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

Study Design:
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Quality Rating:
Research Purpose:

To examine the association of nutrient intakes with metabolic syndrome in a Japanese descendant population at high risk for metabolic abnormalities.

Inclusion Criteria:
  • Japanese-Brazilian population living in Baura, Sao Paulo, Brazil
  • Entire Japanese-Brazilian population at least 30 years of age (N=1,651) was invited and 1,330 first-generation (Japan-born) and second-generation (Brazil-born) subjects participated in all phases of the survey.
Exclusion Criteria:

Self-reported diabetes, hypertension, dyslipidemia and other diseases whose treatment could interfere in the dietary plan.


Description of Study Protocol:


  • The entire Japanese-Brazilian population over age 30 was invited
  • Recruitment methodology was not described.


Cross-sectional survey.

Statistical Analysis

  • SPSS, version 10.0 (Chicago, IL) was used in the statistical analysis
  • Regression model was used in energy-adjusted nutrient intakes
  • Student's T-test was used in nutritional, clinical and lab data
  • Mantel-Haenszel Chi-square was used for categorical data
  • Logistic regression was used to calculate the odds ratios (ORs) and confidence intervals for metabolic syndrome
  • ORs were adjusted for sex, age, smoking, physical activity, level of education, total energy, total fiber and alcohol
  • Statistical significance was defined as a two-tailed P-value of <0.05.
Data Collection Summary:

Timing of Measurements

  • One-time baseline survey of measurements and demographic information
  • Screened study participants who took part in the survey were interviewed at home by a trained interviewer, using standardized questionnaires and they were scheduled for physical examinations and lab procedures after overnight fasting.

Dependent Variables

Diagnosis of metabolic syndrome was based on National Cholesterol Education Program Adult Treatment Panel III, replacing the anthropometric cutoffs by those previously proposed by the World Health Organization for Asians.  

Independent Variables

Dietary data: A quantitative food frequency questionnaire was used, which was developed and validated for the Japanese-Brazilian population,

  • Questions included usual composition of foods and food groups eaten last year (122 items)
  • Habitual frequency of consumption of each food item
  • Size of usual portion
  • Questions concerning use of sauces, intake of visible fat, type of fat used in cooking
  • Nutrient compositions were then calculated by Dietsys 4.01 software
  • Variables of interest: Total calories, protein, fat and type of fat, cholesterol, total fiber and alcohol
  • Macronutrients were calculated in total calories and percentages.

Control Variables

  • Nutrient intake was adjusted for total energy intake
  • Sex
  • Age
  • Smoking
  • Generation
  • Leisure physical activity: Assessed by questionnaire items including types of physical activity and attributes
  • Level of education
  • Dietary fiber
  • Alcohol intake.
Description of Actual Data Sample:
  • Initial N: 877 (47%, 412 men and 53%, 465 women)
  • Attrition (final N): As above
  • Age: Men,  55.7±12.7 years; women, 54.4±11.9 years
  • Ethnicity: Japan-Brazilian population
  • Other relevant demographics: Sub-groups had similar demographic characteristics
  • Anthropometrics: Individuals within and between the sub-groups (men vs. women, metabolic syndrome and no metabolic syndrome) appeared to have similar anthopometric findings
  • Location: Bauru, Sao Paulo, Brazil.
Summary of Results:


  • Slightly higher prevelance of of metabolic syndrome was found in men [49.8% (95% CI, 44.8 to 54.6)] than in women [43.0% (95% CI, 38.4 to 47.6)]
  • Men with metabolic syndrome had significantly higher total fat, oleic acid and cholesterol intakes than those without metabolic syndrome (P<0.05)
  • Men with metabolic syndrome showed higher cholesterol intake (233.2±116.3g vs. 211.7±5.8g per day, P<0.05) and lower carbohydrate intake (288.5±45.8g vs. 300.1±39.8g per day, P<0.001) than those without metabolic syndrome. No difference was observed among women.
  • ORs of metabolic syndrome across quintiles of dietary nutrients showed that the highest quintile of total fat was associated with a five-fold increase in risk of having metabolic syndrome, after adjusting for the confounders (OR, 5.0; 95% CI, 1.58 to 16.00; P<0.005)
  • The highest consumption of linoleic acid was associated with a protection against metabolic syndrome (OR, 0.50; 95% CI, 0.26 to 0.98; P<0.05)
  • After adjustment for confounders, only fried food intake, compared to the other food groups, was shown to be associated with increased risk of metabolic syndrome [OR, 1.27 (95% CI, 0.82 to 1.96), 1.42 (0.92 to 2.19), 1.31 (0.85 to 2.04) and 1.69 (1.10 to 2.61)] for the second, third, fourth and fifth quintiles, respectively (P=0.02).
Author Conclusion:
  • The authors suggest that a total fat intake may be a risk factor for metabolic syndrome in the Japanese-Brazilian population
  • Secondly, the authors suggest a possible beneficial effect from polyunsaturated fatty acids such as linoleic acid, which may reduce the risk of clustering of diseases linked by insulin resistance.
Funding Source:
Other: Fundacao de Amparo a Pesquisa do Estado de Sao Paulo
Reviewer Comments:
  • Well planned survey
  • Limitation noted by the authors: Food frequency techniques could be considered limited by their lack of quantitative accuracy.
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? 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")? 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? 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? 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.) N/A
  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? 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? 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? 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)? 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? 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