CRD summary

This review found that sugar intake affected body weight, apparently due to changes in overall energy intake. Despite some concerns over potential for bias in the studies and possible publication bias, the author’s conclusions are likely to be reliable.

Authors' objectives

To investigate the association between dietary intake of sugars and body weight, in adults and children.

Searching

PubMed, EMBASE, Scopus, Web of Science and CINAHL were searched, for articles written in English, up to December 2011. Search terms were reported. The references of existing meta-analyses and reviews were searched.

Study selection

Randomised controlled trials (RCTs) and cohort studies were eligible for inclusion, if they reported the intake of sugars or sugar containing foods or beverages, and measured body size, including weight change, body mass index change, waist circumference, and body or trunk fat percentage. Participants were adults or children without acute illness; participants with diabetes were eligible. RCTs had to be of at least two weeks’ duration. Trials of interventions designed to achieve weight loss were excluded. Cohort studies were eligible, but only the results from the RCTs are considered here.

In some of the RCTs, participants were advised to reduce their sugar intake, in others they had to increase their sugar intake, without strict attempts to control weight. Differences in sugar intake between trial arms ranged from 1% to 14% of participants' total energy intake. Some trials sought to achieve isoenergetic replacement of sugars with other carbohydrates.

Two reviewers independently selected the studies, with disagreements resolved by discussion.

Assessment of study quality

RCT quality was assessed using the Cochrane risk of bias tool, covering sequence generation, allocation concealment, blinding, outcome assessment, completeness of data, and outcome reporting. The overall quality of the evidence was assessed using GRADE criteria.

Two reviewers independently assessed quality, with disagreements resolved by discussion.

Data extraction

From the RCTs, the mean differences or standardised mean differences in body size (however assessed), between trial arms, were extracted, with their corresponding 95% confidence intervals.

Methods of synthesis

The effect estimates were pooled across trials, in random-effects meta-analyses. Heterogeneity was assessed using Ι² and Cochran’s Q. An Ι² of over 50% was taken to indicate heterogeneity.

Sensitivity analyses were used to investigate the effects of study duration and of removing studies that had a difference in sugar intake of less than 5% of the total energy intake. Meta-regression was used to investigate a possible dose-response relationship, and the effect of study duration and design.

Publication bias was assessed in forest plots and the Egger test, and the trim-and-fill method was used to adjust for possible bias.

Results of the review

There were 30 eligible RCTs, with 4,960 participants (range eight to 1,140). The quality of the RCTs varied, with most trials being unblinded; it was generally unclear whether the outcome assessors were blind to treatment allocation.

Trials of Adults: Five trials investigated the effect of reducing dietary sugar intake, with study duration ranging from 10 weeks to eight months. Reducing dietary sugar reduced weight (MD -0.80kg, 95% CI -0.39 to -1.21; Ι²=17%). Ten trials investigated the effect of increasing sugar intake, with study duration ranging from two weeks to six months. Increasing dietary sugar increased weight (MD 0.75kg, 95% CI 0.30 to 1.19; Ι²=82%). The weight gain was greater in the two trials that lasted over eight weeks (MD 2.73kg, 95% CI 1.68 to 3.78). Twelve trials investigated isoenergetic exchange of sugars, with study duration ranging from two weeks to six months. There was no evidence that differences in sugar intake affected weight when energy intake was equivalent.

Trials of children: In five trials of children, where advice on sugar reduction was given, there was no association between receiving this advice and body mass index.

There was no evidence of a dose-response relationship between sugar intake and weight, nor did study duration and design alter the results. There was evidence of publication bias. The trim-and-fill analysis suggested that correcting for the bias reduced the effect sizes, but all statistically significant results remained significant.

Authors' conclusions

Intake of sugar affected body weight in people who were not on controlled diets. This change in weight appeared to be due to energy intake, as isoenergetic exchange of sugars for other carbohydrates was not associated with weight change.

CRD commentary

This was generally a well-conducted review, with a clear research question and appropriate inclusion criteria. A suitable search was performed, but it was limited to studies in English and unpublished studies were not sought, so some relevant data may have been missed. Action was taken to reduce reviewer error and bias throughout the review. Study quality was assessed and was variable, with particular issues around the lack of blinding to treatment of patients and outcome assessors, which may have led to bias.

A large number of studies were identified, but most were very small, with considerable diversity in how sugar intake was varied. The trial data were synthesised in suitable meta-analyses. The authors identified possible publication bias, but analyses to compensate for the bias suggested that the conclusions were unlikely to be altered.

Despite some concerns over the potential for bias within studies and over publication bias, the authors' conclusions are likely to be reliable.

Implications of the review for practice and research

Practice: The authors suggested that advice on sugar intake was a relevant component of strategies to reduce obesity.

Research: The authors made no recommendations for research.

Funding

Supported by the University of Otago, New Zealand; the Riddet Institute, New Zealand; and the World Health Organization.

Bibliographic details

Te Morenga L, Mallard S, Mann J. Dietary sugars and body weight: systematic review and meta-analyses of randomised controlled trials and cohort studies. BMJ 2013; 346: e7492. [PubMed: 23321486]

Original Paper URL

http://www.bmj.com/content/346/bmj.e7492

Indexing Status

Subject indexing assigned by NLM

MeSH

Beverages /adverse effects; Cohort Studies; Dietary Sucrose /adverse effects; Energy Intake; Humans; Obesity /etiology; Overweight /etiology; Randomized Controlled Trials as Topic; Weight Gain; Weight Loss

AccessionNumber

12013003284

Database entry date

21/01/2013

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.