Systematic review and meta-analysis
Long term weight maintenance after advice to consume low carbohydrate, higher protein diets – A systematic review and meta analysis

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Abstract

Background

Meta analysis of short term trials indicates that a higher protein, lower carbohydrate weight loss diet enhances fat mass loss and limits lean mass loss compared with a normal protein weight loss diet. Whether this benefit persists long term is not clear.

Methods and results

We selected weight loss studies in adults with at least a 12 month follow up in which a higher percentage protein/lower carbohydrate diet was either planned or would be expected for either weight loss or weight maintenance. Studies were selected regardless of the success of the advice but difference in absolute and percentage protein intake at 12 months was used as a moderator in the analysis. Data was analysed using Comprehensive Meta analysis V2 using a random effects analysis. As many as 32 studies with 3492 individuals were analysed with data on fat and lean mass, glucose and insulin from 18 to 22 studies and lipids from 28 studies. A recommendation to consume a lower carbohydrate, higher protein diet in mostly short term intensive interventions with long term follow up was associated with better weight and fat loss but the effect size was small-standardised means of 0.14 and 0.22, p = 0.008 and p < 0.001 respectively (equivalent to 0.4 kg for both). A difference of 5% or greater in percentage protein between diets at 12mo was associated with a 3 fold greater effect size compared with <5% (p = 0.038) in fat mass (0.9 vs. 0.3 kg). Fasting triglyceride and insulin were also lower with high protein diets with effect sizes of 0.17 and 0.22, p = 0.003 and p = 0.042 respectively. Other lipids and glucose were not different.

Conclusion

The short term benefit of higher protein diets appears to persist to a small degree long term. Benefits are greater with better compliance to the diet.

Introduction

High protein weight loss diets are widely used but there is no consensus about the long term efficacy of these diets. Short to medium term studies have clearly shown that ad libitum high protein diets increase satiety and increase weight loss compared to high carbohydrate diets [1], [2] but long term 1–2 year compliance with high protein diets is usually poor despite intensive support [3] but this is no different from compliance to any other macronutrient prescription. A recent meta analysis [4] showed a small benefit from high protein diets but this study selected only studies in which the dietary intervention was successful at achieving the planned macronutrient intake with a reported difference in protein intakes of 5% or more between groups. Another review came to a similar conclusion finding that when protein intake was increased by less than 5% no benefit was seen in weight loss outcomes while successful studies with greater weight loss with high protein diets had an increase in protein intake of 24% over baseline intakes [5]. As compliance to the protein prescription is very likely to be related to compliance to the energy prescription these positive findings do not show that adoption of a high protein weight loss or weight maintenance diet per se will necessarily lead to a better weight outcomes long term. However the positive findings of the weight maintenance phase of the DIOGENE study (especially the shop centres where food was provided) suggest that providing more protein moderates food intake in some circumstances and a change of 5% is all that is required [6]. Similarly short term isocaloric energy controlled weight loss studies show that high protein diets improve body composition compared with isocaloric high carbohydrate weight loss diets [7]. However it is not clear if providing only advice to consume a low carbohydrate, high protein diet for weight loss or weight maintenance with or without intensive support provides any advantages long term over any other type of advice and a recent selective meta analysis of low fat interventions in adults has suggested essentially no benefit over 12 months with the high protein diet other than a reduced fasting insulin Ref. [8]. The purpose of this review and meta analysis is to examine this question in more detail in a broader group of studies with no macronutrient or study design limitations.

Section snippets

Search strategy

We followed standard criteria for conducting and reporting meta-analyses of observational studies [9]. We conducted systematic literature searches, from the index date of each database through July 2013, of multiple databases including PubMed (http://www.ncbi.nlm.nih.gov/pubmed, since 1966), EMBASE (http://www.embase.com, since 1947), the Cochrane Library.

(http://www.thecochranelibrary.com/, since 1951) to identify all randomised controlled trials where the two diets potentially contained a

Results

Searches identified (Embase 609, Cochrane 369, Pubmed 4103) potential articles of which all but 57 were excluded simply on the basis of title and abstract (Supplementary data Fig. 1). Most clinical weight loss trials identified were eliminated at the abstract stage because of their short duration. After eliminating multiple reports of the same study, a total of 34 separate articles (for 32 studies, one was a limited 6 year follow up and the other was a limited 3 year follow up) contained

Discussion

We have shown in this analysis that a recommendation to lower carbohydrate intake and to maintain or increase the amount of protein in a weight loss diet (or this increase in protein would be expected based on the reduction in carbohydrate) leads to a small long term effect on weight and fat mass compared to advice to reduce protein. This is unexpected given that many studies had active intervention periods of <6 months and the remainder of the time was weight maintenance strategies or passive

Funding

This review was funded by the National health and Medical Research Council of Australia through a Principal Research Fellowship to PMC.

Acknowledgements

PMC devised the study and analysed the data and drafted the manuscript while DC and JBK performed the data extraction and contributed to the manuscript. PMC is the Co author of several diet books that encourage a high protein diet while DC and JBK have no conflicts of interest.

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