Table of Contents

Component Description

Trans fatty acids are unsaturated fatty acids that contain at least one double bond in the trans configuration. The three-dimensional structure of trans fatty acids is more similar to saturated fatty acids than to regular unsaturated fatty acids, which have their double bond in the cis configuration. The trans configuration substantially alters the physical properties of the fatty acids, and thus the properties of the oil containing these trans fatty acids for cooking and food manufacturing. Also, it substantially alters the biologic and health effects of the fatty acids when consumed.

A positive linear trend between trans fatty acid intake, and total and LDL cholesterol concentration were established, which links elevated trans fatty acids in blood with increased risk of coronary heart diseases. The Institute of Medicine recommended that ‘trans fatty acid consumption be as low as possible while consuming a nutritionally adequate diet’.

In addition, the Dietary Guidelines for Americans, 2000 and guidelines from the National Cholesterol Education Program (NCEP), were similar with recommendations to limit trans fat intake in the diet. In 2003, FDA amended its regulations on nutrition labeling to require that trans fatty acids be declared in the nutrition label of conventional foods and dietary supplements. This rule is intended to provide information to assist consumers in maintaining healthy dietary practices.

Eligible Sample

Examined participants aged 3 years and older were eligible. This dataset contains data for eligible participants aged 20 years and older in the morning (AM) session.

Participants 3-19 years will be released at a later date.

Description of Laboratory Methodology

The trans fatty acids procedure determines the total (free and esterified) content of selected trans fatty acids in plasma and provides results in concentration units, as well as percent units (trans fatty acids as percent of total fatty acids).

The fatty acids in plasma are converted into free fatty acids by subsequent acidic and alkaline hydrolysis. The free fatty acids are extracted from the sample solution using liquid-liquid extraction and derivatized with pentafluorobenzylbromide (PFB-Br). The derivatized fatty acids are separated by capillary gas chromatography and detected by mass spectrometry using negative chemical ionization. 

The fatty acids are identified based on their chromatographic retention time and on the specific mass to charge ratio of the ion formed in the ion source. Retention times are compared against those obtained with known standards. Quantitation is performed with standard solution using stable isotope-labeled fatty acids as internal standards.

Refer to the Laboratory Method Files section for detailed laboratory procedure manual(s) of the methods used.

Trans fatty acids are a new component in the 2009-2010 cycle.

Laboratory Method Files

trans Fatty Acids (April 2016)

Laboratory Quality Assurance and Monitoring

Plasma specimens were processed, stored and shipped to Divisions of Laboratory Services, Centers for Disease Control, Atlanta, GA for analysis.

Detailed instructions on specimen collection and processing are discussed in the NHANES Laboratory Procedures Manual (LPM). Vials are stored under appropriate frozen (–20°C) conditions until they are shipped to National Center for Environmental Health for testing.

The NHANES quality assurance and quality control (QA/QC) protocols meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES) Laboratory Procedures Manual (LPM).

Mobile Examination Centers (MECs)
Laboratory team performance is monitored using several techniques. NCHS and contract consultants use a structured quality assurance evaluation during unscheduled visits to evaluate both the quality of the laboratory work and the quality-control procedures. Each laboratory staff person is observed for equipment operation, specimen collection and preparation; testing procedures and constructive feedback are given to each staff. Formal retraining sessions are conducted annually to ensure that required skill levels were maintained.

Analytical Laboratories
NHANES uses several methods to monitor the quality of the analyses performed by the contract laboratories. In the MEC, these methods include performing blind split samples collected on “dry run” sessions. In addition, contract laboratories randomly perform repeat testing on 2.0% of all specimens.

NCHS developed and distributed a quality control protocol for all the contract laboratories which outlined the Westgard rules (Westgard et al, 1981) used when running NHANES specimens. Progress reports containing any problems encountered during shipping or receipt of specimens, summary statistics for each control pool, QC graphs, instrument calibration, reagents, and any special considerations are submitted to NCHS quarterly. The reports are reviewed for trends or shifts in the data. The laboratories are required to explain any identified areas of concern.

All QC procedures recommended by the manufacturers were followed. Reported results for all assays meet the Division of Laboratory Sciences’ quality control and quality assurance performance criteria for accuracy and precision, similar to the Westgard rules (Westgard et al, 1981).

Data Processing and Editing

The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.

Analytic Notes

Refer to the 2009-2010 Laboratory Data Overview for general information on NHANES laboratory data.

Subsample weights
Measures of trans fatty acids were measured in a fasting morning sample of persons 20 years and over. Special fasting sample weights are required to analyze these data properly. Specific sample weights for this sample are included in this data file and should be used when analyzing these data.

Demographic and Other Related Variables
The analysis of NHANES laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2009-2010 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample design variables. The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively) in the demographic data file.

The Fasting Questionnaire File includes auxiliary information such as fasting status, the time of venipuncture, and the conditions precluding venipuncture.

Links to NHANES Data Files
This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier SEQN.

Detection Limits
The detection limits were constant for all of the analytes in the data set. All results were at or above the lower detection limit.

The lower limits of detection (LLOD, in µmol/L) for trans fatty acids are:

Variable Name  SAS Label  LLOD 
 LBXHDT  trans-9-hexadecenoic acid (µmol/L)  0.07
 LBXOD9  trans-9-octadecenoic acid(µmol/L)  0.28
 LBXOD1  trans-11-octadecenoic acid(µmol/L)  0.43
 LBXOTT  trans-9,12-octadecadienoicacid(µmol/L)  0.02

Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues.

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number.
Target:
Both males and females 20 YEARS - 150 YEARS

WTSAF2YR - Fasting Subsample 2 Year MEC Weight

Variable Name:
WTSAF2YR
SAS Label:
Fasting Subsample 2 Year MEC Weight
English Text:
Fasting Subsample 2 Year MEC Weight
Target:
Both males and females 20 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 337218.92036 Range of Values 2926 2926
. Missing 0 2926

LBXHDT - trans 9-hexadecenoic acid (umol/L)

Variable Name:
LBXHDT
SAS Label:
trans 9-hexadecenoic acid (umol/L)
English Text:
trans 9-hexadecenoic acid concentrate (C16:1 t9) (uM)
Target:
Both males and females 20 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.88 to 33.1 Range of Values 2574 2574
. Missing 352 2926

LBXOD1 - trans 11-octadecenoic acid (umol/L)

Variable Name:
LBXOD1
SAS Label:
trans 11-octadecenoic acid (umol/L)
English Text:
trans 11-octadecenoic acid (C18:1 t11)
Target:
Both males and females 20 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
2.92 to 161 Range of Values 2575 2575
. Missing 351 2926

LBXOD9 - trans 9-octadecenoic acid (umol/L)

Variable Name:
LBXOD9
SAS Label:
trans 9-octadecenoic acid (umol/L)
English Text:
trans 9-octadecenoic acid (C18:1 t9)
Target:
Both males and females 20 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
2.66 to 127 Range of Values 2578 2578
. Missing 348 2926

LBXOTT - trans-9, trans-12-octadecadienoic acid

Variable Name:
LBXOTT
SAS Label:
trans-9, trans-12-octadecadienoic acid
English Text:
trans 9, trans 12-octadienoic acid (C18:2 t9, 12) (umol)
Target:
Both males and females 20 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.416 to 15.1 Range of Values 2467 2467
. Missing 459 2926