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Meta-analysis: The Effect of Dietary Counseling for Weight Loss

Michael L. Dansinger, MD, MS; Athina Tatsioni, MD; John B. Wong, MD; Mei Chung, MPH; and Ethan M. Balk, MD, MPH
[+] Article and Author Information

From Tufts-New England Medical Center, Boston, Massachusetts.


Disclaimer: The authors of this report are responsible for its content. Statements in the report should not be construed as endorsement by the Agency for Healthcare Research and Quality or the U.S. Department of Health and Human Services.

Acknowledgment: The authors thank Ingram Olkin, PhD, Stanford University, for his invaluable assistance with our analyses.

Grant Support: This article is based on research conducted by the Tufts-New England Medical Center Evidence-based Practice Center funded under contract no. 290-02-0022 from the Agency for Healthcare Research and Quality of the U.S. Department of Health and Human Services. Dr. Dansinger is supported by National Institutes of Health grant K23RR020709.

Corresponding Author: Michael L. Dansinger, MD, Tufts-New England Medical Center, 750 Washington Street, NEMC #216, Boston, MA 02111; e-mail, mdansinger@tufts-nemc.org.

Potential Financial Conflicts of Interest: None disclosed.


Ann Intern Med. 2007;147(1):41-50. doi:10.7326/0003-4819-147-1-200707030-00007
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Background: Dietary and lifestyle modification efforts are the primary treatments for people who are obese or overweight. The effect of dietary counseling on long-term weight change is unclear.

Purpose: To perform a meta-analysis of the effect of dietary counseling compared with usual care on body mass index (BMI) over time in adults.

Data Sources: Early studies (1980 through 1997) from a previously published systematic review; MEDLINE and the Cochrane Central Register of Controlled Trials from 1997 through July 2006.

Study Selection: English-language randomized, controlled trials (≥16 weeks in duration) in overweight adults that reported the effect of dietary counseling on weight. The authors included only weight loss studies with a dietary component.

Data Extraction: Single reviewers performed full data extraction; at least 1 additional reviewer reviewed the data.

Data Synthesis: Random-effects model meta-analyses of 46 trials of dietary counseling revealed a maximum net treatment effect of −1.9 (95% CI, −2.3 to −1.5) BMI units (approximately −6%) at 12 months. Meta-analysis of changes in weight over time (slopes) and meta-regression suggest a change of approximately −0.1 BMI unit per month from 3 to 12 months of active programs and a regain of approximately 0.02 to 0.03 BMI unit per month during subsequent maintenance phases. Different analyses suggested that calorie recommendations, frequency of support meetings, inclusion of exercise, and diabetes may be independent predictors of weight change.

Limitations: The interventions, study samples, and weight changes were heterogeneous. Studies were generally of moderate to poor methodological quality. They had high rates of missing data and failed to explain these losses. The meta-analytic techniques could not fully account for these limitations.

Conclusions: Compared with usual care, dietary counseling interventions produce modest weight losses that diminish over time. In future studies, minimizing loss to follow-up and determining which factors result in more effective weight loss should be emphasized.

Figures

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Figure 1.
Study flow diagram.

Cochrane = Cochrane Central Register of Controlled Trials; NHLBI/NIDDK = National Heart, Lung, and Blood Institute/National Institute of Diabetes and Digestive and Kidney Diseases. *Not randomized or quasi-randomized; no usual care control; weight loss not goal of intervention; exercise-only intervention; intervention duration less than 12 weeks or follow-up duration less than 16 weeks; baseline body mass index less than 25 kg/m2; no weight change data; insufficient data to calculate standard error; duplicate publication of study; abstract or letter.

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Figure 2.
Study data and meta-analyses.

Net change in body mass index (BMI) by duration of dietary counseling–based weight loss interventions is shown. The size of each circle represents the weight of each study group in an overall random-effects model meta-regression. Boxes and vertical bars represent the summary estimates and 95% CIs, by random-effects model meta-analysis, of the net change in BMI at each time point; solid boxes are meta-analyses of active phases, and open boxes are maintenance phases. Where there were data from only 1 study group at a given time point, the 95% CI is of the single net change in that study group.

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Figure 3.
Slopes of individual studies during the active phase (top) and maintenance phase (bottom) of weight loss intervention.

Each line represents an individual intervention. Only studies that reported the net change in body mass index (BMI) at multiple time points are included. The letters represent individual studies; numbers after a letter indicate multiple intervention groups.

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Figure 4.
Meta-analyses of changes in body mass index (BMI) over time.

Summary slopes of net change in BMI for individual periods from 3 to 54 months. Slopes for periods starting at different times are arbitrarily placed on separate horizontal axes. The numbers of study groups included in each meta-analysis are shown at the end of each period. The pair of dotted lines from 3 to 12 months display the statistically significant subanalysis on the basis of intervention type. Because the absolute net changes were not included in the meta-analyses, only relative net change in BMI (slopes) is shown. *P = 0.009 (t test) for the difference between slopes in the active phase.

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Comments

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Why reporting change in BMI?
Posted on July 25, 2007
Salomon Banarer
Dallas Diabetes and Endocrine Center of Dallas
Conflict of Interest: None Declared

In their meta-analysis Dansinger et al report on the change in BMI achieved by dietary counseling. I am still trying to find a reasonable explanation as to why the authors chose this endpoint rather than absolute weight loss or percentage of excess weight loss. I adults, the height is expected to be constant. In fact, in many studies the height is only measured at the initial visit so by definition will be constant. If studies measure the height at every visit this will only introduce an error based on itraindividual variability. I do not question the value of BMI measurement for classification of nutritional status and for risk assessment but why report BMI changes when the title of the meta-analysis is effect in WEIGHT loss? As a clinician I understood that the article was going to tell my if dietary counseling works? and if so how much WEIGHT loss should I expect? The article did not provide a clear answer.

Conflict of Interest:

None declared

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