The effects of red pepper on thermogenesis and appetite in regular spicy food users and non-users
While some previous literature indicates that red pepper (RP) consumption confers weight management benefits, findings have been contradictory. It was posited that these inconsistencies related to poor control over characteristics of the subject population, such as failure to stratify results by habitual use of spicy foods. Consequently, this dissertation focused on the chemosensory impacts of RP, with two overall aims. The first was to characterize the attributes distinguishing regular spicy food users (≥ 3 times/week) from non-users (< 1 time/month). The second was to determine if RP affects thermogenesis and appetite, and if it does, whether these effects differ in users and non-users. Twenty-five healthy, lean men and women (aged 23.0 ± 0.5 y, BMI 22.6 ± 0.3 kg/m2, 13 users and 12 non-users) were enrolled in a randomized crossover trial in which a standardized quantity (1 g); preferred quantity (users 1.8 ± 0.3 g/meal, non-users 0.3 ± 0.1 g/meal); or no RP were ingested. Postprandial energy expenditure, respiratory quotient, core body and skin temperature, and subjective appetitive sensations were measured. Additionally, users and non-users were characterized for selected sensory, physiological, personality, and cultural attributes. Results suggest that prior experience is a stronger determinant of spicy food preference than inherent physiological responsiveness to noxious stimuli or personality traits. Furthermore, thermogenesis is increased with hedonically-acceptable RP doses, and fat oxidation is greater when RP is consumed orally, compared to in capsule form. This implies that RP’s effects on energy balance are due to a combination of sensory and metabolic inputs, and that oral exposure optimizes its contribution to energy balance. Furthermore, RP suppressed orexigenic sensations and subsequent energy intake in non-users, but not users, suggesting that individuals may become desensitized to RP’s effects with long-term spicy food use. Given that many individuals abstain from spicy foods due to the sensory burn elicited by capsaicin, the major pungent principle in hot RPs, a promising alternative for non-users is consumption of “CH-19 Sweet” RPs containing capsiate, a newly-identified non-pungent capsaicin analog. Therefore, the current state of knowledge on the thermogenic and appetitive effects of capsaicin and capsiate from foods and dietary supplements was critically reviewed. Evidence is ample to suggest that capsaicin and capsiate both enhance energy expenditure and diminish orexigenic sensations, but the magnitude of these effects is small. Manipulation of the diet with these compounds should aid weight management, albeit modestly. Finally, a secondary analysis compared data generated by the visual analog scale (VAS) and the general labeled magnitude scale (gLMS) to assess noxious stimuli sensitivity in regular spicy food users and non-users. Both scales are commonly used to evaluate chemosensory perceptions. Previous studies have demonstrated that the gLMS is a superior assessment tool for situations where individual differences in perceptual experience impact scale use (e.g., sensitivity to the bitter taste compound 6-n-propylthiouracil (PROP)). This has led some scientists to argue for exclusive use of the gLMS, rather than the VAS, to evaluate all sensory experiences. Given that individuals rarely expose themselves to extreme stimuli (e.g., staring at the sun or childbirth), it was hypothesized that the VAS would provide greater sensitivity than the gLMS when sensory exposures mimicked those encountered in real-world environments. In accordance with previous studies, when exposed to PROP, tasters (among whom experimental concentrations exceed the bitterness present in everyday foods) used a larger proportion of the gLMS than non-tasters. However, following real-world exposures to noxious chemical, thermal, tactile, and auditory stimuli, the VAS demonstrated greater scale usage and improved sensitivity. Slopes of the VAS and the gLMS were moderate to highly correlated both within (all subjects) and between groups (users versus non-users and men versus women). Variance was similar with both scales and did not differ by stimuli exposure level. These findings imply that scale choice should be guided by context, indicating that the VAS may be more suitable and informative for real-world exposures, while the gLMS is more fitting for extreme exposures or with individuals who react in an extreme way to common stimulus concentration.
Mattes, Purdue University.
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