The relationship between the inflammatory potential of the diet and metabolic syndrome in Black South Africans

Abstract

Introduction and aim: The prevalence of the metabolic syndrome (MetS) is increasing globally. In South Africa it is mainly linked to the high prevalence of obesity, sedentary lifestyles and poor dietary habits, which are now also observed in rural areas. MetS and its components raise major public health concerns due to their strong connection to the pathophysiology of cardiovascular disease (CVD) features. Recent studies suggest that chronic low-grade inflammation, associated with obesity, plays a central role in the development of MetS, and contributes to the development of other metabolic dysfunctions. Several studies have closely linked diet and inflammation; thus dietary inflammatory indices have been developed with the aim to determine the inflammatory potential of whole diets. Since diet influences inflammation and CVDs, and with MetS rising exponentially in South Africa, we aim to investigate whether the dietary inflammatory potential of a Black South African population is associated with blood levels of inflammatory markers and ultimately the MetS. Methods The proposed mini-dissertation is affiliated to the South African arm of the international PURE study (PURE-SA-NW). This study was of cross-sectional design and included 2 010 individuals who participated in the PURE-SA-NW data collection of 2005. The study participants were Tswana-speaking, Black South Africans residing in rural and urban areas of the North-West Province, who were apparently healthy individuals, older than 30 years, and not using any acute or chronic medication in exclusion of blood pressure medication. The dietary intake of the participants was assessed through a validated quantitative food frequency questionnaire, from which the Energy-adjusted Dietary Inflammatory Index (E-DII) was calculated. MetS was diagnosed according to the guidelines of the International Diabetes Federation (IDF). The anthropometrical measurements included weight, height, BMI, hip and waist circumference. The biochemical tests used included inflammatory markers including C-reactive protein (CRP), albumin, interleuken-6 (IL-6), homocysteine (Hcy), fibrinogen, plasminogen activator inhibitor-1 activity (PAI-1act) and others, including glucose and blood lipids. Results The main aim of this study was to compare the inflammatory index of the diet of the PURE-SANW study participants diagnosed with MetS with those without MetS. The literature-based E-DII, as outlined by Shivappa et al. (2014), was utilised to calculate the inflammatory index of the PURE study participants’ diets.

The MetS group comprised of more women compared to the controls, lived mainly in urban areas, and were older than the control group. Individuals with MetS consumed less alcohol and used less tobacco than the control group. There was no statistically significant difference between the mean E-DII of the MetS and control groups. The MetS participants consumed higher amounts of pro-inflammatory as well as antiinflammatory food components than the controls. In men, hypertensive status, fasting glucose, waist circumference and LDL-cholesterole were all significantly higher and HDL-cholesterol significantly lower in the MetS group than in the controls, while in women, WC reached borderline significance only with no significant difference reported for HDL-C. Anthropometric indices as well as inflammatory markers measured were all higher in the MetS group compared to the control group, as expected. The mean E-DII did not differ between individuals with different numbers of MetS components and the number of participants with MetS was evenly distributed across the E-DII quartiles. Regarding the MetS, there were no significant differences observed between the E-DII quartiles for any of the MetS components or MetS itself, even after adjusting for covariates. There was also no significant difference in any of the inflammatory markers investigated across the quartiles before or after adjustment for covariates, except for a borderline significant decrease in albumin, after full adjustment. Conclusion The findings of this study suggest that MetS may be influenced by factors other than the inflammatory potential of the diet in Black South Africans, particularly in this context of limited dietary intakes. Further studies are thus needed to substantiate the inflammatory role of the diet in the development of MetS in Black South Africans. The adoption and maintenance of a healthy lifestyle, however, remains important to reduce chronic disease risk.