Companies that advertise diet and weight-loss products are well-known for using false or biased advertising. These companies are biased in the sense that they present images of beauty that are subjective as if they were objectively admirable. Moreover, they can play on people's insecurities due to a bias of what a person should ideally be like. It is very important, when dealing with these type of companies, to use skepticism when examining their data. It is very likely that the data has been modified in order to provide a very positive view of the effectiveness of their products. Moreover, it is important to look at their health claims, and not just at their weight-loss claims.
I hope this helps!!