Relationship of the dietary phytochemical index to weight gain, oxidative stress and inflammation in overweight young adults

Background: Phytochemicals are bioactive nutrients that help reduce disease risk. A high intake of these compounds is important for optimal health and prevention of disease, but quantification of these nutrients in vivo is costly and time consuming. The present examined whether an alternative, simple 'phytochemical index' (PI) ratio calculation (PI = the ratio of the energy from high-nutrient phytochemical-rich foods to overall daily energy consumed [kJ phytochemical rich foods/total kJ consumed]) was related to several precursors of future disease: annual weight gain, adiposity, oxidative stress and inflammation. Methods: This was a cross-sectional, quantitative, descriptive study (n = 54, age range 18-30 years). Participants were stratified into normal weight and overweight groups. Three-day dietary records were analysed for food items, food groups, energy and the PI score at repeated time points. Blood plasma samples were analysed by colorimetric or an enzyme-linked immunoabsorbent assay for cholesterol subfractions, glycated haemoglobin, total antioxidant status, lipid hydroperoxides, cytokines (interleukins-1 beta and -6) and C-reactive protein). Results: PI values were higher in the overweight-obese group. Correlation values between the PI score and body mass index, waist circumference, waist-to-hip ratio and plasma oxidative stress were significant. The PI score did not correlate with any cytokine levels. The PI score was a significant contributor to yearly weight gain. Conclusions: The PI is inversely related to adiposity and oxidative stress in healthy young adults, and is responsive to body weight changes. This simple, easy to administer index might be useful as a dietary target for appropriate proportion consumption of nutrient-rich foods in weight reduction or management programmes.