Interindividual variability in appetitive sensations and relationships between appetitive sensations and energy intake

Weight gain results from sustained positive energy balance, with appetitive sensations (AS) considered key drivers of energy intake (EI). While short-term inter-individual variability in AS is known, the long-term stability and dietary implications remain unclear. This study aimed to rigorously explore daily AS ratings over 17 weeks to determine their stability and the magnitude of inter-individual differences. The hypothesis was that marked and reliable individual differences exist. The second aim was to investigate the directionality of the relationships between AS and eating patterns, and between AS and EI. Conflicting literature exists regarding the influence of individual characteristics (BMI, age, sex) on appetite-diet associations. Thus, the third aim was to examine whether these characteristics consistently map onto AS intensity over time.

Previous shorter-term studies with limited sample sizes suggested reliable inter-individual differences in AS. However, the long-term stability of these ratings and their implications for dietary patterns and EI were not well-characterized. Several hypotheses exist linking AS to adiposity, including the possibility that high chronic hunger or low chronic fullness lead to increased energy consumption, or conversely, that these sensations are a consequence of low EI. The literature on the relationship between AS and individual characteristics such as BMI, age, and sex is mixed, with inconsistent findings regarding their influence on appetite-diet associations and obesity risk.

This 17-week observational study enrolled 97 healthy adults (90 completers, 7 partial completers) aged 18–64 years, with stable body weight and not taking appetite-affecting medications. Participants completed appetite lexicon training and then provided hourly self-reported ratings of hunger, fullness, and thirst on three randomly selected days (two weekdays and one weekend day) at weeks 1, 9, and 17 using a visual analog scale (VAS). Physical activity was assessed using a mobile app (ActivityTracker Pedometer), and 24-h dietary intake was assessed using the ASA24 system. Data analysis included one-way ANOVA to examine within and between individual variances, Pearson's and Spearman's correlations to assess relationships between AS and EI/eating patterns, generalized regression models, linear mixed models, cross-correlation function (CCF) analysis, and path analysis using structural equation modeling (SEM). Statistical significance was set at p < 0.05.

Marked and stable inter-individual differences were observed for hunger, fullness, and thirst across the 17 weeks (e.g., week 1 vs. week 9 correlation for hunger: r = 0.72, p < 0.001). Daily mean variances between individuals were significantly greater than within-individual variances. There were no significant differences in daily mean AS between weekdays and weekends, nor were there significant seasonal effects. The correlation between daily mean hunger and fullness was weak, while hunger and thirst showed a moderate correlation. EI was not statistically different across tertiles of hunger, fullness, or thirst, even after adjusting for age, sex, BMI, and physical activity. CCF analysis indicated that EI more strongly influenced AS than vice versa, with EI 1 hour prior showing significant associations with changes in AS. Path analysis revealed weak, but significant, effects of daily EI on daily mean hunger ratings, but not on fullness or thirst. There were weak, non-significant correlations between AS and eating frequency/portion size. No robust differences in AS were observed across BMI categories, sex, or age groups.

This study provides strong evidence for marked and consistent inter-individual differences in hunger, fullness, and thirst sensations over a prolonged period. Contrary to common assumptions, the findings suggest a weak association between AS and EI under conditions of relative energy balance. The observed asymmetry in the relationship, with EI exerting a stronger influence on AS than vice versa, challenges the notion that AS are primary drivers of EI. This might explain the difficulties in utilizing AS modulation for effective weight management. The weak or non-significant associations between AS and individual characteristics (BMI, age, sex), eating frequency, and portion size align with much of the existing literature.

This study demonstrates the substantial and stable inter-individual variability in hunger, fullness, and thirst sensations. The weak relationship between AS and EI suggests their limited role in predicting energy intake under relatively stable energy balance conditions. Further research is needed to explore whether these relationships differ under conditions of extreme energy imbalance. Future studies could also investigate the role of other AS (desire to eat, prospective consumption) and explore factors that drive the consistent individual differences observed in this study.

This study did not measure desire to eat and prospective consumption, which are also known to influence intake. As an observational study, unmeasured confounding factors may have influenced appetite ratings. Misreporting of energy intake, a common issue in free-living studies, might have weakened the associations between appetitive sensations and EI.