A search for effective components of food flavor that stimulate energy expenditure and the analysis of its neuro-hormonal mechanism

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The object of this study was to (1)explore and identify effective components of food flavor that stimulates energy expenditure in the body, and (2)to elucidate the actions of centrally-acting neuropeptides that regulate food intake on energy expenditure by analyzing whole-body oxygen consumption (VO2) and the respiratory quotient(RQ).1.On the first category of the studies, we examined the effects of ginger and raspberry and their effective components, zingerone and raspberry ketone, on VO2 and RQ in rats fed a high-carbohydrate diet or a high-fat(lard) diet. Addition of 2% ginger powder or 0.4% zingerone to both diets caused significant increase in 12-h cumulative VO2 during the dark(feeding) period. The RQ value during the period was reduced significantly by the addition of ginger or zingerone. Similarly, addition of 0.4〜5% raspberry ketone to the both diets caused dose-dependent increases in the cumulative VO2 and decreases in the RQ values. In addition, addition of raspberry ketone to the high-fat diet prevented the accumulation of triglycerides in adipose tissues and liver, and amended disorder of lipid metabolism induced in rats fed the high-fat diet for 4 weeks.2.Among orexigenic substances, orexin-A administered into the third ventricle of rats caused a marked increase in VO2, but conversely noradrenaline(NA) decreased VO2. transiently Intracerebroventricular microinjection of neuropeptide Y and ghrelin increased the RQ values, but NA caused transient decrease in the RQ. However, central injection of galanin, orexin-B, or melanin-concentrating hormone did not affect both the VO2 and RQ values significantly.Among anorexigenic neuropeptides, on the other hand, leptin caused a decrease in RQ but did not affect significantly the cumulative VO2 during the dark period By contrast, microinjection of corticotropin-releasing hormone was found to reduce RQ and increase the cumulative VO2.