Background: Understanding and measuring diet quality is a topic that has received increasing attention in recent years with the NOVA system being a catalyst for this change in 2009. Recent advances in this area suggest that, at a population level, diets are shifting toward a reliance on hyper-palatable ultra-processed foods (UPFs) across the globe. While the development of UPFs was once strictly about creating convenient, mass-producible foods; with the increasing interest in alternative dietary patterns (ADPs) there is now a milieu of specialty UPFs marketed towards individuals consuming lower-carbohydrate and plant-based diets. Common lower-carbohydrate diets include the ketogenic diet (KD) and low-carbohydrate, healthy fat (LCHF) diet, while the vegan (VEGAN) and vegetarian (VEGE) are common plant-based diets. Despite the growing interest and number of UPFs available for these once-niche groups, little is known about the translation of dietary guidelines into practice and how the availability of UPFs impacts overall diet quality (DQ) in these individuals. This research aimed to explore the DQ of adults adhering to ADPs for at least 6-months using a modified questionnaire and two novel food classification systems.

Methods: In this pilot study, a modified online dietary habits questionnaire was developed and disseminated; results were interpreted using the NOVA (not an acronym) and HISS (Human Interference Scoring System) food classification tools. Participants were recruited via social media platforms between Friday 26th August and Sunday 18th September 2022 and responded to the questionnaire, anonymously, via Qualtrics. Data were quantitatively analysed using descriptive and parametric statistics (oneway repeated measures ANOVA, two-way repeated measures ANOVA and linear regression) in the software programme, JASP (version 0.16.3.0).

Results: There was a total of 168 responses comprising 56 KD (m=16, f=39), 66 LCHF (m=13, f=53), 14 VEGAN (m=4, f=10), and 32 VEGE (m=5, f=27). Respondents were predominantly of European descent, female, and classified as moderate-income professionals. Analysis of DQ revealed that individuals adhering to a lower-carbohydrate diet (either KD or LCHF) tended to consume a smaller proportion (% of total serves) of their diet from UPFs and a larger proportion from unprocessed and minimally processed foods (KD 53 ±12; LCHF 51 ±13). There was a statistically significant difference in NOVA% among the four ADPs F(6.150, 336.184) = 8.285, p < 0.001, with a medium effect size (η²= 0.063). Food groups contributing to intake in NOVA 1 (minimally processed food category) and NOVA 4 (ultra-processed food category) were similar among lower-carbohydrate individuals and plant-based individuals respectively. There was an inverse relationship between perceived and actual DQ, and NOVA and HISS were only similar across the fourth level of processing (UPFs). These data show that diet quality assessment tools can be applied to a range of dietary patterns.

Conclusion: These data indicate that in free-living individuals, DQ (as assessed by the proportion of dietary intake as a number of serves, across different levels of food processing) is higher among those adhering to lower-carbohydrate diets compared to those adhering to plant-based diets. However, these individuals are not exempt from the consumption of UPFs or the belief that their diet quality is superior to what it is. Future research should explore the difference in DQ in larger samples, validate existing tools for the quantification of DQ and assess whether there are safe thresholds for the consumption of UPFs in the context of different dietary patterns.