Green Fast Diet Keto contains one of the most popular weight loss ingredients in history: caffeine. Each two capsule serving contains approximately the same amount of caffeine as one half cup of coffee. Caffeine is a stimulant that induces thermogenesis (fat burning) within your body. It boosts energy and helps you physically burn more fat. It’s backed by more science than BHB ketones, and many people take caffeine daily for weight loss.