L-Carnitine Supplementation in Overweight Dogs: An Uncontrolled Pilot Study on Nutrient Digestibility, Metabolic Health, and Body Condition

Background: L-carnitine supports mitochondrial fatty acid transport and has been proposed for weight management, but its short-term effects in overweight dogs are unclear. This pilot study aimed to generate preliminary, hypothesis-generating data on these effects, including possible dose–response patterns, to inform the design of a future randomized, placebo-controlled trial. Methods: Twenty-one Golden Retriever dogs (8–10 years) were assigned to three groups of seven: a control diet group (BCS < 7) receiving no supplementation, receiving no supplementation, and two overweight groups (BCS ≥ 7) receiving 1 g/day or 2 g/day oral L-carnitine for 30 days. Digestibility, faecal dry matter and consistency, BCS, body weight, appetite (4-day monadic feeding test), and serum biochemical, endocrinological and oxidative-status parameters were assessed. Results: BCS, as assessed by a blinded investigator, decreased from baseline at both doses (p < 0.05), more markedly at 2 g/day; however, body weight remained unchanged throughout the study period. Food intake during the post-supplementation appetite test was lower at 2 g/day than in the healthy reference group (p < 0.05), though no pre-supplementation baseline appetite measurement was available for comparison. Serum cholesterol decreased and total antioxidant status (TAS) increased at both doses by day 30 (p < 0.05); however, HDL also decreased at both doses and triglycerides increased at 2 g/day, indicating that lipid profile changes were not uniformly favourable. Insulin decreased at both doses, and visfatin decreased significantly at 2 g/day (p < 0.05). No significant changes in digestibility were observed. Conclusions: In this uncontrolled pilot study, short-term L-carnitine supplementation was associated with dose-related within-group changes in selected metabolic indicators in overweight dogs, without measurable weight loss within 30 days. Notably, the absence of uniformly favourable lipid profile changes and the lack of an untreated overweight control group limit interpretation. These findings should be regarded as hypothesis-generating and support the rationale for a future placebo-controlled trial, rather than establishing a definitive treatment effect, before L-carnitine can be recommended as an adjunct to longer-term canine obesity-management strategies.