The most favoured substrate of the cellular respiration is called glucose which on complete oxidation yields ATP.
The substrate level of phosphorylation is the formation of the ATP molecules from a phosphorylated intermediate and the ADP.
During glycolysis, the substrate-level phosphorylation produces 4 ATP molecules out of which 2 molecules are utilized during the process itself thus there is a net gain of glycolysis produces 2 ATP molecules.
One of the benefits of a vegetarian diet is a reduction in your impact on the environment. Animals store only a small fraction of the energy they extract from the food they eat, and the rest is wasted as heat.