Low-grade inflammation, indicated by elevated inflammatory markers like C-reactive protein (CRP), is a risk factor for various chronic diseases including type 2 diabetes, coronary heart disease, and cancer. A growing body of evidence suggests that whole grain consumption is inversely associated with low-grade inflammation and chronic diseases. However, the association between refined grain intake and inflammation remains inconclusive. Some studies show a negative or neutral relationship, while others suggest an unfavorable impact due to the association with unhealthy dietary patterns. This cross-sectional study examined the relationship between whole and refined grain consumption and serum hs-CRP levels in a population of healthy elderly Finnish men and women from the Kuopio Ischaemic Heart Disease Risk Factor Study (KIHD). The study aimed to elucidate the impact of grain type on low-grade inflammation.

Existing epidemiological studies have shown an inverse association between whole grain intake and low-grade inflammation, as measured by CRP levels. However, the results from randomized controlled trials are conflicting. Similarly, studies on the relationship between refined grain consumption and inflammation have yielded inconsistent findings, with some showing negative or neutral effects, and others suggesting a positive relationship. The inconsistencies might stem from differences in the amount and types of grain products consumed, variations in dietary assessment methods, and differing CRP levels in the study populations. The role of dietary fiber, a component of whole grains, in modulating inflammation is also a focus of research. Some studies suggest an inverse relationship between total dietary fiber and inflammatory markers, including CRP, while others have explored the effects of fiber sources specifically. The potential mediating role of BMI in the association between grain intake and inflammation has also been examined in previous research.

This study used data from the KIHD, a population-based study of cardiovascular disease and other chronic diseases in middle-aged and older adults in eastern Finland. The current analysis included data from 1999-2001 examinations of 756 participants (391 men and 365 women) aged 53–73. Participants with missing data on hs-CRP or dietary intakes, or with hs-CRP > 10 mg/L or elevated blood leucocyte count (indicating acute inflammation) were excluded. Individuals with inflammatory diseases were also excluded. Dietary intakes were assessed using four-day food records (three weekdays and one weekend day), which were cross-checked by a nutritionist. Whole grain intake was defined according to the HEALTHGRAIN definition. Refined grain intake was calculated by subtracting whole grain intake from total grain intake. Serum hs-CRP concentrations were measured using an IMMULITE chemiluminescent immunoassay system. Statistical analyses included ANCOVA and linear regression, controlling for age, gender, energy intake, BMI, smoking, physical activity, education, alcohol consumption, and various dietary factors (fat quality, fruit, vegetable, and berry intake, red meat, dairy, fish, butter, vegetable oil margarine, and egg intake) in different models. Model 4 further adjusted for fiber from grains. Statistical significance of potential interactions according to gender and BMI was assessed using stratified analysis and likelihood ratio tests. Linear trends across quartiles of grain intake were also assessed.

The mean intake of whole grains was 136 g/day (SD 80), and refined grains was 84 g/day (SD 46). Higher whole grain intake was significantly associated with lower hs-CRP concentrations in the initially adjusted models (Model 1). Each 50 g/day increase in whole grain intake was associated with a 0.17 mg/L (95% CI 0.08–0.27 mg/L) lower hs-CRP concentration. However, this association was attenuated after adjusting for lifestyle and dietary factors (Models 2 and 3) and further attenuated after adjusting for fiber from grains (Model 4), becoming non-significant. Higher refined grain intake was associated with higher hs-CRP concentrations in the multivariable-adjusted models (Models 2 and 3). Each 50 g/day increase in refined grain intake was associated with a 0.23 mg/L (95% CI 0.08–0.38 mg/L) higher hs-CRP concentration. This association was slightly attenuated, but remained significant after adjusting for fiber from grains (Model 4). Stratified analyses showed that the inverse association between whole grain intake and hs-CRP was stronger in women (P-interaction = 0.065), while the direct association between refined grain intake and hs-CRP was stronger in men (P-interaction = 0.512), although these interactions were not statistically significant. Fiber intake from grains was associated with lower hs-CRP levels, suggesting that fiber may at least partly explain the association between whole grain intake and hs-CRP.

This study found that higher whole grain intake is associated with lower hs-CRP levels and higher refined grain intake with higher hs-CRP levels in a sample of healthy older adults. This supports the existing evidence of a beneficial effect of whole grains on inflammation. The attenuation of the association between whole grains and hs-CRP after adjustment for fiber intake suggests that the fiber content of whole grains plays a significant role in their anti-inflammatory effect. The findings are consistent with some previous observational studies, but the existing literature is heterogeneous, likely due to variations in methodology and study populations. The study's cross-sectional design limits causal inference. Additional studies are needed to fully understand the mechanisms underlying the relationship between grain products and low-grade inflammation.

This study suggests that higher consumption of whole grains is linked to lower hs-CRP levels, whereas higher consumption of refined grains is associated with higher hs-CRP levels. The high fiber content in whole grains may partly account for the observed association. Future research should investigate the underlying mechanisms and conduct well-designed intervention studies to strengthen the evidence base for dietary guidelines recommending whole grain consumption.

The cross-sectional design prevents causal conclusions. The study's focus on hs-CRP as the sole inflammatory marker limits generalizability. The study population comprised primarily elderly Caucasians from a specific geographic area, potentially limiting the generalizability of the findings. The study's reliance on self-reported dietary intake via food records, while considered a gold standard, is subject to reporting bias. Lastly, the study might not have fully accounted for all potential confounding factors associated with healthy lifestyle and diet choices.