Background: Postprandial metabolism plays a key role in cardiometabolic health, and its impairment with ageing is associated with increased disease risk. While yoghurt consumption has been linked to improved fasting metabolic markers, its acute postprandial effects are less well understood, particularly in older adults. This study investigated whether yoghurt consumption influences age-related postprandial metabolic dysregulation. Methods: In a randomised crossover design, 14 young (20–35 years) and 14 older (65–80 years) healthy men consumed 600 mL of whole milk or yoghurt following an overnight fast. Biochemical markers (glucose, insulin, triglycerides, TNF-α, IL-6, GIP and ghrelin) were measured at baseline and up to six hours postprandially. Differences in lipid metabolism by age were further investigated by assessing free fatty acid (FFA) responses in the yoghurt phase only. Postprandial responses were analysed for time, age, product and interaction effects, and summarised using incremental area under the curve (iAUC) and incremental maximum concentration (iCmax). Results: Glucose and insulin responses were influenced by product (time × product, p < 0.05), with yoghurt resulting in significantly lower iCmax values compared with milk. In contrast, triglyceride responses were influenced by age (time × age, p < 0.05), with older adults exhibiting higher iAUC and iCmax, delayed peak concentrations and slower return to baseline levels, independently of the product consumed. No significant age × product or age × product × time interactions were observed for any biochemical marker. Among the 37 FFAs quantified in the yoghurt phase, seven – predominantly saturated and abundant in yoghurt – exhibited a significant time × age interaction, accompanied by higher iAUC or iCmax in older adults. Conclusions: Dairy fermentation improved postprandial glucose and insulin responses, whereas ageing predominantly affected lipid dynamics. Fermentation did not attenuate impairments in postprandial triglyceride metabolism in this acute setting. Profiling individual postprandial FFAs may enhance understanding of metabolic flexibility and inform personalised dietary strategies across the lifespan.
