This study aims to determine the effects of different alkaline supplementations on high protein diet-induced abnormalities affecting bone metabolism in rats which were also undergoing physical exercise of moderate intensity. Sixty elderly Sprague-Dawley rats were randomly divided into four groups of 10 rats each and treated for 16 weeks as follows: baseline control group fed normal food (C); acidic high-protein diet supplemented group (chronic acidosis, CA group), bicarbonate-based alkaline formula (Basenpulver, Named, Italy) supplemented chronic acidosis (BB-CA) and citrate-based alkaline supplement (CB-CA). Throughout the supplementation period, rats were put on a treadmill training mimicking a moderate level of exercise. In the CA group, 24-hour urinary calcium (Ca) and phosphorus (P) excretion were increased over 30 percent (p<0.05 vs normal diet controls). However serum Ca was not significantly changed. Femural and tibial BMD and BMC was significantly decreased in the CA group (p<0.05) but both alkaline supplementations prevented such phenomenon (p<0.05 vs CA), without significant difference between the two formulations although the BB-CA group showed significantly more preserved trabecular bone volume (p<0.05 vs CB-CA group). An increased level of over 50 percent of urinary Dpd observed in the CA group (p<0.001) was reverted to normal by both supplementations (p<0.001 vs CA group). The same applied to urinary net acid excretion (p<001) with BB-supplementation performing better than CB-supplementation (p<0.05). Moreover, while the latter did not modify Nterminal telopeptide value, BB-supplementation significantly normalized this parameter (p<0.05 vs CA group) which exercise and acidic protein diet had modified (p<0.01 vs control diet). Overall, the present study shows that a bicarbonate-based alkaline formula, when administered to a dose amenable to clinical use, may significantly protect bone structure in exercising aged animals to a greater extent than a quali/quantitavely similar citrate-based formula.