Phenolic acids in brown rice attenuate postprandial inflammation in sedentary office workers: mechanisms and implications

Introduction The sedentary lifestyle threatens modern office workers, exacerbated by shrinking exercise spaces and excessive screen time.[1] Workers spend 75% of their working hours sitting, reducing opportunities for physical activity.[2,3] Heinonen et al[4] linked sedentary behavior to obesity, with unhealthy eating habits as a potential mediator. Sedentary behavior, dietary patterns, and postprandial inflammation Prolonged sedentary behavior impairs glucose metabolism and promotes chronic low-grade inflammation.[3] Ebrahimi et al[5] link the lack of physical activity with fasting state chronic inflammation. Mechanistically, physical inactivity exacerbates acute hyperglycemia by reducing myokine interleukin (IL)-6 secretion and GLUT4 translocation. Although IL-6 is often pro-inflammatory, when released by skeletal muscle during exercise (as a myokine), it exerts anti-inflammatory effects (pleiotropic effects) and enhances metabolic regulation, including glucose and lipid metabolism. Furthermore, exercise also induced GLUT4 translocation that facilitates glucose uptake in skeletal muscle.[6–8] Consequently, lack of physical activity ultimately disrupts these pathways promoting pro-inflammatory state that increases the risk of cardiovascular diseases, insulin resistance, and type 2 diabetes mellitus.[9] Dietary choices further modulate these effects.[10] Acute dietary exposure—particularly a single meal—can transiently elevate inflammatory markers, a phenomenon termed “postprandial inflammation.”[5] While postprandial inflammation normally represents a localized defense with minimal systemic effects, persistent or exaggerated postprandial reactions could gradually increase overall inflammation.[10] This is concerning since the postprandial state can last for up to 16 h/day during which the body digests and absorbs nutrients.[11] Emerging evidence suggests sustained postprandial inflammation underpins chronic low-grade inflammation, a precursor to metabolic diseases.[5,10,11] Sedentary office workers frequently exhibit a dietary pattern high in fast food, sugary foods, and energy-dense meals, but low in fruits, dairy, nuts, and whole grains. External factors like prolonged screen time, social media use, and workplace environments that promote meal skipping further worsen these habits.[12–16] These suboptimal dietary preferences significantly influence postprandial responses. Following meal consumption, dietary carbohydrates undergo enzymatic breakdown into glucose, leading to acute hyperglycemia. Glucose metabolism generates reactive oxygen species (ROS) as byproducts, leading to oxidative stress and tissue inflammation. Furthermore, hyperglycemia activates alternative metabolic pathways (eg, pentose phosphate, polyol, and hexosamine pathways), amplifying oxidative stress and activating pro-inflammatory nuclear factor kappa B (NF-kB) transcription factor leading to increased cytokine production (tumor necrosis factor-α [TNF-α], IL-1β, IL-6).[17–19] Over time, the synergy of physical inactivity and poor diet escalates risks for chronic low-grade inflammation. Therefore, glycemic modulation and cellular glucose uptake regulation constitute critical determinants of metabolic health. Optimizing rice selection for postprandial health Given the importance of glycemic modulation in mitigating oxidative stress and inflammation, dietary interventions—particularly the strategic selection of carbohydrate sources—emerge as a practical approach to attenuate postprandial inflammation. As a global staple and major macronutrient source,[20] rice represents a key opportunity for such interventions. However, current consumption heavily favors refined white rice, despite brown rice offers superior nutritional value as a whole grain rich in bioactive compounds.[21] The bran and germ layers of brown rice contain the majority of its polyphenols, present in both soluble glycoside and free aglycone forms.[22] Clinical evidence demonstrates that whole grain consumption significantly reduces inflammatory markers (C-reactive protein [CRP], IL-6, TNF-α) in overweight individuals and patients with type 2 diabetes or metabolic syndrome.[23,24] Nutritionally, brown rice surpasses white rice through higher fiber, resulting in lower glycemic index (GI) and glycemic load (GL). This distinction carries clinical significance, as high-GI/GL carbohydrates may trigger inflammatory pathways via NF-κB activation.[25] The mechanistic relationship between high-fiber, lower GI diets, and reduced systemic inflammation highlights the importance of rice selection.[19,26] Although many studies aggregating whole grains in general, obscuring the unique effects of brown rice phenolic acids, research by Callcott et al[27] demonstrated its postprandial benefits. Brown rice enhances antioxidant activity and reduces oxidative stress (as measured by malondialdehyde [MDA]) and pro-inflammatory cytokines (TNF-α, IL-6, IL-8, IL-10, and IL-12) in both obese and healthy individuals.[27,28] However, human trials and mechanistic studies on its acute postprandial anti-inflammatory effects are limited. Phenolic acids in brown rice Brown rice is a whole grain, retaining its bran (6%–7%), germ (2%–3%), and endosperm (90%) after harvesting.[20] The bran and germ are rich in polyphenols and dietary fiber (Figure 1). Its polyphenols include flavonoids (including proanthocyanidins—responsible for its red color, anthocyanins, isoflavonoids, and flavones) and non-flavonoids (such as phenolic acids, stilbenes, and phenolic amides). Phenolic acids represent the most abundant non-flavonoid polyphenols in brown rice, originally serving roles in plant growth, disease resistance, and pigmentation.[22,29]Figure 1:: Brown rice structure and its polyphenol content.Phenolic acids in brown rice include hydroxybenzoates (gallic acid, vanillic acid, syringic acid) and hydroxycinnamates (ferulic acid and sinapic acid [SIA]) which possess antioxidant aromatic ring with hydroxyl (-OH) groups.[30] They exist in three forms: soluble-free, soluble-conjugated, and insoluble-bound (Figure 2). The soluble-free form is readily absorbed in the stomach and small intestine, enabling systemic distribution to prevent biological macromolecule oxidation by free radicals. In contrast, soluble-conjugated and insoluble-bound forms require enzymatic digestion or gut microbial action to become bioavailable.[31]Figure 2:: Phenolic acids in brown rice, forms and acute effects on inflammation and oxidative stress. CAT, catalase; COX2, cyclooxygenase 2; CXCL2, C-X-C motif chemokine ligand 2; GA, gallic acid; HO-1, heme oxygenase-1; IL-1β, interleukin-1β; IL-6, interleukin-6; IL-8, interleukin-8; IL-10, interleukin-10; MAPKs, mitogen-activated protein kinases; MCP-1, monocyte chemoattractant protein-1; MMPs, matrix metalloproteinases; NF-κB, nuclear factor kappa B; NLRP3, NOD-like receptor protein 3; NO, nitric oxide; NQO1, NAD(P)H quinone dehydrogenase 1; NRF2, nuclear factor erythroid 2-related factor 2; ROS, reactive oxygen species; SIA, sinapic acid; SOD, superoxide dismutase; SYA, syringic acid; tFA, trans-ferulic acid; TGF-β, transforming growth factor-β; TIMP-1, tissue inhibitors of metalloproteinase-1; TNF-α, tumor necrosis factor-α; VA, vanillic acid.In vivo studies demonstrate that brown rice consumption acutely enhances antioxidant status and reduces proinflammatory cytokines, suggesting rapid postprandial bioavailability of its polyphenols.[27] This effect is likely attributable to soluble-free form of gallic acid (GA), vanillic acid (VA), syringic acid (SYA), ferulic acid (FA), and SIA which reach peak plasma concentrations within 30 minutes. These compounds inhibit the NF-κB, mitogen-activated protein kinases (MAPK), and NOD-like receptor protein 3 (NLRP3) pathways, reduce ROS production, and activate the NRF2 pathway—upregulating antioxidant proteins (heme oxygenase-1 [HO-1], NAD(P)H quinone dehydrogenase 1 [NQO-1], catalase [CAT], superoxide dismutase [SOD]) while suppressing pro-inflammatory mediators (TNF-α, transforming growth factor-β [TGF-β], IL-1β, IL-6, IL-8, IL-10, monocyte chemoattractant protein-1 [MCP-1], matrix metalloproteinases [MMPs], tissue inhibitors of metalloproteinase-1 [TIMP-1], nitric oxide [NO], prostaglandin E2 [PGE2], C-X-C motif chemokine ligand 2 [CXCL2], and cyclooxygenase 2 [COX-2])[32–38] (Figure 3). In contrast, larger polyphenols like proanthocyanidins are poorly absorbed (8%–17%) and rely on microbial conversion.[22,27] Thus, these findings suggest that the acute postprandial anti-inflammatory and antioxidant effects of brown rice are stem primarily from the rapid bioavailability of free phenolic acids.Figure 3:: Molecular mechanism of phenolic acids in antioxidation and anti-inflammation. AP-1, activator protein 1; ARE, antioxidant response element; c-Fos, c-Fos proto-oncogene protein; c-Jun, c-Jun proto-oncogene protein; Caspase-1, cysteine-aspartic protease 1; ERK, extracellular regulated kinase; IKK, IkappaB kinase; IKKa, inhibitor-κB kinase alpha; IL-1β, interleukin-1β; JNK, c-Jun N-terminal kinase; KEAP1, cytoplasmic Kelch-like epichlorohydrin-associated protein 1; MAPKs, mitogen-activated protein kinases; NF-κB, nuclear factor kappa B; NLRP3, NOD-like receptor protein 3; NRF2, nuclear factor erythroid 2-related factor 2; PA, phenolic acids; PPARγ, peroxisome proliferator-activated receptor gamma; ROS, reactive oxygen species.The anti-inflammatory properties of whole grains depend on their unique profiles of bioactive compounds. As shown in Table 1, which compares phenolic acid content and anti-inflammatory effects across common whole grains like oats, quinoa, wheat, barley, and rye, brown rice offers several distinctive advantages. Table 1 - Comparison of free phenolic acid content and anti-inflammatory effects of brown rice with other whole grains. Whole grains Free phenolic acid Anti-inflammatory effects Reference Brown rice Syringic acid, p-hydroxybenzoic acid, sinapic acid, protocatechuic acid ↓ Pro-inflammatory cytokines (TNF-α, IL-6, IL-8, IL-12).↓ Oxidative stress: ↓ MDA, ↑ antioxidant activity in both obese and healthy individuals. [27, 28, 39, 40] Oats Ferulic acid, syringic acid, and sinapic acid ↓ Inflammatory markers (hsCRP, IL-6, IL-8, TNF-α) in individuals with high cholesterol or other health complications. [41, 42] Quinoa Gallic acid, ferulic acid, p-coumaric acid, vanillic acid ↓ Pro-inflammatory cytokines (IL-6, IL-1β, and TNF-α) in vitro and animal models. [43, 44] Wheat Ferulic acid, sinapic acid, p-coumaric acid ↓ Inflammatory markers (CRP, serum amyloid A, IL-8, IL-10) in overweight individuals. [45, 46] Barley Ferulic acid, gallic acid, syringic acid, caffeic acid, chlorogenic acid ↓ Inflammation and ↑ gut health in at-risk individuals, but not in healthy individuals. [47, 48] Rye Ferulic acid, sinapic acid, p-coumaric acid ↓ Specific inflammatory markers (TNF-R2, e-selectin, and endostatin) in men with prostate cancer and ↓ inflammatory cytokines (IL-6, IL-1β) in individuals with metabolic conditions. [49–51] CRP, C-reactive protein; hsCRP, high sensitivity C-reactive protein; IL, interleukin; MDA, malondialdehyde; TNF-α, tumor necrosis factor-α. While most evidence for other grains derives from long-term studies in diseased groups or preclinical models, brown rice uniquely reduces acute postprandial inflammation even in healthy individuals—making it highly applicable for sedentary workers. Unlike commonly milled grains like wheat or rye, brown rice is often consumed whole, preserving its bioactive compounds. Its distinct phenolic acid profile—rich in syringic, p-hydroxybenzoic, sinapic, and protocatechuic acids, unlike the ferulic acid-dominated profiles of others—likely underlies its specific ability to modulate postprandial inflammation. Future perspective Future research should prioritize human trials on brown rice’s time-dependent effects on postprandial inflammation in high-risk groups like sedentary workers, using sensitive novel, multi-faceted biomarkers such as GlycA,[52] transcriptomic[53] or metabolomic profiles,[54] and bile acid,[55] to more accurately quantify the postprandial inflammatory state. Following frameworks like that proposed by Hall et al[10] for standardized postprandial study design will help clarify links between acute dietary responses, chronic low-grade inflammation, and long-term disease risk. Conclusion Sedentary lifestyle and poor diets among office workers contribute to chronic low-grade inflammation. Replacing white rice with brown rice—rich in free phenolic acids—may attenuate postprandial inflammation. Future efforts should employ dedicated human trials—particularly in sedentary populations—to map the time-dependent effect of brown rice on postprandial inflammation, using more sensitive biomarkers to better elucidate its link to long-term disease development.