Both food composition and architecture influence gut microbial outcomes through two kinetic mechanisms. First the relative dynamics of nutrient digestion/release and gastrointestinal passage determines the nature of the residual digesta that exits the small intestine and becomes available for nourishment of the large intestinal microbiota. For this reason, nutrient release rates should be included alongside composition in nutrition labelling (1) as well as providing a nutrition-relevant distinction between foods with different levels of processing (1, 2). Once in the large intestine, in vitro studies suggest that fermentation dynamics of residual digesta again depend on both composition and architecture, more so than microbial population types (3). Nutritionally beneficial carbohydrate fermentation depends on the linkage types present in oligo- and polysaccharides, with common (in the diet) linkages more likely to be broken and fermented rapidly. Networked forms of polysaccharides such as gels and plant cell walls are fermented slower than dissolved forms (3,4). In addition, whole plant foods deliver to the large intestine both polyphenols and other micronutrients adsorbed to cellulose as well as macronutrients encapsulated within intact plant cells. This diversity of nutrients available to the microbiota may be part of the mechanism underpinning the health benefits of diets rich in plant-based foods.