If we compare the fuel value of the diet with the subsequent increase in the heat production, we obtain a mathematical relationship which may properly be designated as the "cost of digestion." This designation is in harmony with a convenient phraseology for similar relationships which is finding increased usage in all economic and many industrial processes and is beginning to be used by physiologists.1

For a true measure of the cost of digestion, it is necessary to have an accurate measure of the total heat production. We may not therefore content ourselves, as is too frequently done, with the simple measurement of the maximum or peak effect of the food ingested, but it is absolutely necessary to continue the measurements until the basal values are again reached and the total increment in the heat which is chargeable to the ingestion of the particular diet studied has been obtained for the entire period of measurement. Unfortunately, in a considerable number of our observations the experimental period was not continued a sufficient length of time to insure the return of the metabolism to the basal value and hence in the large majority of cases our measurement of the cost of digestion is a low rather than a maximum value. This should be taken into consideration in any estimate of our values for the cost of digestion.

The data regarding the cost of digestion in the studies made of the various nutrients and diets have been collected and tabulated.

1See MacDonald, Proc. Roy. Soc. (B), 1915-17, 89, p. 394.

Table 249. - Cost Of Digestion Of Various Food Materials, Calorimeter Experiments

Food material, subject, and date.

Total amount of food.

Hours after food to end of experiment.

Duration of experiment.

Period of increment observed in experiment.1

Fuel value.

Total increment observed.

Cost of digestion.

CARBOHYDRATES.

Sucrose.

grams.

hr.

min.

hours.

hours.

cats.

cals.

p. ct.

A. H. M...Apr. 1, 1907..

191

8

15

8

6?

756

68

9

F. M. M..Jan. 31, 1910..

2100

4

48

5

3

2408

19

5

F. M. M. .Feb. 2, 1910..

2100

4

0

4

3

2408

16

4

A. W. W.May 28, 1907..

80

4

15

4

2

317

6

2

Maltrose-dextrose mixture.

Dr. R Feb. 21, 1907..

458

8

15

8

8

1,382

74

5

E. H. B...May 14, 1907..

431

8

0

8

6

1,301

39

3

A. H. M...Mar. 28, 1907..

307

8

30

8

8

927

94

10

A. L. L...May 13, 1907..

299

8

15

8

4?

902

40

4

J. J. C___Mar. 4, 1910..

2145

3

43

4

3

2449

41

9

Bananas and sugar.

H. R. D... Mar. 31, 1906..

31,276

8

0

8

6

1,562

107

7

H. R. D...Apr. 21, 1906..

31,274

10

15

10

10

1,561

137

9

A. H. M...Apr. 2,1906..

31,207

8

0

8

8

1,448

94

6

A. L. L. ..Apr. 19, 1906..

3862

12

15

12

6

1,147

72

6

A. L. L.. .Mar. 30, 1906..

3864

8

0

8

4

1,109

88

8

J. J. C...Apr. 7,1909..

3725

3

32

4

4

962

69

7

F. M. M.Apr. 8,1909..

3620

2

30

3

3

655

19

3

Bananas.

Dr. H....Feb. 14, 1910..

403

2

38

3

3

409

27

7

F. M. M..Feb. 8,1910..

400

3

43

4

1

406

-2

0

Dr. H.....Feb. 17, 1910..

397

3

41

4

3

403

21

5

Popcorn.

A. H. M...Apr. 10, 1907..

199

8

45

8

8

847

66

8

H. B. W...Apr. 9,1907..

187

9

0

8

8

796

39

5

Rice (boiled).

A. L. L.. .May 27, 1907..

652

8

30

8

4?

432

7

2

FAT...

Cream...

J. J. C... Mar. 22, 1910..

445

3

49

4

....

1,362

-20

-1

D. J. M...June 7,1910..

376

3

49

4

1,245

-2

0

D. J. M...June 3,1910..

398

2

45

3

3

1,060

20

2

H. R. D...Mar. 28, 1906..

399

8

0

8

8

860

18

2

A. H. M...Apr. 5,1906..

345

8

0

8

4

766

73

10

A. L. L...Mar. 27, 1906..

341

8

0

8

6

735

57

8

D. J. M...Mar. 23, 1910..

221

1

39

2

...

666

1

0

Butter and potato chips.

A. H. M...Mar. 25, 1907..

4454

8

15

8

8

3,202

125

4

E. H. B...Mar. 19, 1907..

4316

7

15

6

6

1,924

57

3

L. E. E...Mar. 14, 1910..

4206

4

40

5

1,512

36

2

A. H. M...May 15, 1907..

4218

8

15

8

4

1,503

28

2

A. W. W..Apr. 25, 1907..

4189

9

0

8

4

1,276

15

1

J. R......Mar. 21, 1910..

4187

4

43

5

5

1,266

11

1

J. J. C...Mar. 12, 1910..

4129

4

38

5

3

791

14

2

PROTEIN.

Beefsteak.

A. H. M...Apr. 5,1907..

777

9

0

8

8

1,305

136

10

A. W. W..Apr. 6,1907..

755

9

0

8

8

1,268

92

7

A. W. W..May 25, 1907..

373

8

15

8

6

981

45

5

A. H. M...May 24, 1907..

384

8

15

8

6

644

70

11

J. R......Dec. 4,1908..

418

9

30

8

8

603

104

17

F. M. M..Dec. 10, 1908..

217

9

15

8

3

364

24

7

F. M. M..Dec. 23, 1908..

208

7

0

6

5

349

17

5

L. E. E...Jan. 17, 1910..

163

7

30

5

5

245

47

19

F. M. M. .Jan. 20, 1910..

132

7

0

5!

2

221

10

5

Food material, subject, and date.

Total amount of food.

Hours after food to end of experiment.

Duration of experiment.

Period of increment observed in experiment.1

Fuel values.

Total increment observed.

C08t Of digestion.

protein - cont.

Beefsteak and bread.

grams.

hrs.

min.

hours.

hours.

cals.

cals.

p. ct.

F. M. M..Jan. 11, 1910..

5296

7

15

5

5

480

44

9

F. M. M..Jan. 12, 1910..

5237

6

0

5

2?

415

32

8

F. M. M..Jan. 14, 1910..

5225

6

15

5

5

399

46

12

Beefsteak and potato chips.

J. J. C... May 11, 1911..

5311

10

0

6

4 1/2

676

43

6

A. G. E...Jan. 23, 1911..

6292

3

45

3

3

566

12

2

V. G. Jan. 21, 1911..

6235

4

0

3

3

463

21

5

C. H. H.Jan. 18, 1911..

•233

3

30

3

3

460

15

3

J. C. C....Jan. 17, 1911..

6213

3

30

3

3

425

28

7

Glidine.

J. R May 10, 1910..

770

4

15

4

4

7267

40

15

J. R......May 5,1910..

70

4

30

4

4

262

51

19

J. J. C....May 9,1910..

45

5

0

4

4

168

38

23

L. E. E...May 3,1910..

45

4

30

4

4

168

13

8

L. E. E. ..May 11, 1910..

45

3

30

3

3?

168

5

3

Gluten and skim milk.

H. R. D...May 17, 1906..

•652

12

0

12

12

809

143

18

H.C. K...May 7,1906..

•772

8

0

8

8

558

55

10

H. R. D...May 2,1906..

8321

8

0

8

8

496

51

10

H. R. D...May 9,1906..

8320

12

0

12

10

487

76

16

Plasmon and skim milk.

H. R. D...May 4,1906..

•376

8

0

8

8

758

77

10

H. C. K...May 15, 1906..

9586

12

15

12

10?

728

62

9

MIXED NUTRIENTS.

Milk.

H. R. D...Mar. 21, 1906..

608

8

0

8

6

444

11

2

A. H. M...Mar. 23, 1906..

607

8

0

8

6

385

51

13

A. L. L....Mar. 22, 1906..

607

8

0

8

6

382

59

15

Supper.

H. L. H.June 14, 1910..

1,131

6

15

5

4

1,731

77

4

Heavy breakfast.

A. H. M...Feb. 16, 1906..

1,779

9

45

8

8

4,378

186

4

A. H. M...Feb. 19, 1906..

1,633

9

30

8

8

3,936

229

6

H. R. D...Feb. 21, 1906..

1,779

9

45

8

8

3,697

148

4

H. R. D...Feb. 17, 1906..

1,828

9

30

8

8

3,311

181

5

A. L. L.. .Feb. 13, 1906..

1,365

9

30

8

8

2,720

162

6

A. L. L...Feb. 15, 1906..

1,196

9

30

8

8

2,142

96

4

Heavy supper.

H. R. D...Apr. 10-11, 1906

1.664

19

15

20 1/4

19 1/4

3,442

334

10

A. L. L. ..Apr. 6- 7,1906

1,273

14

30

16

14 1/2

2,364

281

12

1These periods represent in each case the portion of the experiment in which increment of heat occurred as confirmed by increase in either or both of the other factors of metabolism. In experiments where no estimate is given, either the period of increment was not clearly defined or the amount of increment was actually negative.

2Also juice of one lemon; additional energy (11.5 cals.) included in fuel value.

3Amounts include sugar as follows: H. R. D., 103 grams each day; A. H. M., 86 grams; A. L. L., 99 grams each day; J. J. C, 77 grams; F. M. M., 9 grams.

4Amounts include potato chips as follows: A. H. M., March 25, 1907, 211 grams; May 15, 1907, 105 grams; E. H. B., 233 grams; L. E. E., 114 grams; A. W. W., 104 grams; J. R., 92 grams; J. J. C., 91 grams.

5Amounts include bread as follows: January 11,50 grams; January 12,38 grams; January 14,24 grams.

6Amounts include 20 grams potato chips, except for J. J. C., May 11, 1911, 41 grams.

7Also juice of one-half lemon; additional energy (5.6 cals.) included in fuel value.

8Amounts include gluten as follows: H. R. D., May 17, 1906, 153 grams; May 2 and 9, 1906, 100 grams each day; H. C. K., 66 grams.

9Amounts include plasmon products as follows: H. R. D., 170 grams; H. C. K., 147 grams.

Inasmuch as a considerable number of the calorimeter experiments continued for 8 or more hours and hence represent a fairly long period of time when the metabolism was measured, and, indeed, usually a much longer period than that represented by the respiration experiments, the data for the two classes of experiments are given separately, those for the calorimeter experiments being included in table 249 and those for the respiration experiments in table 250. We have, furthermore, subdivided the experiments according to the preponderance of carbohydrate, protein, or fat in the several diets. The experiments in each group have been arranged according to the fuel value of the food intake. The data given in table 249 for the calorimeter experiments will be considered first.

Table 250. - Cost Of Digestion Of Various Food Materials, Respiration Experiments

Food material, subject, and date.

Amount of food.

Period of observation.1

Fuel value.

Total increment observed.1

Cost of digestion.

CARBOHYDRATES.

Dextrose.

grams.

hrs.

min.

cals.

cals.

p. ct.

K. H. A.......May 14, 1912......

2100

4

7

2385

12

3

P. F.J........May 15, 1912......

2100

3

55

2385

6

2

Dr. P. R......May 3,1912......

2100

4

29

2385

19

5

J. C. C........Dec. 31, 1912......

3100

3

21

3380

12

3

J. J. C........Mar. 7, 1911......

3100

3

57

3380

35

9

L. E. E.......May 29, 1911......

3100

3

53

3380

18

5

C. H. H.......May 1,1911......

3100

6

6

3380

24

6

H. L.H.......May 24, 1911......

3100

3

41

3380

17

4

B. M. K.......Dec. 30, 1912......

100

5

0

374

21

6

A. J. 0........Dec. 11, 1914......

100

1

27

374

14

4

J. J. C........Dec. 28, 1910......

275

2

50

2292

8

3

V. G.......Dec. 29, 1910...

275

2

49

2292

15

5

J.J. C........Dec. 22, 1910......

375

1

43

3286

13

5

V. G.......Dec. 23, 1910..

375

3

59

3286

19

7

Levulose.

K. H. A.......May 18, 1912......

2100

3

38

2384

20

5

P. F. J........May 22, 1912......

2100

3

58

2384

20

5

J. P. C........Apr. 3,1911......

3100

5

24

3379

36

9

L. E. E.......May 22, 1911......

3100

3

51

3379

21

6

C. H. H.......May 16, 1911......

3100

5

35

3379

34

9

H. L. H.......June 1,1911......

3100

5

13

3379

24

6

A. J. O........Dec. 8,1914......

100

1

29

373

12

3

J. J. C........Jan. 4,1911......

275

1

15

2291

10

3

J. J. C........Dec. 31, 1910......

75

6

47

280

38

14

Sucrose.

Prof. C........Nov. 20, 1909......

4100

1

4

4422

15

4

Prof. C.....Nov. 22, 1909..

4100

1

42

4422

16

4

H. H. A.......Jan. 2, 1912......

2100

3

44

2408

36

9

L. E. E........May 15, 1911......

3100

2

34

3402

24

6

A. F. G.......May 20, 1911......

3100

3

52

3402

30

7

C. H. H.......May 10, 1911......

3100

3

3

3402

28

7

H. L. H.......May 17, 1911......

3100

3

7

3402

23

6

A. J. O........Dec. 29, 1914......

100

1

30

396

26

7

J. J. C........Dec. 6, 1910......

275

5

39

2309

27

9

J. J. C........Dec. 8,1910......

275

2

3

2309

11

4

J. J. C........Dec. 20, 1910......

275

2

52

2309

16

5

V. G........Nov. 18, 1910...

275

1

34

2309

9

3

V. G......Nov. 30, 1910..

275

3

54

2309

21

7

J. J. C........Nov. 22, 1910......

375

1

11

3303

10

3

V. G..........Nov. 21, 1910...

373

2

36

3295

12

4

Lactose.

K. H. A.......May 23, 1912......

2100

3

12

2385

10

3

L. E. E.......June 5, 1911......

5100

4

5

6381

22

6

C. H. H.......May 23, 1911......

3100

4

30

3379

22

6

H. L. H.......June 7,1911......

3100

3

38

3379

18

5

A. J. O........Jan. 4, 1915

100

1

32

374

19

5

Food material, subject, and date.

Amount of food.

Period of observation.1

Fuel value.

Total increment observed.1

Cost of digestion.

PROTEIN.

Beefsteak.

grams.

hrs. mins.

cals.

cals.

p. ct.

J. J. C........Apr. 25, 1911......

6377

5 16

6790

81

10

H. L. H.......May 20, 1914......

317

1 58

532

13

3

H. L. H.......July 1,1911......

249

11 42

418

138

33

H. G. E.......Dec. 12, 1914......

200

2 51

336

25

7

J. F. M.......Apr. 23, 1914......

198

2 19

332

19

6

J. K. M.......Nov. 26, 1912......

196

3 3

329

28

9

J. J. C........Nov. 3, 1910......

150

4 8

314

51

16

D. M.........Oct. 28, 1911......

7182

5 11

7305

86

28

Dr. S.........June 30, 1911......

177

6 35

298

56

19

A. J. 0........Nov. 17, 1914......

173

2 44

290

17

6

V.G......................Nov. 4, 1910....

150

2 39

281

24

9

V.G......................Nov. 7, 1910...

150

4 19

245

38

16

J. J. C........Nov. 8, 1910......

150

3 12

234

13

6

MIXED NUTRIENTS.

Milk (whole).

H. F. T.......July 14, 1911......

500

4 5

358

11

3

Mixed diet.

J. J. C........Feb. 28, 1911......

750

4 52

796

45

6

A. F..........Apr. 20, 1915......

344

3 27

468

19

4

1From the time when subject finished eating to the end of the last observation, except in cases when the increment of heat ended earlier. For details and method of computation, see tables 126 to 168, 215, 234, 246, and 247; also pp. 151 and 152.

2Also juice of one lemon; additional energy (11.5 cals.) included in fuel value.

3Also juice of one-half lemon; additional energy (5.6 cals.) included in fuel value.

4Also 200 grams coffee; additional energy (26 cals.) included in fuel value.

5Also juice of two-thirds lemon; additional energy (7.6 cals.) included in fuel value.

Includes 15 grams potato chips.

7Also a little butter; not included in amount or fuel value.

To indicate when the effect of the ingestion of food ceased, the duration of the increment has been included in table 249. Frequently the basal metabolism was not reached before the experiment ended; under these conditions the value given is doubtless too low, for it is impossible to assume that the period of increment was coincident with the length of the experiment. In many instances, however, the duration of increment was considerably shorter than the total experimental period. This was true in the calorimeter experiments with sucrose, the only pure carbohydrate studied with the calorimeter.

It may be noted that a number of 24-hour experiments with mixed diet have been omitted from this table. While the basal value was determined during a complete fast, it seems necessary to recognize the fact that the subsequent ingestion of food is made under conditions materially different from those of the procedure followed in practically all our experiments, since after a 24-hour fast the stimulating action of the food must first counteract the depressing effect of fasting. Experiments made under these conditions are hardly comparable with those made after only 12 hours without food, and the experiments with a basal value of 24 hours or more of fasting have not been included in the table.