Dr Lee Hooper and colleagues investigated the relation between total fat intake and body weight in adults and children.
The team performed a systematic review and meta-analysis of randomized controlled trials and cohort studies.
The team searched Medline, Embase, CINAHL, and the Cochrane Central Register of Controlled Trials to 2010.
The researchers identified randomized controlled trials and cohort studies of adults or children that compared lower versus usual total fat intake, and assessed the effects on measures of body fatness after at least six months or 1 year.
Randomized controlled trials with any intention to reduce weight in participants or confounded by additional medical or lifestyle interventions were excluded.
Data were extracted and validity was assessed independently, and in duplicate.
|There were reductions in body weight in studies with baseline fat intakes of 28-43% of energy intake|
|British Medical Journal|
The team included 33 randomized controlled trials, and 10 cohort studies, all from developed countries.
The doctors reported that meta-analysis of data from the trials suggested that diets lower in total fat were associated with lower relative body weight.
Lower weight gain in the low fat arm compared with the control arm was consistent across trials, but the size of the effect varied.
The team noted that greater reduction in total fat intake and lower baseline fat intake were associated with greater relative weight loss, explaining most of the heterogeneity.
The significant effect of a low fat diet on weight was not lost in sensitivity analyses.
The team of doctors found that the lower total fat intake also led to lower body mass index and waist circumference.
There was no suggestion of negative effects on other cardiovascular risk factors.
The research team noted that GRADE assessment suggested high quality evidence for the relation between total fat intake and body weight in adults.
Only 1 randomized controlled trial and three cohort studies were found in children and young people, but these confirmed a positive relation between total fat intake and weight gain.
Dr Hooper and colleagues conclude, "There is high quality, consistent evidence that reduction of total fat intake has been achieved in large numbers of both healthy and at risk trial participants over many years."
"Lower total fat intake leads to small but statistically significant and clinically meaningful, sustained reductions in body weight in adults in studies with baseline fat intakes of 28-43% of energy intake, and durations from 6 months to over 8 years."
"Evidence supports a similar effect in children and young people."