wide variations in its composition.
Ellis and Hankins [1925], and Anderson and Mendel [1928] haveshown that diets rich in protein or carbohydrate produce "harder"- fats

352

E. P. CATHCART AND D. P. CUTHBERTSON.

than a diet containing higher amounts of fat. More striking still is theeffect of the type of fat in the food, e.g. the effect of coco-nut oil on the
Polynesians and fish fat on the Eskimos [Rosenfeld, 1902; Kn6pfelmacher, 1898].
Currie [1922] has quoted some hitherto unpublished results of
Duncan on the variation of the iodine value of normal human fat withthe age of the subject, a finding which had earlier been noted in "beef "animals by Moulton and Trowbridge [1909]. Jaeckle [1902] foundthat the iodine value of the three-day-old child's fat was 47, of the twoto three-weeks-old child 58, and of the adult 62-73. Later Duncan[1922] noted that under 11 years the iodine value was 44, from 16 to 19
years 60 9, from 20 to 25 years 61.0, 621 from 26 to 38 years, and 63-98
from 52 to 65 years of age. Duncan in forty-three cancer patientsfound an average of 72 6, the ages varying from 39 to 68 years.
The present series of analyses was performed with a view to determining if the fat obtained from muscle and liver differed appreciably
from the fat of adipose tissue in its elementary composition and caloric
value. The question of the role of the co-existent lipides and their composition is delayed for a subsequent communication.
The material was obtained from fourteen subjects of ages ranging
from 18 to 57, six of whom died from accidental injuries (B., E., K.,
L., M. and N.). The necropsy was in most cases within a few hours ofdeath, the bodies being kept in a refrigerator till required for examination.
METHOD OF EXTRACTION OF FAT FROM TISSUES.
The tissue was finely minced and extracted three times with absolute alcohol in thecold. This was followed by three extractions with ether in the cold. The alcoholic extracts
were combined, filtered, and the filtrate evaporated to dryness. The ethereal extracts weresimilarly treated. These and all subsequent evaporations were carried out under reducedpressure at a temperature not exceeding 450 C. To avoid bumping during the distillationof the various solvents a gentle stream of nitrogen bubbles was drawn through the solution
being distilled. This latter precaution was to minimize any tendency for oxidation of theunsaturated fatty acids.
The residues from these two evaporations were combined and extracted with ether inthe cold. This ethereal extract was filtered and concentrated to a small volume. To thissolution a small quantity of NaCl and five times its volume of acetone were added andthe mixture allowed to stand over night. In the morning the precipitated lipides were
filtered off and the filtrate evaporated to dryness. The residue from this evaporation was
dissolved in a small quantity of ether and again five times its volume of acetone added toremove any remaining lipide. This process was repeated a third time. The filtrate fromthis last acetone precipitation was evaporated to dryness and extracted with petroleum
ether. The petroleum ether extract was ifitered and evaporated to dryness. The fat obtained
was dried and stored in a vacuum desiccator over CaCI2 and P205 and was kept in thedark.

HUMAN FATTY SUBSTANCES.

353

It was found possible to precipitate out all the cholesterol of the subcutaneous fatty
extracts with digitonin, the digitonin, after filtering off the cholesterol complex, being

precipitated by the addition of excess petroleum. This process had to be repeated. In themuscle and liver extracts, however, owing to the presence of cholesteryl esters, all thecholesterol could not be precipitated out. Recourse was then made in all subsequentpreparations to the quantitative determination of the total cholesterol by the modified
Liebermann reaction. In calculating the final composition of the fats after analysis,correction was made for the cholesterol using the following figures: for the iodine value 135(determined by Holde using Wij s' solution, which gives approximately twice thetheoretical value), and for the calorie value of 1 g. 10-289 [Bills, Cox and Steel, 1929].
The figures for the amounts of cholesterol present are not appended, as they only signify
the amount present at the particular stage of purification of the neutral fat.
The elementary analyses were performed in triplicate, so also the caloric values.
A Berthelot bomb calorimeter was used. It was checked against pure benzoic andsalicylic acids. No heat was used in the process of sampling, only thorough mixing.
Nitrogen and phosphorus were tested for, and where present in appreciable amount thevalues were recorded and due allowance made in the final calculations. The nitrogen wasdetermined by combustion with H2S04 and subsequent nesslerization. Hydrogen peroxide(perhydrol) could not be used owing to the presence in it of acetamide. The phosphorus
was determined, subsequent to the oxidation of the fat by HNO3 and H2S04, by precipitation as ammonium phosphomolybdate and weighing directly. The calculated values foroxygen are included, also the respective respiratory quotients on the assumption thatthese fats are oxidized in the body to C02 and H20.
Iodine values were determined using Wijs' solution. The entire estimation was performed in a stoppered 500 c.c. bottle. This avoided the unnecessary transference of reagents,
etc. Blank determinations were made with each fresh batch of fats, and from day to day
during these operations.
In determining the calorie equivalent of a litre of oxygen used in the burning of thesefats the volume of 1 g. oxygen at 00C. and 760 mm. was taken as 06998 litre [Baxter
and Starkweather, 1924].
Attempts were made to determine the melting points of several of these fats, and theirfatty acids. No definite data were gained owing to the fact that these fats consist of
triglycerides of various melting points, and therefore the final point of disappearance isoften considerably higher than the temperature at which the main bulk fuses. The same
criticism applies in the reverse sense to the determination of the solidifying point.

DIsCUSSION OF ANALYTICAL DATA.
The fats of the panniculus adiposus abdominalis were pale yellow
in colour, the depth of colour varying somewhat with the distance fromthe skin surface. Whitish flakes of the more saturated triglycerides floatedthroughout the fat, tending later to sediment. These fats showed muchless liability to change their character with keeping, than did the liver
and muscle fats which tended to harden after storage for several weeks
in a desiccator. A muscle fat which had hardened into a wax-likematerial gave an elementary analysis of 68-42 p.c. carbon, 1054 p.c.
hydrogen, and 21-04 p.c. oxygen, the respiratory quotient being 0742,
the fuel value 7-71 large calories, and the iodine value 602.

E. P. CATHCART AND D. P. CUTHBERTSON.

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356

E. P. CATHCART AND D. P. CUTHBERTSON.

The fats of liver and muscle were fairly similar in appearance. They
were of a golden brown colour, the liver fat being slightly the softer.
There was also a greater degree of solidification of the saturated fats.
Exposure to the air even for a short space of time, as, for example,
during the process of weighing, resulted in an increased fluidity of allthese fats, and heating in a hot air oven for half an hour at 950 C. caused
considerable darkening.
The theoretical respiratory quotient for tristearin is 0-699, for tripalmitin 0 703, for triolein 0-7125, the percentage of oxygen in themolecule of these fats being 10x78, 11x91 and 10x86 respectively. It isapparent that the highest calculated respiratory quotient is not a property of the fat with the highest percentage of oxygen in its molecule,but that the respiratory quotient of the saturated fats decreases withincreasing complexity, and further, that the respiratory quotients of theunsaturated fats are higher than the corresponding members of thesaturated series. It will be noticed that in the present series of fat
analyses the iodine value of the adipose tissue fats is generally a little
lower than that of muscle fat and very much lower than that of normalliver. It is interesting to note the relatively great difference between
the iodine values of the normal liver fats and the values of the liver fatsof very stout women. The normal liver fats gave values ranging from
121 to 134, whilst those showing a visible fatty change gave values
ranging from 69 to 85. The elementary analyses of the fats of the panniculus adiposus abdominalis of the present series agree very closely withthe average values, 76-08 p.c. carbon, 11-78 p.c. hydrogen, and 12-14 p.c.
oxygen, determined by Benedict and Osterberg [1901], and the almost
identical values reported by Zuntz and Loewy [1924]. The respiratory
quotients for average fats as calculated by these workers are 0-712 and0-7133 respectively. As previously mentioned the majority of Benedict's
and Osterberg's subjects were elderly and in many cases emaciatedsubjects.
The analyses of the subcutaneous fats of two of the three very fat
women indicated little divergence from that of normal adipose tissue fat.
The carbon was slightly lower, the oxygen somewhat higher, the calculated respiratory quotient identical. The calorie value was practicallythe same as the normal average in one case and somewhat lower in theother. Elementary analyses of the outer and inner tangential layers ofcase J. revealed no real difference.
The liver fats were found to be more variable in composition, thecarbon values being distinctly lower and the oxygen values distinctly

HUMAN FATTY SUBSTANCES.

357

higher than the subcutaneous fats. The respiratory quotient was also
very variable, the average 0*719 being definitely higher than that of
adipose tissue fat. The calorie value also varied considerably, the averagevalue 9-11 being much below that of depot fat. In some respects theliver fats of the stout women were more closely allied to the adipose
tissue fats, particularly in Case I. The calorie value 9-52 in this case wasalso high.
As was rather to be expected the series of muscle fats presented avariable group. Although every effort was made to get rid of every
visible trace, the variable factor would appear to be the fat present in
the areolar connective tissue surrounding the bundles Muscles vary
greatly in regard to the amount of this material present. While it cannot
be termed the true muscle fat it is impossible to free the muscle surface
entirely of its presence. Muscle fat as determined by its elementary
analysis is very like liver fat. Again the average respiratory quotient ishigh, 0717, and the calorie value low, 9'23.
Both liver and muscle fats are much more readily oxidized than are
the fats of adipose tissue, and although all precautions were taken tominimize the risk of oxidation, such a possibility cannot be completely
ruled out of account.
It is possible also that, as the liver almost certainly receives therelatively saturated fats to work over into the desaturated forms, deathmay find the laboratory of the liver at various metabolic stages.
It is of interest that the analyses of the liver of Case G., who diedin diabetic coma, did not reveal any obvious deviation from the values
found in the other cases.
A practical point emerges from the consideration of the foregoingdata in connection with the determination of the energy expenditure.
If it be assumed, and we believe correctly, that the fat utilized, at least
for immediate combustion, is not that of the depots in the subcutaneous
tissue but the more highly oxygenated fats and probably more labilefats found in the muscle and liver, and if our analyses of these fats canbe accepted as reasonably accurate, then the data, as given either in
the Zuntz table or as modified by Lusk, must be somewhat changed.
If then a composite value from the liver and muscle analyses be employed and the table recalculated the following result (Table III) is
obtained.
It will be observed that there is naturally little change as we approacha respiratory quotient of unity when it is generally assumed that no fat
is undergoing combustion, but that with the lower respiratory quotients,

358

E. P. CATHCART AND D. P. CUTHBERTSON.
TABLE III. Significance of the non-protein respiratory quotient.
Percentage total
Calories per
Percentage total
02 consumed byheat fromlitre O2
Carbo-

Carbo-

Fat
Fat
R.Q.
hydratehydrateLusk's data from Zuntz and Schumburg (condensed):
0-707
0.0
100*0
0.0
100-0
0-75
14-7
85-3
15-6
84-4
0-80
31-7
68-3
33-4
66-6
0-85
51-2
48-8
50-7
49-3
0*90
65-9
34-1
67-5
32-5
0-95
82-9
17-1
84-0
16-0
1-00
100-0
0-0
0-0
100-0
New data from present analyses:
0*718
100.0
100-0
0-0
0-0
0-75
11-4
88-7
12-0
88-0
0-80
20-1
70-9
30-4
69-6
0-85
46-8
48-4
53-2
51-6
0.90
35-5
65-5
66-0
34-0
0-95
82-3
17-7
83-2
16-8
1-00
100-0
0-0
100-0
0-0

Values of

Lusk

Zuntz

4-686
4-739
4-801
4-862
4-924
4-985
5-047

4-829
4-875
4-921
4-967
5-012
5-058
4-735
4-770
4-827
4-881
4-936
4-992
5-047

the quotients which are more commonly met with in the determinationof the metabolic rate, the divergence becomes quite definite.

SUMMARY.
1. Elementary analyses of fat from the panniculus adiposus abdominalis of normal subjects gave an average value of 76-16 p.c. carbon,
11-82 p.c. hydrogen, and 11-98 p.c. oxygen. The average respiratory
quotient was 0-711; the average calorie value 9-505 cal. per g. atconstant volume, and the equivalent of 1 litre of oxygen at constantvolume was 4-75 cal. The average iodine value was 68-4.
Similar analyses of fat from two very stout women gave 75-28! c.
carbon, 11-79 p.c. hydrogen, and 12-41 p.c. oxygen; 0-712 for the respiratory quotient; 9-45 for the calorie value and 4-79 for the calorie
equivalent of a litre of oxygen at constant volume. The average iodine
value was 71.
2. Elementary analyses of liver fat practically free of lipoid gave
73-79 p.c. carbon, 11-42 p.c. hydrogen, and 14-36 p.c. oxygen. The
average respiratory quotient was 0-719, the average calorie value 9-11
and the calorie equivalent of a litre of oxygen at constant volume 4-65.
The average iodine value was 127.
The average iodine value of the fat from two abnormally fat women'slivers which demonstrated visible fatty change was 73.
3. From voluntary muscle fat practically freed of lipoid gave on

HUMAN FATTY SUBSTANCES.

359

elementary analyses 73417 p.c. carbon, 11-47 p.c. hydrogen, and 14*59 p.c.
oxygen. The average respiratory quotient was 0-717, the calorie valueof 1 g. 9-23 cal. at constant volume and the equivalent of 1 litre ofoxygen at constant volume 4-82 cal. The average iodine value was 74.
4. A modification is suggested on the basis of the new analyses ofthe values given in the Zuntz-S chumburg table, and of necessity of
the Lusk modification of this table, of the calorie values of 1 litre ofoxygen at different respiratory quotients.
We have much pleasure in offering our thanks to Mr S. L. Tompsettfor his technical assistance.
Part of the expenses were defrayed by a grant from the Government Grant Committeeof the Royal Society, for which we return our thanks.

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Moulton, C. R. and Trowbridge, P. F. (1909). J. Ind. Eng. Chem. 1, 761.
Rosenfeld, G. (1902). Chem. Z. p. 110, cit. Heiduschka.
Schulze, E. and Reinecke, A. (1867). Liebigs Ann. 142, 191.
Stohmann, F. (1890). J. prakt. Chem. 42, 361.
Winfield, G. (1915). J. Physiol. 49, 171.
Zuntz, N. (1911). Oppenheimer's Handbuch d. Biochem. 4, 826.
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Physiologie des Menschen, 1924, Leipzig.

360

E. P. CATHCART AND D. P. CUTHBERTSON.
APPENDIX A.

Calculation of heat offormation of human fat.
The thermal value due to the formation of a compound from its elements Ca, H2b andoc is equal to the thermal effect on direct formation of the products of combustion, aCO2
and bH2O. Using the symbols of Thomsen [1908] the equation of the combustion may
be written:

CaH2bOc + (2a + b - c)O =aCO2 + bH2O.
To express the heat of combustion the abbreviated formula J(QaH2bOC) may be used. Thus
the equation form of the above law may be written(Ca, H2b, OC) +JCaHOc=a (C, 02) +b (H2, 0).
In the calculations of the heats of formation we have utilized for the heat of formationof C02 from amorphous carbon, the value 96,960 cal. per g. atom [Favre and Silbermann, 1852] and for the heat of formation of liquid water the value 68,360 cal. per g. mol.
[Thomsen, 1908]. The respective figures per gram of C and H are therefore 8-080 and
34-180 kilocalories. Values for the heats of formation so calculated are at constantpressure.
Favre, P. A. and Silbermann, J. T. (1852). Ann. Chirn. phy8. 34, 357.
Thomsen, J. (1908). Thermochemi8try, trans. Burke. Longmans, London.
APPENDIX B.
The correction of the value of the heat of combustion of fat as determined at constantvolume to that at constant pressure, can be conveniently calculated by determining what
energy the apparatus would gain by gas entering the bomb to make up the deficientvolume.
If we assume a fat of constant composition C = 76 p.c., H =12 p.c., and 0=12 p.c.,then each gram of fat requires 2-864 g. oxygen. Each unit volume of oxygen is replacedby 0-708 of a unit volume of C02, leaving a volume equal to that filled by 0-292 x 2-864
at the original pressure. This volume is filled by internal expansion of the contents ofthe calorimeter. The temperature changes are negligible.
Work done by gas entering at constant pressure:
20fr =20ir x vol. of 0-292 x 2-864 g. oxygen at 0° C. (r = 1 atmosphere.)Now 1 g. mol. of oxygen at pressure ir has volume 22-4 litres, and 72v for 1 g. mol. of
oxygen at 0 C. =2 cal. per degree =2 x 273 cal.
x 2-864207r x vol. of 0 298 x 2.864= 2 x 273 x 0298
32
= 14 47 cal
If temperature 16°,
work done = 289 x73 = 15.32 cal.