ArticlesEffect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: a systematic review and meta-analysis
Introduction
Identifying effective strategies for long-term weight control will be crucial to reduce the alarming prevalence of overweight and obesity worldwide. The macronutrient composition of the diet—the proportions of calories contributed by fat, carbohydrate, and protein—has received substantial attention in the past few decades for its potential relevance in weight loss and weight maintenance.1, 2 Many short-term and long-term randomised trials1, 3, 4, 5 across various general and clinical populations have attempted to identify the optimum ratio of macronutrients for weight loss. Lowering the proportion of daily calories consumed from total fat has been targeted for many reasons, one of which is that 1 g of fat contains more than twice the calories of 1 g of carbohydrates or protein (9 kcal/g vs 4 kcal/g). Thus, a reduction in total fat intake could theoretically lead to an appreciable effect on total calories consumed. However, results of randomised trials3, 6, 7, 8 have failed to consistently show that reducing the proportion of energy consumed from total fat leads to long-term weight loss compared with other dietary interventions.
This systematic review and meta-analysis aimed to summarise the large body of evidence from randomised control trials (RCTs) lasting at least 1 year in which weight changes in participants on low-fat diets versus other dietary interventions were compared. Trials were included irrespective of whether weight loss was intended or not, such as studies assessing lipids or cancer endpoints. We aimed to stratify the analysis by characteristics of the interventions that might affect differences in weight loss, including whether the intervention groups received similar attention and intervention intensity, or the composition of the comparison diet. We postulated that low-fat diets would not be associated with greater weight loss than other interventions when differences in these intervention characteristics were taken into account, and that differences in weight loss favouring higher-fat interventions would be larger when adherence was greater.
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Search strategy and inclusion criteria
We predefined our search strategy, study eligibility criteria, and statistical approaches for this systematic review and meta-analysis in an unpublished research protocol, according to PRISMA guidelines. We used MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and Cochrane Database of Systematic Reviews to identify eligible trials. The following terms were included in the MEDLINE search, with similar terms used in the other databases: (low fat diet[MeSH] OR “low fat”
Results
Our search yielded 3517 citations (figure 1), of which 53 RCTs were eligible for inclusion in our analysis (69 comparisons; table 1). Most of the trials were undertaken in North America (n=37) and were 1 year in duration (n=27). 20 trials specifically enrolled participants with prevalent chronic diseases, including breast cancer,23, 60, 61, 62 hypercholesterolaemia,16, 29, 30 type 2 diabetes,5, 17, 22, 31, 33, 34, 37, 39, 55 metabolic syndrome,41 oesophageal metaplasia,42 ischaemic heart
Discussion
Results from this comprehensive meta-analysis of RCTs with at least 1 year of follow-up suggest that low-fat dietary interventions do not lead to greater weight loss than do low-carbohydrate and other higher-fat dietary interventions of a similar intensity, irrespective of the weight loss intention of the trial. In fact, in the setting of weight loss trials, higher-fat, low-carbohydrate dietary interventions led to a slight but significant, greater long-term weight loss than did low-fat
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2023, American Journal of Clinical Nutrition