Dietary nutrient density and body fat percentage

Background: The intake of nutrient-dense foods is recommended for overall health improvement and maintaining healthy body fat. However, there is a dearth of evidence on the relationship between the dietary nutrient density and body fat percentage. Investigating this relationship depends on the availability of valid dietary assessment methods for estimating micronutrients and the bioavailability of micronutrients, considering that nutrient-dense foods are rich in phytate which may affect the bioavailability of micronutrients. Aims: This thesis primarily investigated the association between change in dietary nutrient density and change in body fat percentage using a prospective cohort study design. It also validated a 4-day food photography method for estimating micronutrients in the diet and conducted a systematic review on the influence of dietary phytates on the bioavailability of micronutrients. Methods: This research was conducted in three stages. Firstly, a 4-day food photography method was validated against the weighed food record method as a reference. Secondly, a systematic review was conducted on the influence of dietary phytate on the bioavailability of micronutrients. Finally, the association between change in dietary nutrient density and change in body fat was investigated in a 6-month prospective cohort study involving 108 adults. For the validation study, measures obtained from both methods were compared using Student’s t-test, and the agreement between both measures was assessed using Bland-Altman analysis. In the systematic review, specific databases were searched, and the results were reported based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) Statement. The relationship between dietary nutrient density and body fat percentage was investigated using linear mixed model regression. For all stages, the statistical significance was considered for p-values less than 0.05. Results: In the validation study, the difference between the measures obtained by the food photography method and the weighed food record was not statistically significant (p> 0.05). Bland-Altman plots showed a good agreement for the nutrient estimates obtained by both methods. The bias for each nutrient estimate was less than 20%. The systematic review concluded that phytate negatively influenced the bioavailability of iron, magnesium and, zinc. In the cohort study, an increase in the dietary nutrient density of vitamins A, E, K and C, folate, iron, calcium, magnesium, potassium, selenium, zinc and, phosphorus were each found to correspond to a decrease in body fat percentage (p< 0.05) after adjusting for dietary phytate and covariates. Conclusions: The food photography method is suitable for assessing dietary micronutrients; dietary phytate reduces the bioavailability of iron, magnesium and, zinc; an increase in dietary nutrient density of vitamins A, C, E and K, folate, iron, calcium, magnesium, selenium and phosphorus was associated with a decrease in body fat percentage in adults.