If I look back to the studies that are included in the Cochrane Review, the psychosocial measures that are typically assessed are perceived self-efficacy for dietary practices and for physical activities, so they're behaviour-specific.
Other measures include mastery of the general control people perceive in their lives--that work is only starting to come out. Generally, in quotation marks, the “gold standard” for determining whether or not these studies are effective look at some measure of body composition or prevalence of overweight and obesity.