L-Carnitine is small peptide/amino acid that is essential in all animals for the production of energy. Carnitine is needed by the body for the metabolism of fatty acids into energy in the cells. It helps the body utilize fat for conversion into energy while maintaining the lean muscle mass, which helps reduce the overall body fat. It may also help decrease the levels of cholesterol and lipids (fats) in the blood.

Because L-Carnitine is essential in the process of converting fatty acids into energy a deficiency may result in increased fat storage, decreased performance, and, potentially, an increased risk of heart disease. A temporary deficit of L-Carnitine can lead to reduced energy and symptoms of fatigue and slow recovery time or the inability to develop stronger muscle power despite exercise and training.

The natural source of L-Carnitine is fresh meat and milk, however manufactured pet foods frequently contain less than 5% of the L-Carnitine of fresh meat. With the vast majority of pets being fed on manufactured diets, supplies of L-Carnitine in the diet are often insufficient. 

Synthesis in the body occurs mostly in the liver. However skeletal and heart muscles, which use 95-98% of the supplies, cannot synthesise their own L-Carnitine and this explains why deficiency most commonly occurs in these tissues. 

The dog in particular is a species predisposed to a deficiency of L-Carnitine. This is because there is a high level of L-carnitine excretion via the urine and very little re-absorption through the renal tubules.