DM: Protein (2007)

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

To measure the effect of protein ingestion on circulating glucose concentrations in persons with type 2 diabetes.

Inclusion Criteria:
Untreated type 2 diabetes
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:

Recruitment:  volunteers were studied in the Special Diagnostic and Treatment Unit of the Veterans Affairs Medical Center in Minneapolis, MN.

Design: subjects were randomly given beef protein or water after a 13-hour fast.  Arterialized blood samples were drawn periodically for 8 hours while the subjects fasted.

Blinding Used (if applicable):  not specified

Intervention (if applicable):

1. Subjects ingested their usual energy intake and >=200 g carbohydrate/d for 3 days before the study.

2. Subjects were admitted to a special unit the evening before the study and were given a standardized meal at 1700 hr.

3. At 0300 hr on the day of the study, catheters were placed for infusion of tritium labeled glucose and bicarbonate at a constant rate of –0.11 µCi glucose/min and –0.52 µCi 14C HC03/min respectively until 1600 hr.

4. At 0800 hr, subjects were randomly assigned water or 50 g beef protein and for the remainder of the day consumed only water.

Statistical Analysis

  • multivariate ANOVA
  • t tests when data were significantly different
Data Collection Summary:

Timing of Measurements

Arterial blood samples were drawn hourly from 0300 to 0700 hr and then every 15 minutes until 0800, then every 15 minutes for 90 minutes, then every 30 minutes for 150 minutes and every hr for the final 4-hr of the study.

Dependent Variables

  • Plasma glucose response
  • Serum immunoreactive insulin
  • Plasma glucagon response
  • Rate of gluconeogenesis (incorporation of 14C-HC03)
  • Amino acid response

Independent Variables:

  • Subjects were randomly given beef protein or water after a 13-hour fast

Control Variables:  factors included in ANOVA were not specified

Description of Actual Data Sample:

Initial N:  10 males

Final N:  10

Age:  Mean age, y: 65 ± 4.0 SEM

Ethnicity:  not specified

Other Relevant Demographics: mean duration of diabetes: 24 months, range 2-79 months

Anthropometrics:  Mean BMI: 30 ± 2.1 SEM

Location:  USA

Summary of Results:

Glucose:

In response to water ingestion, gradual decrease in serum glucose concentration over 8 hr

Response to 50 g beef protein, small initial and transient increase in glucose, but by 2.5 hr, glucose had decreased and continued to decrease over time.

Insulin:

In response to water, insulin decreased only slightly.

In response to 50 g beef protein, there was a prompt rise in mean insulin concentration (~3 fold) and did not return to fasting levels until 7 hr after the meal and was significantly higher than water and than fasting (P<0.01).

Glucagon:

In response to water, was unchanged.

In response to 50 g beef protein, significantly greater than water and than fasting (P<0.01).

Gluconeogenesis:

The gluconeogenic rate as estimated by the incorporation of 14C HC03 into glucose was nearly the same whether water or protein was ingested.

Amino Acid Response:

alpha-amino nitrogen response was unchanged after ingestion of water, but increased after ingestion of 50 g meat protein, which was significantly different than water and than fasting (P<0.01)

Author Conclusion:

Protein ingestion resulted in an increase in circulating insulin, C-peptide, glucagons, a- amino and urea nitrogen, and triglycerides; a decrease in nonesterified fatty acids; and a modest increase in respiratory quotient.

The total amount of protein deaminated and the amino groups incorporated into urea was calculated to be ~20-23 g. The net amount of glucose estimated to be produced based on the quantity of protein deaminated, was ~11-13 g. However, the amount of glucose appearing in the circulation was only ~2 g. The peripheral plasma glucose concentration decreased by 1 mmol after ingestion of either protein or water, confirming that ingested protein does not result in a net increase in glucose concentration, and results in only a modest increase in the rate of glucose disappearance.

Funding Source:
University/Hospital: University of Minnesota
Reviewer Comments:

This study demonstrates that ingestion of protein does not increase plasma glucose in individuals with type 2 diabetes mellitus. Therefore, the amount of protein in meals and snacks would not be expected to influence postprandial glucose or glycemic control.

Subjects were randomized into two groups, but the demographic, anthropometric, and health characteristics of the groups were not compared.

This study was partially sponsored by the Minnesota Beef Council.

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) N/A
 
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? ???
3. Were study groups comparable? ???
  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? ???
  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? N/A
  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? N/A
  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? N/A
  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? No
  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? N/A
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? No
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? No