Prediction of in vivo short-chain fatty acid production in hindgut fermenting mammals: problems and pitfalls

Short-chain fatty acids (SCFA) are considered to have important physiological functions. However, to prove this, SCFA must be determined, which is rather difficult as a lot of factors interfere with their production. This review focuses on the factors that influence the prediction of short-chain fatty acid formation in the large intestine of monogastric mammals. To mimic the in vivo situation, when predicting the amount of short-chain fatty acids produced from a certain substrate based on in vitro models, one has to estimate the amount of this substrate entering the large intestine, the retention time in the different parts of the large intestine, and the substrate fermentability. Instead of in vitro models, direct and indirect techniques may be used to measure short-chain fatty acid production in vivo. Direct techniques include the measurement of input and output or measuring differences in SCFA between portal and venous blood whereas indirect techniques measure the end products of fermentation. In this case, other factors have to be taken into account, including technical limitations and ethical considerations. In this review it is concluded that the choice for a method will rely on the purpose of the study taking into account the (dis)advantages of every method.