Nordic diet, similar to Mediterranean diet, may also have anti-inflammatory effects
Nordic Diet and Inflammation—A Review of Observational and Intervention Studies
A narrative review of studies evaluating the effects of consuming a Healthy Nordic Diet (HND) suggests that this dietary pattern may have beneficial effects on low-grade inflammation (LGI), although the available evidence is limited. The HND largely overlaps with the Mediterranean diet (MD), in that they both emphasize abundant use of fruits and vegetables, whole grain products, fish, and vegetable oil, and restrict the use of saturated fat (milk fat) and red and processed meat. Differences lie in that HND also included local berries, and that HND used mostly canola oil, as opposed to olive oil in MD.
LGI has been linked to the pathogenesis of chronic diseases such as CVD, T2DM, certain cancers and neurodegenerative diseases. Changes in gut microbiota can contribute to LGI, and specifically abdominal obesity (accumulation of visceral fat) is associated with LGI. Weight loss is indeed the main therapy for LGI in overweight and obese people, as it normalizes levels of pro- and anti-inflammatory markers. Specific dietary patterns, such as MD, can also affect levels of inflammatory markers, regardless of weight loss.
The current narrative review considered studies that investigated effects of HND on markers of LGI (CRP, hsCRP, IL-6, IL-1 Ra, leptin, high-molecular weight (HMW) adiponectin, TNF-, IL-1, IL-10, TNF RII, and Cathepsin S.). Data from three observational studies and eight publications about four different interventions (SYSDIET, New Nordic Diet (NND), NORDIET and SYSDIMET) were used.
Observational data consistently showed that high adherence to HND lowers the risk of LGI, as demonstrated by an inverse association between HND and hsCRP. One study also showed an inverse association between HMW-adiponectin and adherence to HND, while other inflammatory markers were not significantly related to the dietary pattern.
Three randomized intervention studies evaluated the effect of HND on LGI, and other studies looked into the effect of selected key components. Studies on combinations of key components of the HND point towards a beneficial effect on CRP levels in subjects with characteristics of metabolic syndrome or healthy overweight.
Of the HND pattern RCT’s, one compared the NND with Average Danish Diet (ADD) in adults with central obesity and components of the metabolic syndrome. Plasma CRP decreased in the NND group. This result was maintained after correction for weight loss, but the benefits did not last during the follow-up of the study. Higher compliance with NND after an active intervention was, however, associated with less weight regain. Another study compared a Nordic prudent with a habitual diet in normal to slightly overweight hyperlipidemic persons. No differences in CRP levels were seen between groups. The observation that cathepsin S was decreased after the HND, did not hold after adjustment for change in body weight and LDL-c level. The third RCT randomized individuals with characteristics of metabolic syndrome and impaired fasting glucose/glucose tolerance to an HND or control group (isocaloric diets). Participants in the HND group showed an improved lipid profile and beneficial changes in lipids and blood pressure were seen in the participants most compliant to HND. IL-1Ra, a sensitive marker of insulin resistance, was the only marker that showed a different response between diets: it was stable in the HND group and increased in the control group.
Other studies have also demonstrated down-regulation of immune response-related genes in adipose tissues and peripheral blood mononuclear cells (PBMC’s) and a potential role of dietary fiber in the regulation of glucose metabolism and LGI.
The reviewed data suggest that the HND may have anti-inflammatory effects. Observed effects varied among studies, because the tested diet was not the same in all studies. Due to the limited amount of available data, it is not possible to draw definite conclusions on anti-inflammatory effects of HND as yet. It is, however, interesting to study this in more detail, as it has proven difficult to adhere to the Mediterranean diet in other parts of the Western world. It may help to consider local food culture in health promoting food patterns.