FIRST: By inhibiting ATP citrate lyase, HCA might inhibit the supply of fuels that go to make fatty acids and cholesterol; i.e. it "inhibits fat production". This action specifically inhibits the conversion of carbohydrate to fat, even though the extent to which this actually happens in the body is questionable.
SECOND: There is preliminary evidence that HCA, by inhibiting malonyl CoA, can promote fatty acid oxidation, or the rate at which fats are made available to meet energy (calorie) requirements.
THIRD: HCA might also promote glycogen synthesis in the liver and possibly in other tissues -- obviously a beneficial action for athletes by increasing the available energy during workouts.
FOURTH: There is suggestive evidence that HCA can promote serotonin synthesis in the brain. If it really does, then HCA would be very useful for controlling carb cravings -- since that is what serotonin unquestionably does.
"these results do not support the hypothesis that HCA alters the short-term rate of fat oxidation in the fasting state during rest or moderate exercise, with doses likely to be achieved in humans while subjects maintain a typical Western diet (approx 30-35% total calories as fat)."