BALANCED DIETS                                           205

literature—have been so unsatisfactory, in fact, so largely fallacious, in the light of
findings of this institute during the past six years, especially as set forth in a very
recent paper by Kriss, Forbes and Miller,⁴ which places the problem of determining
specific dynamic effects of nutrients in a new and vastly improved position.

The new point of view and procedure depend upon Rubner's idea, ^{5' 6} of a
specific dynamic effect of body substance katabolized, from which follows the
hypothesis (Forbes, Braman and Kriss, ⁶) of a status of minimum heat production
of life in which the energy requirement of the animal would be rendered available
without waste of heat—that is, without energy expense of utilization ; heat incre-
ments (dynamic effects) as usually determined at planes of nutrition below energy
equilibrium being less than the true energy expense of utilization by the amount
of the dynamic effect of body nutrients katabolized (Forbes, Braman and Kriss⁷);
heat increments determined above maintenance, with the heat production of main-
tenance as the base value, therefore, representing the true energy expense of
nutrient utilization.

We are free to admit, however, that if—as we have concluded—net energy
values of individual foodstuffs are not constants, because of the supplementing
effects of food combination, in rations and other conditions affecting the economy
of food utilization then it is conceivable that, for similar reasons specific dynamic
effects of individual nutrients likewise are not constants. We have unpublished
results on conditions affecting specific dynamic action, and a second year's experi-
ments on the subject are in progress.

The recent studies of this institute on specific dynamic effects and their deter-
mination afford an improved basis of understanding and procedure from which to
investigate this question. In this connection I would propose that it would save
confusion to limit the term " specific dynamic effect " to signify the dynamic effect
of specific kinds of nutriment, and to use the equivalent term " heat increment "
to signify other dynamic effects—that is, those which are not specific of particular
kinds of nutriment.

             ⁴ Jour. Nutrition, 8 : 509—534.
            ⁵" Die Gesetze des Energieverbrauchs bei der Ernahrung ", Leipzig und Wien,
            1902, S. 370.
             ⁶ Jour. Agr. Research, 37 : 285, 1928.
             ⁷ —40 : 77, 1930.