Branched-chain amino acids (BCAAs: leucine, isoleucine, and valine) not only function as essential amino acids for protein synthesis but also regulate protein and glucose metabolism. It is very important to control the concentrations of BCAAs in order to maintain normal metabolic conditions. The human body is equipped with a system for BCAA catabolism, and this influences the concentrations of BCAAs in the body. Branched-chainα-ketoacid dehydrogenase complex (BCKDC), located at the second step of the catabolic system, is a rate-limiting enzyme of BCAA catabolism. BCKDC is regulated by covalent modification, and branched-chain α-ketoacid dehydrogenase kinase (BDK) is responsible for inactivation of the complex by phosphorylation. This review introduces studies conducted mainly by the authorʼs group and summarizes the regulation of BCAA catabolism.

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The milk fat globule membrane (MFGM) is rich in buttermilk, which is a by-product of butter manufacture. MFGM consists mainly of membrane proteins and glycerophospholipids. As part of a research survey of the dietary functions of MFGM, we examined its suppressive effects on the increase of transepidermal water loss (TEWL) via the dorsal skin of Hos:HR-1(HR-1) mice when the mice were exposed to conditions intended to induce an atopic dermatitis-like state. To clarify the mechanism whereby MFGM improves skin barrier function, we analyzed total RNA expression in the dorsal skin. The results indicated that the expression of cornified cell envelope (CE) genes was markedly increased in HR-1 mice with symptoms of impaired barrier function, but decreased significantly in HR-1 mice fed dietary MFGM. In a dietary test involving human individuals with skin disorders, dietary MFGM suppressed the increase of TEWL in facial skin under the dry conditions of winter in Hokkaido. These results suggest that dietary MFGM improves the epidermal barrier function of the skin by correcting the overexpression of CE genes.

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Coffee is one of the most popular beverages worldwide and has been reported to have various physiological effects. In this study, we investigated the effects of coffee intake on gastric myoelectrical activity and autonomic nervous activity in humans. We performed a randomized crossover study involving 24 healthy males (12 non-habitual and 12 habitual coffee drinkers). Before and after ingestion of bread rolls (285 kcal) with 260 mL of coffee, decaffeinated coffee, or water, gastric myoelectrical activity was measured by electrogastrography for 20 min. Autonomic nervous activity was evaluated by heart rate variability (HRV) power spectral analysis, before and 35 min after ingestion. After coffee intake, a significant increase in electrogastrographic normogastric power was observed, in comparison with water intake. Moreover, coffee ingestion increased the total spectral power of HRV in habitual drinkers in comparison with non-habitual drinkers. Our results suggest that coffee intake enhances gastric motility and autonomic nervous activity.

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