Calorie-blockers are compounds that prevent the intestinal uptake of either fatty acids or carbohydrates.
These typically work by either acting on the Pancreas (organ) to prevent the release of fat and carbohydrate digesting enzymes (such as lipase and amylase), or to physically bind to either the enzyme after release or the substrate itself and prevent the enzyme from exerting it's effects on said substrate.
Calorie-blockers are typically used to alleviate the caloric load of a cheat meal, although fat-blockers are sometimes used to prevent the uptake of fat-soluble toxins in foods where one aims to absorb a water soluble compound (as is the case with Cinnamon).
Fat-Blocker, Carb-Blocker, Starch-Blocker, Fat-Blockers, Lipase Inhibitors, Amylase Inhibitors
Fat-blockers should not be taken in situations where one can benefit from the fatty acid being absorbed, as is the case of Fish Oil supplementation.
Overusage of calorie-blockers may result in loose stool, as that stuff has to leave your body somehow and fatty acids (especially) make good colonic lubricant.Examine.com Medical Disclaimer
Calorie-Blockers are never 100%.
Do not think that you can take some green tea and kidney bean extract before a meal, binge, and then continue to lose weight. If anything that will just make you fat and give you very loose stool.
They can make good finishing touches to a diet plan, but should never be the primary focus.
Scientific support for each compound can be found vicariously through their respective pages.