The presence of food processing techniques has expanded rapidly over the last two decades with the intake of ultra-processed foods increasing subsequently. Nutrition epidemiology research demonstrates the implications of food processing levels and ultra-processed food intake on health outcomes including the increased risk of obesity, type 2 diabetes, and cardiovascular disease. Currently, existing assessment and appraisal tools for overall quality of dietary intakes face significant gaps. Firstly, traditional diet quality indices based on food groups or nutrient density fail to differentiate between untouched and processed foods, and as a result, likely contribute to the misclassification of healthy items as the extent of food processing is often not considered. Secondly, current food classification systems that classify intakes based on food processing, lack an established quantitative measure that employs recommended dietary serving sizes to quantify the levels of intake respective to the classifications of intake.

This research investigates the relationship between assessing dietary quality and existing diet quality indices and food classification systems in two distinct chapters. Firstly, an extensive narrative review of diet quality indices and food classification systems highlights the variation between assessment measures seeking the same outcome of overall diet quality. Specifically, it evaluates the extent of diet quality assessment and the formulation of assessment tools. Secondly, five hypothetical meal plans were analysed for diet quality using four established diet quality indices along with the Human Interference Scoring System (HISS), a diet quality tool recently developed by the Human Potential Centre nutrition staff. The HISS aims to classify dietary intake based on food processing levels and quantify overall diet quality via proportionate servings of unprocessed and processed foods. The classification system is based off the well-known NOVA system with some key modifications to the categories and classifications.

In Chapter One, an extensive narrative review of existing diet quality indices and food classification systems reveals several key areas of concern, including the variance in the construction and composition of diet quality assessment tools and the resulting implications. In Chapter Two, an exploratory analysis shows positive correlations between diet quality indices across each of the meal plans, albeit varying strengths. The analysis of dietary intakes supports the oversimplistic and reductionist flaws of existing diet quality indices, while simultaneously demonstrating the HISS can provide a simple, yet comprehensive dietary appraisal tool.

To conclude, diet quality indices are useful assessment tools to appraise dietary quality given the appropriate population and settings. The HISS presents a food classification system with the ability to classify dietary intake according to food processing levels and quantify the overall diet quality via the total servings of unprocessed and processed foods. As a result, the HISS provides researchers and health professionals with a simple dietary appraisal tool that allows for straightforward translation of dietary analysis messages. Future research may consider further testing of the HISS with a larger sample size to test for the reliability and validity of the system and increase the generalisability of the results.