Among the multifactorial causes of undernutrition in old age, gastrointestinal mucosa altered function and resulting specific malabsorption are the most relevant. Despite numerous studies that have dealt with the effects of aging on the digestive tract of mammals, results showed discrepancies in terms of proliferation and biochemical aging small intestine events. However, the slowing-down of the maturation process and the poor adaptation of metabolism and intestinal function are obvious and there is evidence that protective mechanisms are impaired with age and contribute to affecting the trophic activity and related systemic homeostasis. Good prospects to improve gastrointestinal function in the elderly are essential and research on nutritional intervention to limit and counteract age-related impairments must be extensive. Probiotics are good candidates and fermented milks might be of great interest. In the present study we first show the main structural and functional variations between 3- and 23-month-old rat small intestines. The trophic consequences of aging and nutritional adaptation under basal conditions are also analyzed and discussed after 20 days of a yogurt-supplemented specific diet in both young and aged rats. The main variations that occur with aging and yogurt diet are located in the proximal small intestine. The present findings indicate a slight improvement of morphological trophic parameters in both young and aged rats by yogurt, whereas enzymatic changes are more discrete. Despite the obvious age-related decrease in trophicity, we suggest that assessment of probiotic potentials on trophicity requires a more altered model than normal, healthy aging animals.