Thirty-two observational studies were included in the review but only 12 were included in the meta-analysis (207,226 participants). The studies in the meta-analysis were reported to be of satisfactory quality.
The meta-analysis reported a significant impact of weight loss advice on efforts at weight loss (OR 3.85, 95% CI 2.71 to 5.49; 12 studies). However there was significant statistical heterogeneity for this analysis (Ι²=98.76%). The results of the sensitivity analyses were similar to the overall analysis. The moderator analyses reported a greater effect of weight loss advice in adults versus children and in patients who were surveyed by telephone compared to those surveyed in person. There were no significant differences in the effectiveness of advice in studies using obese patients only versus mixed samples.
The narrative synthesis reported significant actual weight loss by patients associated with primary care provided advice (seven studies). Other narrative results relating to patient stage of change, patient weight maintenance attempt and specific behaviour changes were reported.