Model Indices were satisfactory: RMSEA (Root Mean Square Error of Approximation) = 0.023; CI (confidence interval) = 0.022 0.025; CFI (Comparative Fit Index) = 0.963; TLI (Tucker-Lewis Index) = 0.959; SRMR (Standardized Root Mean Square Residual) = 0.045. R Squares indicated the model explained 48% of variance in Physical Wellbeing, 15.9% of Psychological Wellbeing, 16.8% of Moods and Emotions, 28.3% of Self-Perception, 8.4% of Autonomy, 8.4% of Parental Relationships and Home Life, 6.1% of Financial Resources, 11.2% of Social Support and Peers and 15.1% of School Environment.

Direct and indirect relationships between Sex, physical activity, social media use, alcohol abstinence, food choice factors and health-related quality of lifePhysical wellbeing

Higher scores on physical wellbeing were directly associated with greater physical activity, greater alcohol abstinence, and more frequent intake of the bread/dairy food choice factor (Table 2).

Table 2 Direct effects of HRQoL on (a) exogenous measures (b) food choice factors (mediated measures) and (c) exogenous measures on food choice factors

In terms of the model, physical activity was indirectly related to physical wellbeing via more frequent choice of the bread/dairy food choice factor (est = 0.015, se = 0.006, t = 2.349, p = 0.019).

Psychological wellbeing

Higher scores on psychological wellbeing were directly associated with being male, greater physical activity, less use of social media, greater alcohol abstinence, more frequent intake of meat and less frequent intake of the protein factor (Table 2).

The relationship between higher psychological wellbeing and being male was mediated by more frequent intake of meat (est = 0.033, se = 0.016, est/se = 2.055, p = 0.040). More frequent intake of meat was also a mediating factor between less use of social media and higher psychological wellbeing (est = 0.009, se = 0.004, est/se = 2.106, p = 0.035). The mediating effect of a less frequent intake of protein reduced the strength of the association between physical activity and psychological wellbeing (est=-0.029, se = 0.014, est/se=-2.149, p = 0.032).

Moods and emotion

Higher moods and emotion scores were directly associated with being male, greater physical activity, greater alcohol abstinence, less social media, less frequent intake of the junk food factor, less frequent protein, more frequent meat intake and more frequent intake of fruit and vegetables (Table 2).

The relationship between higher moods and emotion and being male was mediated by less frequent intake of junk food (est=-0.029, se = 0.015, est/se=-1.998, p = 0.046), less frequent intake of fruit and vegetables (est=-0.058, se = 0.024, est/se=-2.411, p = 0.016) and more frequent intake of meat (est = 0.038, se = 0.016, est/se = 2.419, p = 0.016).

Greater physical activity was associated with a higher moods and emotion and this was mediated by more frequent intake of fruit and vegetables (est = 0.047, se = 0.018, est/se = 2.635, p = 0.008) and less frequent intake of the protein factor (est=-0.054, se = 0.015, est/se=-3.676, p = 0.000).

Less use of social media and higher moods and emotion was mediated by more frequent intake of the meat factor (est = 0.011, se = 0.004, est/se = 2.594, p = 0.009) and less frequent intake of fruit and vegetables (est=-0.004, se = 0.002, est/se=-2.092, p = 0.036).

The direct association between alcohol abstinence (greater) and higher moods and emotion was mediated by less frequent intake of the protein factor (est=-0.027; se = 0.012; est/se=-2.223; p = 0.026).

Self-perception

Higher self-perception scores were directly associated with being female, greater physical activity, less social media, greater alcohol abstinence, and less frequent intake of the protein factor (Table 2).

The association between higher self-perception and greater physical activity was mediated by less frequent consumption of protein (est=-0.051, se = 0.020, est/se=-2.599, p = 0.009) and more frequent intake of meat (est=-0.025, se = 0.013, est/se=-1.974, p = 0.048).

Autonomy

Higher scores on Autonomy were directly associated with being female and greater physical activity (Table 2). The autonomy scores were neither directly nor indirectly associated with any of the food choice factors.

Parental relations and home life

Higher scores on parental relations and home life were directly associated with being male, greater physical activity, less social media use, greater alcohol abstinence, less frequent consumption of protein and more frequent intake of fruit and vegetables (Table 2).

The higher scores on parental relations and home life in males was mediated by less frequent consumption of fruit and vegetables (est=-0.065, se = 0.029, est/se=-2.264, p = 0.024).

The association between higher scores on parental relations and home life and greater physical activity was mediated by less frequent intake of the protein factor (est=-0.049, se = 0.018, est/se=-2.799, p = 0.005) and by more frequent intake of the fruit and vegetables factor (est = 0.053, se = 0.022, est/se = 2.409, p = 0.016).

Greater alcohol abstinence and higher parental relations and home life was mediated by less frequent intake of protein (est=-0.024, se = 0.011, est/se=-2.309, p = 0.021).

Financial resources

Higher scores on financial resources were directly associated with greater physical activity, less frequent consumption of protein and more frequent intake of fruit and vegetables (Table 2).

Although there was no direct association between sex and financial resources, those more frequently consuming fruit and vegetables were more likely to be female and to have higher financial resources (est=-0.089; se = 0.035; est/se=-2.558; p = 0.011).

Higher financial resources and greater physical activity was mediated by less frequent intake of protein (est=-0.053, se = 0.019, est/se=-2.747, p = 0.006) and more frequent intake of fruit and vegetables (est = 0.072, se = 0.029, est/se = 2.516, p = 0.012).

The association between social media use and financial resources was mediated by less frequent intake of the fruit and vegetables (est=-0.007, se = 0.003, est/se=-1.982, p = 0.047).

Although there was no direct association between alcohol abstinence and financial resources, lower alcohol abstinence was associated with less frequent intake of protein and a lower financial resources score (est=-0.026, se = 0.013, est/se=-2.024, p = 0.043).

Social support and peers

Higher scores on social support and peers were directly associated with being female, greater physical activity, greater social media use, more frequent consumption of protein and more frequent intake of fruit and vegetables (Table 2).

The association between being female on social support and peers was mediated by less frequent intake of fruit and vegetables (est=-0.068, se = 0.028, est/se=-2.402, p = 0.016).

The association between higher social support and peers and greater physical activity was mediated by (a) less frequent intake of protein (est=-0.041, se = 0.014, est/se=-2.948, p = 0.003) and (b) more frequent intake of fruit and vegetables (est = 0.055, se = 0.022, est/se = 2.542, p = 0.011).

Higher social support and peers scores and the association with greater use of social media was mediated by less frequent intake of the fruit and vegetables (est=-0.005, se = 0.003, est/se=-1.977, p = 0.048).

While there was no direct association between protein on social support and peers, the association between alcohol abstinence and higher social support and peers was mediated by less frequent intake of protein (est=-0.020, se = 0.010, est/se=-2.084, p = 0.037).

School environment

Higher scores on school environment were directly associated with greater physical activity, less social media use and greater alcohol abstinence (Table 2). School environment was unrelated to sex or to food choice factors. There were no indirect relationships between the food choice factors and school environment.

Food choice factors, sex, physical activity, Social Media Use and Alcohol abstinence (partial regression coefficients)

More frequent intake of the Junk food factor was directly associated with being male, less physical activity, greater social media use and lower alcohol abstinence. Frequent intake of the Meat factor was directly associated with being male and greater social media use. Frequent intake of the Protein factor was directly associated with greater physical activity and lower alcohol abstinence. Frequent intake of the Fruit and Vegetable factor was directly associated with being female, greater physical activity and less social media use. More frequent intake of the Bread/Dairy factor was directly associated with greater physical activity.