Most biologically active factors in foodstuffs exert multifunctional activities, and are able to contribute to the prevention of various diseases. In addition, some food components exert synergic effect. Combined use of such components makes it possible to decrease the dose of individual factors to obtain predictable effects. Appropriate use of such multifunctional factors enables the production of multifunctional foods with higher activity and safety, but with lower production costs. To create such multifunctional foods, extensive and cooperative studies aimed at clarifying the mechanisms responsible for interactions between food components, their absorption and transportation, and changes occurring with aging, are necessary. Since even our preliminary studies are too extensive to describe here, a brief outline of the important findings related to the action of functional lipids, antioxidants and dietary fibers is presented.

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We investigated the effects of 4.75% (w/w) branched-chain amino acid (BCAA) supplementation in rats fed a vitamin B₆ (B6) -deficient diet. Five-week-old male Wistar rats were assigned to groups fed four different diets for 3 weeks as follows : 1) a 20% casein diet including sufficient B6 and non-supplemented BCAA (C group), 2) a B6-sufficient diet supplemented with BCAA (aaC group), 3) a B6-deficient diet of non-supplemented BCAA (D group), and 4) a B6-deficient diet supplemented with BCAA (aaD group). Half of the rats in the aaD group showed abnormal accumulation of triacylglycerols (TAG) in the liver. In the aaC group, serine dehydratase (SDH) activity was significantly higher than in the other three groups, and plasma levels of threonine, glycine and lysine were significantly lower than in the C group. We analyzed the statistical correlation between the parameters investigated in this study and the liver TAG content in the aaD group: this revealed negative correlations between the plasma levels of pyridoxal phosphate (PLP) and citrulline and liver SDH activity, and positive correlations with the plasma levels of threonine, glycine, tyrosine and lysine. These results suggest that a B6-sufficient diet supplemented with BCAA changes the amino acid metabolism of rats, and that a B6-deficient diet supplemented with BCAA causes multiple changes in amino acid metabolism accompanied by TAG accumulation in the liver of some rats.

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