Inter-Individual Variability in Early Postprandial Thermogenesis Following a Standardized Liquid Meal

Diet-induced thermogenesis (DIT) represents the increase in energy expenditure above resting levels following food intake and reflects the energetic costs of digestion, absorption, transport, and metabolism of nutrients. Although DIT typically accounts for a relatively small proportion of total daily energy expenditure, it plays an important role in postprandial metabolism and may contribute to inter-individual differences in energy balance and body weight regulation.

Most prior research has focused on estimating total DIT over prolonged postprandial periods (e.g., 4-6 hours or longer). However, these approaches may obscure meaningful variability in the early phase of the thermogenic response, which is characterized by rapid and dynamic metabolic changes. The most pronounced increase in energy expenditure typically occurs within the first 1-3 hours following meal ingestion, driven by early physiological processes including gastrointestinal activity and neuroendocrine responses.

Emerging evidence suggests that individuals vary substantially in their metabolic response to a standardized meal, even under controlled conditions. However, this variability is often averaged out in group-level analyses or diluted by long measurement windows. The present study is specifically designed to characterize observed inter-individual variability in early DIT, rather than to estimate total thermogenesis or test intervention effects.

This study is a controlled, cross-sectional physiological study in healthy adults. Each participant will complete a single study visit under standardized laboratory conditions. After an initial resting period, resting metabolic rate will be measured using indirect calorimetry. Participants will then consume a standardized liquid meal providing 550 kcal, after which energy expenditure will be continuously monitored for 180 minutes.

Strict pre-test standardization procedures (including fasting, avoidance of exercise, caffeine, and alcohol) will be implemented to minimize non-biological variability. Body composition will also be assessed to support interpretation of metabolic responses.