A composition and a method for improving the gastrointestinal (GI) health of a human subject by promoting the activity of amylolytic and short-chain fatty acid (SCFA) producing (e.g. acetogenic and/or butyrogenic) microbes in the GI system of a human subject. The composition includes a mixture of microbiota accessible carbohydrates (MACs) that includes at least two different resistant starches and at least two different non-starch polysaccharides. A blend for inclusion in a dietary supplement includes, or is, the mixture.
