Another possibility is that the measurement of energy
expenditure was not of sufficient duration (only 120 min
after dosing) to detect an effect. Such an observation has
been made with sibutramine, a medication that is approved
for obesity and which has a small effect on energy expendi-
ture. Seagle et al.(25) did not find an effect of sibutramine
(10 mg or 30 mg/d) in obese women when they measured
RMR for only 3 h. However, Hansen et al.(26) measured
energy expenditure for 5•5 h after dosing with 30 mg sibutra-
mine compared with placebo in fed and fasted men. There
was a sibutramine-induced increase in energy expenditure of
about 3-5%. Data from mice also support the idea that
longer exposure to high doses of capsinoids may be required
to increase metabolic rate, since the thermogenic effect may
be mediated by upregulation of uncoupling proteins(12).
Alternatively, capsinoids might influence food intake by suppressing hunger and increasing satiety in human sub-
jects(27-29). We did not specifically assess food intake in the present study, although the symptoms’ questionnaire given to the volunteers included a question about hunger feelings. We found no difference in hunger across treatments.
In conclusion, a combination of longer exposure time and
higher capsinoids dose may be required to increase metabolic
rate in a physiologically meaningful way. Therefore, there is
still a need to investigate the potential long-term effects of
capsinoids on metabolic rate in human subjects. In conclusion,
the present study does not support the hypothesis that capsi-
noids can be helpful in increasing energy expenditure and
fat oxidation in human subjects, at least over 2h after
exposure. Long-term use of capsinoids needs to be further
tested to establish them as a potential weight control agent