As Ryan says, “coffee is coffee is a complex mixture of chemicals” (2005). Caffeine is an effective ergogenic — something that improves athletic performance — it spares muscle glycogen and delays fatigue. For more on caffeine.Coffee also contains phytochemical compounds called chlorogenic acids, an important group of biologically active and antioxidant dietary phenols.
Chlorogenic acids have recently caught the attention of obesity researchers and dietary supplement manufacturers alike, as they can help decrease hunger. Mouse studies to date have produced mixed results, so I wouldn’t run out and buy green coffee bean extract just yet (2,3).