Old-age dogs may get an advantage from eating food with fewer calories and less fat. According to researchers, L-carnitine, a vitamin-like compound made from amino acids found in red meats, chicken, fish, and dairy products, may help the body use fat for energy. The reason is, seniors and geriatrics need lower-calorie diets to help prevent obesity -- a huge problem in seniors -- and higher-fiber diets to improve gastrointestinal health.