Abstract
Short-chain fatty acids (SCFAs), the end products of fermentation of dietary fibers by the anaerobic intestinal microbiota, have been shown to exert multiple beneficial effects on mammalian energy metabolism. The mechanisms underlying these effects are the subject of intensive research and encompass the complex interplay between diet, gut microbiota, and host energy metabolism. This review summarizes the role of SCFAs in host energy metabolism, starting from the production by the gut microbiota to the uptake by the host and ending with the effects on host metabolism. There are interesting leads on the underlying molecular mechanisms, but there are also many apparently contradictory results. A coherent understanding of the multilevel network in which SCFAs exert their effects is hampered by the lack of quantitative data on actual fluxes of SCFAs and metabolic processes regulated by SCFAs. In this review we address questions that, when answered, will bring us a great step forward in elucidating the role of SCFAs in mammalian energy metabolism.
Highlights
Short-chain fatty acids (SCFAs), the end products of fermentation of dietary fibers by the anaerobic intestinal microbiota, have been shown to exert multiple beneficial effects on mammalian energy metabolism
Cecal short-chain fatty acid (SCFA) concentrations increased when 10% of dietary wheat starch was replaced by inulin, but decreased again when fiber content was increased to 20% inulin (Table 1)
To the role as substrates, SCFA concentrations are sensed by specific G protein-coupled receptors (GPRs), which are involved in the regulation of lipid and glucose metabolism
Summary
Gut bacteria in the cecum and large intestine produce SCFAs mainly from nondigestible carbohydrates that pass the small intestine unaffected. The different types and amounts of nondigestible carbohydrates that reach the cecum and large intestine depend on the daily intake and type of food. Fermentation of the carbohydrates reaching the cecum yield 400–600 mmol SCFAs/day, which amounts to a production of SCFAs of 0.24–0.38 kg body weightϪ1 hϪ1, equivalent to ف10% of the human caloric requirements [31]. The in vivo SCFA production rates as well as the intestinal SCFA concentrations on different fibers are most relevant. As we discuss information on the cecal SCFA content is available in model organisms, but there is limited information about in vivo production rates. In humans measurement of the cecal SCFA concentration is almost impossible and in most cases conclusions about cecal and colonic metabolism are deduced from fecal content and in vitro studies
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