Weight-loss diets, such as those low in fat and saturated fat consumption, with or without added exercise, may reduce the risk for all-cause mortality in obese adults, according to a study published in the BMJ.
The research team, led by Chennan Ma, from the Health Services Research Unit at the University of Aberdeen in Scotland, conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) using random effects, estimating risk ratios, and mean differences to assess whether weight loss interventions for adults with obesity affect all-cause, cardiovascular, and cancer mortality, as well as cardiovascular disease, new cancer development, and body weight change. The researchers searched multiple databases for all long-term (≥1 year) RCTs of weight loss interventions for adults with obesity recorded from January 1966 to December 2015.
Subgroup analyses were recorded for sex, age (<60 years vs ≥60 years), BMI (<35 vs ≥35), glycemic control (normal vs impaired glucose tolerance or impaired fasting glucose vs type 2 diabetes), ethnicity, and physical activity interventions (none vs advice only vs exercise program provided).
A total of 1,174 full text trial reports were screened with 5,982 titles and abstracts and 54 RCTs for inclusion in the final review. These studies provided 30,206 adults with obesity; all but one trial evaluated low-fat, weight-reducing diets. High quality evidence showed that weight loss interventions decrease all-cause mortality (34 trials, 685 events; risk ratio [RR], 0.82), with 6 fewer deaths per 1000 participants. For other primary outcomes, moderate quality evidence showed an effect on cardiovascular mortality (8 trials, 134 events; RR, 0.93), and very low quality evidence showed an effect on cancer mortality (8 trials, 34 events; RR, 0.58).
For secondary outcomes, 24 trials (15,176 participants) reported high quality evidence on new cardiovascular events (1,043 events; RR, 0.93), and 19 trials (6,330 participants) provided very low quality evidence on participants developing new cancers (103 events; RR, 0.92).
“We found high quality evidence that weight reducing diets for adults with obesity, usually low in fat and low in saturated fat, were associated with an 18% relative reduction in premature mortality over a median trial duration of 2 years, corresponding to 6 fewer deaths per 1000 participants (95% confidence interval 2 to 10),” the researchers stated. “This evidence provides a further reason for weight reducing diets to be offered alongside their already proven benefits, such as type 2 diabetes prevention.”
Ma C, Avenell A, Bolland M, et al. 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