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DFA: Linoleic Acid (LA) and Intermediate Health Outcomes (2011)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • To analyze the fatty acid (FA) composition of serum phospholipids (S-PL) in healthy subjects and in groups of patients with type 2 diabetes mellitus (DM2) with varying duration of disease, degree of glucose intolerance, blood glucose control and type of treatment
  • To investigate the relationships between FA composition and insulin action to determine the relationship between altered FA pattern and insulin resistance in patients with DM2.
Inclusion Criteria:
  • All subjects were non-obese and those with DM2 were diagnosed as per the criteria of the American Diabetes Association
  • Healthy subjects were not taking any drugs and none had a family history of diabetes
  • All were euthyroid.
Exclusion Criteria:

No history or clinical evidience of a significant cardiovascular disease, respiratory, renal, hepatic, gastrointestinal or other diseases, alcoholism or drug abuse.

Description of Study Protocol:

Recruitment

Not described by author.

Design

Subjects were examined on an outpatient basis after an overnight fast. Subjects were instructed to follow their usual diet and lifestyle including to make no changes in food intake, alcohol intake or exercise.

  • A two-step hyperinsulinemic isoglycemic clamp study, taking five hours to complete, was conducted. A stepwise primed-continuous insulin infusion (one ml and 10ml per kg per minute of Actrapid HM) was given to acutely raise and maintain plasma concentrations of insulin.
  • Plasma glucose concentrations during the clamp were maintained at the fasting levels by continuous infusion of 15% glucose
  • Blood samples of plasma immunoreactive insulin (IRI) determination were taken before (zero minutes) and at 150, 175, 180, 270, 285 and 300 minutes of the clamp study
  • The OGTT was performed and blood for measuring plasma glucose, IRI and C-peptide was measured at 30, 60 and 120 minutes after the glucose load. 

Statistical Analysis

  • Data were analyzed using Kruskal-Wallis one-way analysis of variance (ANOVA)
  • Spearman rank correlation was used for testing the relationships between variables
  • The courses of plasma immunoreactive insulin (IRI) and C-peptide during the OGTT were evaluated using ANOVA with repeated measures and grouping factor
  • All data are expressed as mean ±SD.
Data Collection Summary:

Timing of Measurements 

  • A two-step hyperinsulinemic isoglycemic clamp study, taking five hours to complete, was conducted. A stepwise primed--continuous insulin infusion (one ml and 10ml per kg per minute of Actrapid HM) was given to acutely raise and maintain plasma concentrations of insulin.
  • Plasma glucose concentrations during the clamp were maintained at the fasting levels by continuous infusion of 15% glucose
  • Blood samples of plasma immunoreactive insulin (IRI) determination were taken before (zero minutes) and at 150, 175, 180, 270, 285 and 300 minutes of the clamp study
  • The OGTT was performed and blood for measuring plasma glucose, IRI and C-peptide were measured at 30, 60 and 120 minutes after the glucose load.

Dependent Variables

FA composition of S-PL mol percentage

  • 14:0
  • 16:0
  • 17:0
  • 18:0
  • 24:0.

Saturated FA

  • 16:1
  • 18:1
  • 24:1.

Monounsaturated FA

  • 18:2 n-6
  • 18:3 n-6
  • 20:3 n-6
  • 20:4 n-6
  • 20:5 n-6
  • n-6PUFA
  • n-6 DPUFA
  • 18:3 n-3
  • 20:5 n-3
  • 22:5 n-3
  • 22:6 n-3
  • n-3 PUFA.

Elongase

  • Δ6 desaturase
  • Δ5 desatruase
  • Δ9  desaturase.

Independent Variables

Insulin sensitivity

  • IRI  (µU per ml)
  • C-peptide (pmol per ml).
Description of Actual Data Sample:

Initial N

  • 53 males with DM2
  • 24 healthy subjects.

Attrition (Final N)

N/A.

Age

  • Healthy subjects: 39.8±3.1 years
  • DMN: 41±2.6 years
  • DMD: 46.1±3.6 years
  • DMH: 51.8±6.1 years.

Ethnicity

Not described.

Other Relevant Demographics

Groups were comparable in terms of BMI.

Anthropometrics

  • DMN Group (N=21): Were diagnosed within one year since screening, less than 45 years of age, treated with diet, with a BMI of less than 30kg/m2
  • DMD (N=11): With disease duration of more than eight years and treated with a diet
  • DMH (N=21): With disease duration of more than eight years and treated with glibenclamide
  • HS (N=24): Healthy subjects (males).

Location

Diabetes Center of the Institute for Clinical and Experimenatl Medicine, Prague, Czech Republic.

Summary of Results:

Key Findings

  • There was a significant decrease in the proportion of linoleic acid (18:2 m-6) in DMN (P<0.05), compared with heallthy subjects
  • A tendency to decrease was seen in DMH, but was not significant
  • Contents of n-6 DPUFA, in particular the propotion of arachidonic acid (20:4. n-6) are higher in all groups of diabetes, compared with HS (P<0.001)
  • Total contents of n-6 PUFA were unaltered in DMN and DMD
  • In DMH, the proportion of n-6 PUFA was higher compared to HS (P<0.01) and DMD (P<0.05) who are of the same age and with the same duration of diabetes
  • Groups are comparable in proportions of n-3 PUFA
  • Contents of SFA are similar in DMN, DMD and in HS, while in DMH the proportions of saturated FA are lower compared with HS (P<0.001) and DMD (P<0.001). The proportions of monounsaturated FA are unchanged in DMD and in DMH, whereas they are higher in DMN than in HS (P<0.01) and DMH (P<0.05).
  • Long-term blood glucose control (HbA1c) was worse in DMN and DMH, compared with DMD
  • In diabetics, the metabolic clearance rates of glucose at both insulin levels (MCRglusubmax and MCRglumax) were significantly reduced compared with HS (MCRglusubmax DMN, 5.35±2.7ml·kg-1 • min-1, DMH, 5.38±2.17ml • kg-1 • min-1; DMD 5.48±2.35ml • kg-1 • min-1 v HS, 10.9±3.3ml • kg-1 • min-1; P<0.01; MCRglumax DMN, 13.3±3.3ml • kg-1 • min-1; DMH, 12.5±3.0ml • kg-1 • min-1; DMD, 13.3±3.0ml • kg-1 • min-1; v HS, 17.4±3.8ml • kg-1 • min-1; P<0.05.
  • Increased contents of highly unsaturated n-6 family FA (P<0.01) arachidonic acid, in particular (DMN, 10.98±1.79%; DMD, 10.78±1.64%; DMH, 10.97±1.7% vs. HS, 8.51±1.53%; P<0.001), were found in all groups of diabetics compared with HS, while lower levels of linoleic acid were seen in DMN (P<0.001) and DMH (P<0.05)
  • The contents of saturated FA and monounsaturated FA were comparable in HS, DMN and DMD. While in HS, there were significant negative correlations between MCRglu and the contents of saturated FA and a positive association between insulin action and proportions of linoleic and arachidonic acids, no significant relationships were found in diabetic subject.
  • Different groups of DM2 patients show an altered FA pattern of S-PL, which is not related to insulin action.
Author Conclusion:
  • An altered FA composition of S-PL in groups of DM2 patients with different mean ages, duration of disease, degrees of glucose intolerance, blood glucose control and type of treatment
  • The shifts in the proportions of n-6 FA were a general finding in diabetic subjects, while no differences were seen in the contents of saturated FA, monunsaturated FA and n-3 family FA
  • A lower content of linoleic acid and higher proportions DPUFA n-6 were found in diabetics, compared with HS
  • Decreased insulin action at both insulin levels in type 2 diabetic subjects were found
  • The degrees of IR were comparable in all groups of diabetics; IR was independent of the duration of disease, long-term blood glucose control or type of treatment
  • No significant association between insulin action and the FA composition of S-PL was found
  • The absence of relationships supports the hypothesis that the alterations in the FA composition of lipids are not the direct cause of of IR in diabetes.
Funding Source:
Government: Health Ministry of the Czech Republic (Project No. NB/490-3)
Reviewer Comments:
  • Dietary intake data was a rough estimate and did not show differences between groups. However, the methods used for estimating the diet composition over- or underestimate the intake of dietary fat. Altered dietary intake may be responsible for the differences in the FA pattern seen between groups.
  • Physical fitness was not estimated in the study, which may impact FA composition of lipids
  • Treatment with glibenclamide may be a cause of the different FA paterns in DMH, compared with the other diet-treated diabetic groups.
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? 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? Yes
  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.) Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? ???
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  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%.) N/A
  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? Yes
5. Was blinding used to prevent introduction of bias? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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? ???
  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? ???
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? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  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? N/A
  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? Yes
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? 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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  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? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes