Weight Management

Citation:

Brinkworth GD, Noakes M, Parker B, Foster P, Clifton PM. Long-term effects of advice to consume a high-protein, low-fat diet, rather than a conventional weight-loss diet, in obese adults with Type 2 diabetes: one-year follow-up of a randomized trial. Diabetologia 2004; 47:1677-1686.

PubMed ID: 15480538
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To compare the long-term weight-loss and health outcomes at 1-year follow-up, after a 12-week intensive intervention consisting of two low-fat, weight-loss diets, which differed in protein content.
Inclusion Criteria:
  • adult
  • overweight (BMI: 27-40 kg/m2)
  • Type II diabetes
Exclusion Criteria:
  • proteinuria
  • liver disease
  • unstable cardiovascular disease
  • respiratory disease
  • gastrointestinal disease
  • a malignancy
Description of Study Protocol:

Recruitment

Subjects were recruited via public advertisement

Design

During the screening period, subjects were randomly assigned to either a low-protein or high-protein diet. Subjects were matched for sex, BMI and fasting glucose. The 64-week study consisted of three phases.

  • 8-week energy restriction period (~ 30% calorie restriction)
  • 4-week period in energy balance
  • Subjects were asked to maintain a similar dietary pattern for 52-weeks. During this time, there was minimal contact between the subjects and the dietary counselors.  Subjects were encouraged to return for follow-up visits every 3 months where body weight assessments were completed.

Blinding used (if applicable):  Not applicable

Intervention (if applicable)

Dietary intervention included either a low-protein diet (15% protein, 55% carbohydrate) or high-protein (30% protein, 40% carbohydrate). 

Statistical Analysis

  • Baseline differences were compared using unpaired t-tests
  • Analysis of variance with repeated measures was used to determine the effects of treatment, time of measurement, and their interactions on the dependent measures
  • 95% confidence intervals for the between group differences
  • Statistical significance is set at p value < 0.05
  • Data is presented as + SEM

 

Data Collection Summary:

Timing of Measurements

  • Body composition was completed at weeks 0, 12 and 64
  • On two consecutive days at weeks 0 and 12: body mass, height, resting blood pressure, blood lipids, glucose, insulin, HbA1c  and C-reactive protein concentrations.
  • Body weight at: 25, 38 and 51-weeks 

Dependent Variables

  • body weight and composition
  • blood pressure
  • glycemic control
  • c-reactive protein
  • albumin
  • blood lipids

Independent Variables

  • low-protein diet
  • high-protein diet

Control Variables

  • timing of measurements

 

Description of Actual Data Sample:

Initial N: 66 subjects

Attrition (final N): 38 subjects (15 men, 23 women)

Age: Low-protein (LP): 62.7 + 1.8 years, High-protein (HP): 60.9 + 1.8

Ethnicity: data not available

Other relevant demographics:

Anthropometrics:

  • weight (kg): 91.2 + 4.3 (LP), 96.2 + 4.0 (HP)
  • BMI (kg/m2): 33.3 + 1.3 (LP), 33.6 + 1.2 (HP)

Location: Australia

 

 

Summary of Results:

 

Variables (At 64 weeks)

Low-Protein Group

High-Protein Group

Statistical Significance of Group Difference

Body weight (kg)

-2.2 + 1.1

-3.7 + 1.0

p<0.01

Blood pressure (mm Hg)

10.0 + 3.2

1.9 + 1.9

p=0.04

Fasting glucose (mmol/l)

8.6 + 0.7

8.6 + 0.7

p= 0.26

CRP (mg/l)

3.6 + 0.7

3.8 + 0.8

p= 0.61

urinary albumin: creatinine (mg/mmol)

0.6 + 0.1

0.5 + 0.1

p= 0.91

Other Findings

  • Fasting glucose, insulin, HOMA and HbA1C concentrations were significantly reduced with energy restriction by week 12, but increased during the follow-up period such that there was no difference from baseline levels at week 64.
  • Serum trigylcerol, total cholesterol and the total cholesterol: HDL-C ratio had no difference at week 64 compared to baseline.
  • At week 64, urinary urea: creatinine ratio was significantly higher than baseline in the high-protein group (p=0.01), with no difference to baseline in the low-protein group (p=0.78).

 

Author Conclusion:
A high-protein weight-reduction diet may in the long term have a more favorable cardiovascular risk profile than a low-protein diet with similiar weight reduction in people with Type 2 diabetes.
Funding Source:
Industry:
Meadow Lea Foods (australia)
Food Company:
Reviewer Comments:

Large drop-out rate (lost to follow-up) likely due to lack of intervention from professionals during follow-up process and poor dietary compliance.  Authors note limitation of lack of dietary data, but creatinine excretion was used as a biomarker of protein intake. 

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? No
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? No
  6.6. Were extra or unplanned treatments described? No
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes