The best option to increase energy expenditure is by increas-
ing physical activity; however, the current obesogenic
environment makes this option often difficult or impossible
for most people(24). Alternatively, ingestion of compounds
with thermogenic properties in combination with energy
restriction might eventually lead to higher body weight loss.
Capsinoids share a similar molecular structure with capsai-
cin. These compounds may therefore have a capsaicin-like
effect on metabolic rate in human subjects since animal
studies support such a thermogenic effect(11,12). In human sub-
jects, Inoue et al.(14) assessed the effect of 3 and 10 mg/d of
encapsulated capsinoids for 4 weeks on metabolic rate and
respiratory quotient. No changes in these variables were
observed. However, when only overweight individuals were
included in the analysis, a larger increase in VO with the high-
2
est capsinoids dose v. placebo was detected. A similar but NS
increase in metabolic rate and fat oxidation was observed
(P,0•10), but without changes in respiratory quotient. Unfor-
tunately, the lack of normalization of metabolic rate for the
metabolically active body mass did not allow firm con-
clusions. In a recent study in overweight men, encapsulated
capsinoids (6 mg/d for 12 weeks) did not modify metabolic
rate, although a higher but NS increase in fat oxidation was
detected after the 12-week treatment period when compared
with the placebo group. However, the authors failed to nor-
malise their data for the metabolically active tissue before
and after intervention(15).
Several factors may explain the present results, including
the low doses and short exposure to capsinoids, a lack of
power to find significant differences or simply the absence
of thermogenic effect of capsinoids. The present study was
designed with the power to detect a 5 % effect in RMR or
approximately 300 kJ/d. After 2 h of metabolic rate measure-
ment, the differences in RMR after capsinoids ingestion
compared with placebo were well below our detection limit
and more importantly of no physiological importance on
body weight. Therefore, we are confident that the lack of
significant difference is not due to a type II error.