There is about a century of research showing that the most common outcome will be that people lose weight short-term and then regain it long-term as their bodies adjust to food restriction and change physiologically in order to become weight maintaining, weight regaining machines. Then there is deeply flawed research (often funded and/or conducted by the weight loss industry) that uses a number of methods to try to obfuscate the abject failure of these weight loss interventions.
In all of this, there is a question that is almost never even asked, certainly not by the weight loss industry:
Are the people following these weight loss interventions getting enough actual nutrition?