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

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To examine predictive factors for abdominal obesity or metabolic syndrome, and to investigate the association of plasma fatty acid composition, estimated desaturase activity and nutrient intakes, with abdominal obesity or metabolic syndrome in Japanese males.

Inclusion Criteria:

Patients were included based on the Diagnostic criteria of metabolic syndrome

  • Abdominal obesity (waist circumference ≥85cm) plus two or more of the following three criteria:
    • Dyslipidemia (≥150mg/dL and /or high density lipoprotein cholesterol <40mg/dL)
    • Elevated blood pressure (systolic blood pressure ≥130mmHg, or diastolic blood pressure ≥85mmHg)
    • Impaired glucose tolerance (fasting glucose ≥110mg/dL).

The control group had no abdominal obesity, dyslipidemia, diabetes or elevated blood pressure.

Exclusion Criteria:

Participants receiving treatment for diabetes, hypertension and dyslipidemia were excluded.

Description of Study Protocol:


187 males invited to participate, 119 provided informed consent. Finally, data from 94 participants were analyzed.


Non-randomized control trial; Clinical characteristics, the fatty acid composition of plasma cholesteryl esters, and energy and nutrient intakes were analyzed in three groups (Japanese males): Metabolic syndrome (MS, N=24), abdominal obesity (OB, n=43), and control (N=27). Food frequency questionnaires were used.The estimated desaturase activities were calculated by the ratio of 16:1n-7/16:0, 18:3n-6/18:2n-6, and 20:4n-6/20:3n-6 in plasma cholesteryl esters as surrogates of the measure of the delta 9, delta 6, delta 5 desaturase (D9-16D, D6D and D5D) activities, respectively. Metabolic syndrome risk factors were assessed and investigated the association of plasma fatty acid composition, estimated desaturase activity, and nutrient intakes.

Blinding used

Not Applicable


Not Applicable 

Statistical Analysis

  • Data are given as the mean ± Standard deviation
  • The normal distribution of variables was examined with Shapiro-Wilk’s test and non-normally distributed variables were log transformed
  • The group differences were tested for significance using a repeated measures one way ANOVA  followed by Tukey’s test or the non parametric Kruskal-Wallis test followed by the Mann-Whitney’s U test adjusted with the Bonfferoni test
  • Logistic regression analysis were carried out to estimate the risks of abdominal obesity and metabolic syndrome, and a standardized (SD=1.0) odds ratio (OR) was calculated
  • Correlation coefficients were determined by single or multiple linear regression analysis. P<0.05 was considered to indicate statistical significance.
Data Collection Summary:

Timing of Measurements

Not Applicable

Dependent Variables

  • Abdominal obesity
  • Metabolic syndrome risk factors (lipid profile; glucose, insulin, HbA1c)
  • Lipogenic index
  • Desaturase activity (D5D, D9-16D, D9-18D, d6D)
  • Metabolic syndrome risk.

Independent Variables

  • Energy
  • Macronutrient and fatty acids intakes and quality of fats and fatty acids composition
  • Plasma fatty acids including lipogenic acid in plasma cholesteryl esters
  • Adiponectin
  • Leptin.


Description of Actual Data Sample:
  • Initial N: 187 males
  • Attrition (final N): 94 participants
  • Age:
    • MS: 50.4±6.1
    • OB: 51.0±5.6
    • Control: 49.3±6.6 years
  • Ethnicity: Japanese
  • Other relevant demographics: Energy, macronutrient and fatty acids intakes; medical history
  • Anthropometrics:
    • BMI
    • Waist circumference
  • Location: Nara Health Promotion Center, Japan.


Summary of Results:

Key Findings

  • BMI, waist circumference, triacylglycerol, fasting blood glucose, blood insulin, HbA1c, HOMA-IR and leptin were significantly higher and HDL-C was lower in the OB group than the control group
  • The MS group had higher levels of triacylglycerol, fasting blood glucose and HbA1c than the OB group
  • Systolic blood and diastolic blood pressure were significantly higher in the MS group than the control and OB groups
  • There was no significant difference in fatty acid composition compared with the control group
  • The levels of palmitoleic, oleic and gamma linolenic acids were higher and the level of linoleic acid was lower in the MS group than the control group
  • Higher levels of D6D activity and lower levels of D5D activity were also significantly higher in the MS group than the control or OB group
  • The lipogenic index was significantly higher in the MS group than the control group
  • No significant difference was observed in energy, macro nutrient and fatty acids intakes across the control, OB and MS groups
  • The risk of developing abdominal obesity among no-obese controls increased with a lower level of D5D activity (OR=0.39, P<0.01)
  • Greater D9-16D activity increased the risk of developing metabolic syndrome from abdominal obesity (OR=2.44, P<0.01)
  • In the multiple linear regression analysis, D5D activity positively correlated with the intake of eicosapentaenoic acid (EPA).
  • For each SD increase in D5D activity there was a decrease of roughly 60% in the risk of developing abdominal obesity
  • For D9-16D activity, the situation was opposite, with a 2.4 fold increase in the risk of developing metabolic syndrome
  • D5D activity inversely correlated with waist circumference, LDL cholesterol, blood insulin, HbA1c, HOMA-IR and leptin level while it positively correlated with HDL cholesterol and the intake of n-3 PUFA, eicosapentaenoic acid and docosahexaenoic acid
  • D9-16D activity positively related with waist circumference, the serum triacylglycerol level and the lipogenic index.



Author Conclusion:
  • These results suggest that estimated D5D and D9-D16D activities can be used to predict abdominal obesity and metabolic syndrome
  • The risk of developing abdominal obesity dropped by 60% for each SD increase in D5D activity and the risk of developing metabolic syndrome from abdominal obesity increased 2.4 times for each SD increase in D9-D16D activity
  • In the multiple linear regression models D5D and D9-16D positively correlated with the intake of EPA and lipogenic index respectively
  • These results suggest that the intake of EPA is beneficial to prevent abdominal obesity and the development of metabolic syndrome.


Funding Source:
Government: Grants – in-aid for scientific research from the ministry of education, culture, sports, science and technology of Japan
University/Hospital: Grants from Nara women’s University
Reviewer Comments:
  • Study is non-randomized control trial. Based on the diagnostic criteria of metabolic syndrome subjects were divided into groups and compared with a control group (no metabolic syndrome risk factors). Results are very promising and suggest that estimated D5D and D9-D16D activities can be used to predict abdominal obesity and metabolic syndrome. This study was reported only in males. An association of EPA in reducing metabolic syndrome risk factors were observed.
  • However, further double-blind randomized controlled clinical trails are required to study the effect of EPA and its association with D5D and D9-16D activities in relation to metabolic syndrome risk factors in different population and races.
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? ???
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? N/A
  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? No
  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? 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? 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.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  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? 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? N/A
  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? 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? 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? N/A
  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? N/A
  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