Energy balance and thermogenesis in rats consuming nonstarch polysaccharides of various fermentabilities

The equivalents of dietary protein, fat, and available carbohydrate as fuels for maintenance (kJ apparent metabolizable energy/kJ maintenance requirement) are known from classical experiments and are similar across species; that for nonstarch polysaccharide (NSP) is undetermined.

Our objectives were to determine the energy equivalent of NSP and the thermic responses to NSP.

In a randomized block design, 120 rats were treated in groups of 10 for 28 d with a basal diet (control) supplemented with starch and 10 different NSP treatments in amounts between 38 and 92 g/kg basal diet. Cellulose and starch were references. Thermic responses, deduced from body-composition changes and modeling of energy disposition, and energy and substrate excretion were determined.

NSP had fermentabilities between 0.01 and 0.93 g/g intake. Fermentability, partial digestible energy, and net metabolizable energy values of NSP were closely related. Generally, 51% of apparent metabolizable energy from NSP (fermentable gross energy) met maintenance requirements. Diet (energy)-induced thermogenesis (DIT) was evident from whole diets. Fermentable NSP supplied net metabolizable energy and caused DIT. After DIT and fermentation were accounted for, NSP-induced thermogenesis was generally -2+/-4% (x+/-SEM) of gross NSP energy, except for an outlying pectic preparation, which was 33% (P< 0.1).

The energy equivalent of NSP was 196 (100/51) kJ/kJ, compared with 128, 105, and 100 for protein, fat, and glucose, respectively, from the classical experiments. With the exception of pectic NSP, NSP does not induce thermogenesis in excess of that associated with DIT and fermentation.