Obesity Clinical Trial
Official title:
Effect of Liquid Versus Solid Calories on Body Weight: a Systematic Review and Meta-analysis of Controlled Feeding Trials
Consumption of sugar-sweetened beverages (SSBs) has been linked to rising rates of overweight and obesity. The most prominent mechanism to explain the link between SSBs and obesity is that liquid calories are not perceived by the body; thereby, promoting less satiety, less energy compensation and more weight gain than does the same energy consumed in solid form. This view is supported by pooled analyses of acute preload trials that have primarily measured food intake as the outcome. Though failure of short-term compensation has been observed with liquid calories, results from these acute preload trials should not be extrapolated to infer that liquid energy sources lead to weight gain over the long-term. To date, it is unclear whether liquid calories have differential effects than solid calories on body weight gain over the longer term. To increase clarity in this issue, the investigators propose to conduct a systematic review and meta-analysis from long-term controlled feeding trials to distinguish the contribution of liquid calories from solid calories on body weight over the long-term. The findings generated by this analysis will improve the health of consumers through informing evidence-based guidelines and improving health outcomes by educating healthcare providers and patients, stimulating industry innovation, and guiding future research design.
Background: The prevalence of overweight and obese individuals has dramatically risen over
the past 30 years and represents a major threat to public health. Sugars consumed in liquid
form (i.e. SSBs) have been targeted as a prominent contributor towards obesity. Pooled
analyses of acute preload trials that have assessed food intake as the primary outcome
suggest that liquid calories from sugars are more poorly compensated than solid calories.
Though tempting, results from these acute studies should not be extrapolated to infer that
liquid energy sources lead to weight gain over the long term. A study of long-term
randomized controlled trials by Kaiser et al. found that when adults were required to
consume sugar sweetened beverages (SSBs) as an additional source of energy, dose-dependent
weight gain was observed. However, this weight gain was far less than half the amount one
would have predicted to be gained using a mathematical model. This suggests that over
extended periods of time, majority of the energy consumed as SSBs is indeed compensated for.
Need for proposed research: To date, it is unknown whether people compensate differently for
liquid versus solid sources of calories over the long term.
Objective: To synthesize evidence of the effect of liquid calories versus solid calories on
body weight in controlled trials.
Design: This systematic review and meta-analysis will be conducted according to the Cochrane
Handbook for Systematic Reviews of Interventions and reported according to the Preferred
Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).
Data sources: MEDLINE, EMBASE, and The Cochrane Central Register of Controlled Trials
(Clinical Trials; CENTRAL) will be searched using appropriate search terms supplemented by
hand searches of references of included studies.
Study selection: The investigators will include controlled trials (randomized and
non-randomized) that have compared the effects of liquid sources of calories in isocaloric
exchange for solid sources of calories on body weight for >= 7 days in humans (healthy or
non-healthy).
Data extraction: Following systematic exclusion based on title and abstract, 2 reviewers
will independently review and extract relevant data from each report that meets the
inclusion criteria. Risk of bias will be assessed using the Cochrane Risk of Bias Tool. All
disagreements among reviewers were resolved by consensus. Missing variance data will be
calculated using standard computations and imputations.
Outcomes: Body weight (kg)
Data synthesis: Pooled analyses of the mean difference will be performed using the generic
inverse variance method. Random-effects models will be used even in the absence of
statistically significant between-study heterogeneity because they yield more conservative
summary effect estimates in the presence of residual heterogeneity. Fixed-effects models
will be used only if there are less than 5 included trials. Crossover trials will be
assessed via paired analyses. Heterogeneity will be assessed by the Cochran Q statistic and
quantified by the I2 statistic. Sensitivity and subgroup analyses will be conducted to
identify sources of heterogeneity. Sensitivity analyses will involve an assessment of
heterogeneity upon systematic removal of each trial. If there are >= 10 trials, the study
investigators will conduct apriori subgroup analyses by age, health status, comparator,
dose, baseline measurements, randomization, study design (parallel, crossover), energy
balance (positive, neutral, negative), follow-up (<= 4 weeks, > 4 weeks) and risk of bias.
Meta-regression analyses will assess the significance of categorical and continuous subgroup
analyses. When more than 10 trials are available, publication bias will be investigated by
funnel plots and formal testing using Egger and Begg tests. If publication bias is
suspected, then the investigators will attempt to adjust for funnel plot asymmetry by
imputing the missing study data using the Duval and Tweedie trim and fill method.
Evidence assessment: The strength of the evidence for each outcome will be assessed using
the Grading of Recommendations Assessment, Development and Evaluation (GRADE).
Knowledge translation plan: The results will be disseminated through interactive
presentations at local, national, and international scientific meetings and publication in
high impact factor journals. Target audiences will include the public health and scientific
communities with interest in nutrition and obesity. Feedback will be incorporated and used
to improve the public health message and key areas for future research will be defined.
Applicant/Co-applicant Decision Makers will network among opinion leaders to increase
awareness and participate directly as committee members in the development of future
guidelines.
Significance: The proposed research will aid in distinguishing the role of liquid calories
from solid calories on body weight over the long-term. This will strengthen the
evidence-base for guidelines and improve health outcomes by educating healthcare providers
and patients, stimulating industry innovation, and guiding future research design.
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Time Perspective: Prospective
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