DM: Protein (2007)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:

The purpose of this study was to determine the effect of co ingestion of varied amounts of fat and protein in a mixed meal on carbohydrate metabolism in subjects with type 2 diabetes mellitus.

Inclusion Criteria:

Type 2 diabetes mellitus

Exclusion Criteria:

Digestion or absorption disorders.

Description of Study Protocol:

Recruitment:  Subjects were hospitalized patients with type 2 diabetes.

Design:  Subjects were received 3 different test breakfasts by random assignment on 3 consecutive days after fasting overnight and before taking medications.

Blinding Used (if applicable):  not specified

Intervention (if applicable):

 Test meals:

Group 1: Isocaloric (400), 60% carbohydrate;

  • normal: 10% fat and 15% protein
  • fat rich: 15% fat, 0 protein
  • Protein rich: 0 fat, 40% protein.

Group 2: 

  • reduced fat: 310 kcal, 50% carbohydrate, 1% fat, 25% protein
  • normal fat: 400 kcal, 50% carbohydrate, 10% fat, 25% protein
  • high fat: 500 kcal, 50% carbohydrate, 20% fat, 25% protein.

Statistical Analysis:

  • results given as mean ± SEM
  • Wilcoxon's test and analysis of variance with Scheffe's procedure used for statistical comparisons
  • P<0.05 considered significant

 

Data Collection Summary:

Timing of Measurements:  Blood sampling at baseline and after breakfast

  • group 1: 30, 60, 120 and 180 minutes
  • group 2: 30, 60, 90, 120, 180 and 300 minutes.

Dependent Variables:

  • Glucose
  • insulin
  • c-peptide
  • gastric inhibitory polypeptide, measured radioimmunologically by using GIP antibody from rabbits
  • triglyceride and glucagon response to meals

Independent Variables

  • Group 1: Isocaloric (400), 60% carbohydrate;
    • normal: 10% fat and 15% protein
    • fat rich: 15% fat, 0 protein
    • Protein rich: 0 fat, 40% protein.

    Group 2: 

    • reduced fat: 310 kcal, 50% carbohydrate, 1% fat, 25% protein
    • normal fat: 400 kcal, 50% carbohydrate, 10% fat, 25% protein
    • high fat: 500 kcal, 50% carbohydrate, 20% fat, 25% protein.

Control Variables:  not specified

 

Description of Actual Data Sample:

Initial N:  24 hospitalized patients were divided into 2 matched groups.

Final N: 24

Age

  • Group 1: 65.6±2.6 SEM yr; range 50-78
  • Group 2: 66.7±3.1 yr; range 38-74

Ethnicity:  not specified

Other relevant demographics:

14 patients treated with glibenclamide and 10 with diet only

Anthropometrics:

  • Group 1: BMI: 26.6±1.2
  • Group 2: BMI: 25.8±1.2

Location:  The study was conducted on hospitalized patients in Heidelberg, Germany

Summary of Results:

 

Group 1: mean glucose concentrations were not significantly different among the different test meals.

There were significant differences for insulin after 120 minutes:

  high  protein high fat normal Significance
Insulin pmol/L 478+164 160+ 56 246+ 74 (P<0.05)

Glucagon was significantly higher at 30 minutes on the protein rich meal.

Triglycerides were significantly higher  180 minutes after the high fat meal.

Group 2: Mean concentrations of glucose, C peptide, insulin, and glucagon showed no significant differences among the test meals.

Triglycerides were significantly higher after the high fat meal at 180 minutes (P<0.05). GIP was significantly higher 120 minutes after the high fat meal.

GIP was not significantly different among the test meals.
Author Conclusion:

Neither varying the ratio of fat to protein in group 1 nor increasing the amount of fat in group 2 affected glucose concentrations after the test meals.

Compared with the changes after a standard breakfast, insulin increased after a protein rich meal and decreased after a fat rich meal in group 1, while glucose and GIP remained constant.

In contrast, only GIP showed a significant increase after a high-fat meal in group 2.

In people with type 2 diabetes, glucose and insulin responses to different mixed diets do not appear to be exclusively mediated by GIP.

Protein was confirmed as a potent stimulator of insulin secretion.

Funding Source:
University/Hospital: University of Tubingen
Reviewer Comments:
This study demonstrate that increasing protein at meals from 0 to 40 g increased  insulin but not glucose.
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? No
3. Were study groups comparable? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  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")? N/A
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? N/A
  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? Yes
  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? Yes
  6.6. Were extra or unplanned treatments described? N/A
  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? ???
  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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? ???
  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? No
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