Whole grains are not equal: the role of fiber structure and phytochemicals in health

Abstract

Precision nutrition seeks to optimize human health by tailoring dietary interventions to individual genetic, metabolic, microbial, and lifestyle profiles. In this context, whole grains (WGs) serve as ideal candidates, as their diverse fiber structures and grain-specific phytochemicals interact dynamically with host physiology and the gut microbiome. This review examines six widely consumed WGs: wheat (Triticum aestivum L.), rye (Secale cereale L.), oats (Avena sativa L.), barley (Hordeum vulgare L.), brown rice (Oryza sativa L.), and corn (Zea mays L.), focusing on their distinct dietary fiber and bioactive compounds. WGs should not be viewed as uniform fiber sources. The quantity, structural complexity, solubility, viscosity, and fermentability of fibers vary among different WGs, contributing to the distinct health benefits of each grain. Moreover, while these grains offer general nutritional benefits, each grain contains unique secondary metabolites. Key examples include alkylresorcinols (ARs) in wheat and rye, avenanthramides (AVAs) in oats, hordatines in barley, γ-oryzanols (γ-OZs) and tricin in rice, and polyamine-conjugated hydroxycinnamates (PACH) in corn. These grain-specific phytochemicals exert diverse pharmacodynamic effects across metabolic, inflammatory, and oxidative pathways. For instance, hordatines shows effects on cardiovascular and glycemic regulation; ARs, γ-OZs, and tricin support lipid homeostasis and colorectal cancer mitigation; AVAs possess anti-inflammatory and microbiota-modulating properties; and PACH contribute to antioxidant capacity. Such functional specificity positions WGs as strategic components in individualized nutrition frameworks, holding promise for disease prevention and health optimization within the paradigm of precision nutrition.