The short answer: absolutely none!
The long answer requires a bit of a background. In October 1994, the Dietary Supplement Health and Education Act was signed into law by President Clinton. After this law was in place, manufacturers of dietary supplements did not need approval from the FDA to begin marketing and selling their supplement products.
This is in direct contrast to pharmaceutical drugs which need to prove that they are both safe and effective before they can be brought to market.
Following are some of the problems that this law created:1) Nobody is checking up on the ingredients in these supplements. Often they don’t contain what they say they do, or contain little to none of the advertised active ingredients.
2) For the same reason, sometimes they contain harmful ingredients like pharmaceutical drugs or even banned substances. There is really no regulation until there is a report of illness or injury, then the FDA will look into it. It is up to the FDA to prove that these substances are not safe and they don’t have the resources to test all of the tens of thousands of products on the market.
3) They never stand up to scientific scrutiny. I read the nutrition literature every month, and whenever an independent university or research institution tests these weight loss supplements, they don’t increase weight loss when compared to a placebo in well-designed randomized controlled trials.
Stay away from weight loss supplements. At best they are ineffective, at worst they can make you sick. If weight loss is your goal, there is no substitute for a good diet, the right cardiovascular exercise program and a well-designed strength training routine.