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Providing perspectives on recent research into vitamins and nutritionals


Annual Physical Examinations: Do MDs ask for a Food Frequency Questionnaire or a Blood Lipid Panel?

By Michael McBurney

In the field of nutrition, dietary intake is more often assessed using food frequency questionnaires (FFQ) or 3-day food records than biological markers. FFQs are used for convenience and because they cost less and are less invasive than venipuncture. FFQs are only valuable when validated against the gold standard – nutrient status assessed using biological markers.

Allaire and colleagues compared a self-administered web-based FFQ against an interviewer-administered FFQ, 3-day food records, and biological samples collected from 60 men participating in a clinical trial (50% of total study participants). The men were 60 years of age with a mean body mass index of 27.

The authors state, “Correlations were not significant between nuts and vegetable oil intakes and the proportion of ALA (α-linoleic acid), their main source in the diet, in the RBC membranes. Nevertheless, margarine intake was correlated with ALA proportions in the RBC membranes.” It can be seen from Supplementary Table S3 that only 2 of 18 correlations were statistically significant between food groups and RBC fatty acid concentrations. With 10% of comparisons being statistically significant, there may also be a risk of erroneous conclusions being drawn from too many statistical tests.

Spearman correlation coefficients between web-based FFQ and RBC fatty acids were statistically significant for total omega-3, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) concentrations in RBC but not α-linolenic acid (ALA), docosapentaenoic acid (DPA), total omega-6 fatty acids, linoleic acid (LA) or arachidonic acid (AA).

Advances in food technology have made it possible to alter the fatty acid content of almost any food product. Dairy products can contain EPA+DHA. There are low-fat cheeses. Without accurate food composition datasets with information on specific products (and brands), it is difficult to determine omega-3 intake from dietary records using a limited number of foods listed in a FFQ. Indeed, self-reported information on the number of fish oil capsules being consumed does not correlate with plasma EPA+DHA concentrations.

The average omega-3 index of these men was 5.2% (% of total RBC fatty acids). This is considerably lower than the 8% target recommended for cardiovascular protection and below baseline values (7%) of German adults whose omega-3 index increased to >11.5%  after consuming ≥670 mg EPA+DHA daily for 6 months.

While self-reported dietary intake data may not accurately reflect cellular concentrations of omega-3 fatty acids, having a low omega-3 index should be addressed.  Low omega-3 index is associated with sudden cardiac arrest and postpartum depression. When choosing a product (food or dietary supplement) to increase your omega-3 index, look for the quantity (milligrams) of EPA and DHA per serving.

Physicians measure blood pressure and blood cholesterol concentrations rather than dietary sodium and fat intake of their patients. RBC omega-3 index should be added to the list of biological markers to be monitored.

Main Citation

Allaire J, Moreel X, Labonte M-E, Leger C, Caron A, Julien P, Lamarche B, Fradet V. Validation of the omega-3 fatty acid intake measured by a web-based food frequency questionnaire against omega-3 fatty acids in red blood cells in men with prostate cancer. 2015 EJCN doi: 10.1038/ejcn.2015.7

Other Citations

Harris WS, von Schacky C. The omega-3 index: a new risk factor for death from coronary heart disease? 2004 Prev Med doi: 10.1016/j.ypmed.2004.02.030

Neubronner J, Schuchardt JP, Kressel G, Merkel M, von Schacky C, Hahn A. Enhanced increase in omega-3 index in response to long-term n-3 fatty acid supplementation from triacylglycerides versus ethyl esters. 2010 EJCN doi: 10.1038/ejcn.2010.239

Gurbel PA, Bliden K, Ranzese C, Gesheff M, Kasa H, Tantry U, Harris W. Disconnect between reported fish oil capsule intake and plasma omega-3 fatty acid levels. 2015 JACC doi: 10.1016/S0735-1097(15)61632-1

Aarstoey H, Aarsetoey R, Lindner T, Staines H, Harris WS, Nilsen DWT. Low levels of the omega-3 index are associated with sudden cardiac arrest and remain stable in survivors in the subacute phase. 2011 Lipids doi: 10.1001/s11745-0101-3511-3

Markhus MW, Skotheim S, Graff IE, Froyland L, Braarud HC, Stormak KM, Malde MK. Low omega-3 index in pregnancy is a possible biological risk factor for postpartum depression. 2013 PLoS ONE doi: 10.1371/journal.pone.0067617