Effect of diet on blood viscosity in healthy humans: a systematic review

BACKGROUND: Increased whole blood viscosity is associated with increased risk of morbidity and mortality of several life-threatening diseases, including cardiovascular and cerebrovascular disease. The effect of diet on human health has been indicated in many studies, and a health dietary pattern can reduce the incidence of several chronic diseases. OBJECTIVE: The aim of this systematic review was to assess the effect of diet on blood viscosity and related parameters such as haematocrit (HCT). METHODS: This systematic review was carried out in 2017. MEDLINE, Embase, Scopus, Web of Science, and the Cochrane Central Register of Controlled Trials were searched from inception to 2 May 2017. We selected and included randomized clinical trials (RCTs) in the study. The inclusion criteria were articles that describe the effect of any types of local and traditional diet on blood viscosity in apparently healthy individuals. RESULTS: Three randomized controlled trials were included in this systematic review. Different diets were used in the included trials. In one study, ingested dried–bonito broth (DBB) for four weeks, significantly reduced the blood passage time in the intervention group from 55.4±3.4 to 47.6±2.0 sec (mean ± SEM, p<0.05) compared with no significant change in the placebo group. Another study has shown significantly increased blood fluidity score in a vegetarian group in contrast to the control group after six weeks. In the last study, plasma viscosity was significantly decreased in a group which used onion–olive-oil capsules compared to the placebo group, with a highly significant difference between the two groups (p=0.0015). CONCLUSIONS: Our components of food diets may decrease blood viscosity in health status. Better and expanded methodology may improve our results.