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Obesity – may improve mortality

Evidence Summary: 

We found one systematic review by Ma et al., assessing the role of weight loss interventions in reducing all-cause mortality, cancer mortality and cardiovascular mortality (1). The review identified 54 suitable randomised-control trials to include with a total of 30,206 patients. Of these trials, 53 included low-fat diets, 22 provided exercise programmes and 29 provided exercise-advice only. The patients were followed-up for a period of at least one year. Quality of evidence was judged using the GRADE approach. High quality evidence from 34 trials (21,699 participants) demonstrated a decrease in all-cause mortality (risk ratio 0.82, 95%CI 0.71-0.95). Evidence from 8 trials demonstrating the effect of physical activity on cancer mortality was graded as very low quality resulting in uncertainty in the effect(2). Further, the study was not adequately powered to comment on the effect of physical activity on mortality in separation to diet.  

Quality of Evidence: 

Grade C – Consistent evidence from multiple RCTs in all domains investigated 

Strength of Recommendation: 

Grade 2 – Unknown effect, low risk of physical activity  


There are no systematic reviews investigating the effect of physical activity on mortality in overweight or obese patients. However the evidence amongst the general population of a mortality benefit of physical activity is strong, and therefore physical activity may be advised to this patient cohort as a way of likely reducing mortality. 


  1. Ma C, Avenell A, Bolland M, Hudson J, Stewart F, Robertson C, Sharma P, Fraser C, MacLennan G. Effects of weight loss interventions for adults who are obese on mortality, cardiovascular disease, and cancer: systematic review and meta-analysis. BMJ. 2017 Nov 14;359:j4849. doi: 10.1136/bmj.j4849. PMID: 29138133; PMCID: PMC5682593. 
  2. Ekelund U, Dalene KE, Tarp J, et al Physical activity and mortality: what is the dose response and how big is the effect?British Journal of Sports Medicine 2020;54:1125-1126.