Weight reducing diets, mostly low in fat, may reduce the risk of early death in adults with obesity. However, the researchers were unable to show if there was any effect of weight reducing diets on heart disease and cancer.
The research provides further evidence of the clinical benefits associated with weight reducing diets, which have already been shown to prevent type 2 diabetes.
Adults with obesity have an increased risk of early death, heart disease, some cancers, type 2 diabetes and many other diseases.
The team of researchers based at the University of Aberdeen in Scotland and the University of Auckland in New Zealand reviewed data from randomised controlled trials (RCTs) to assess the effects of weight loss programmes on deaths from all causes as well as from heart disease and cancer.
Their study involved 54 trials with over 30,000 adults dating from 1966 to 2016 with a minimum follow-up time of one year.
Although not always adequately described, all but one of the trials included weight loss diets with sufficient information to establish that a reduction in fat intake was prescribed. Study design and quality of evidence were taken into account in the interpretation of findings.
The researchers identified high-quality evidence from 34 trials that showed that weight reducing diets decrease all-cause early death for adults with obesity - an 18% relative reduction in early death, corresponding to six fewer deaths per 1000 participants.
However, there was much less evidence for the effect of weight reducing diets on deaths from heart problems and cancer. The authors point out that there were fewer trials that reported events for these outcomes, providing lower quality evidence.
They also point out that they were unable to demonstrate differences between adults who had followed either a weight reducing diet alone, a weight reducing diet with exercise advice, or a weight reducing diet which provided an exercise programme to attend.
"We did not have sufficient data to examine whether other types of diet or physical activity influence outcomes or whether certain groups in the population are more or less likely to benefit" say the authors.
Nevertheless, they say "weight reducing diets, usually low in fat and low saturated fat, with or without an exercise component, may reduce premature all-cause mortality in adults who are obese."
"By implication our data support public health measures to prevent weight gain and facilitate weight loss using these types of diet" they conclude.