Biomarkers are Best Indicators of Nutritional Status
Short and sweet. Accurate nutritional assessment requires blood sampling (until other less-invasive measures are developed). Self-reported dietary intake instruments are poorly, in statistical terms the term would be ‘weakly’, correlated with blood biomarkers.
Lassale and colleagues asked 198 adult volunteers complete dietary records on 3 non-consecutive days. Two blood samples were taken 3 weeks apart to measure plasma concentrations of vitamin C, β-carotene, and omega-3 fatty acids – eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and eicosapentaenoic acid (EPA).
The adjusted correlations between food group reported intake and biomarker status are weak – statisticians define a weak correlation as an r<0.5. With the exception of vitamin C (r=0.58) and DHA (r=0.45) in men, adjusted correlations between reported nutrient intake and biomarker status were r≤0.38. This means that <14% of the total variation in the relationship can be explained. Abysmal.
The men and women living in France report consuming >250 mg DHA daily, at the lower end recommended by EFSA Panel on Dietetic Products, Nutrition and Allergies. Unfortunately, total plasma fatty acid concentrations are not reported so an omega-3 index cannot be calculated. However, plasma omega-3 concentrations for EPA 5-5.5 mg/dL (166-182 µmol/L), DPA 1.8-1.9 mg/dL (54-58 µmol/L), and DHA 8.5-10.5 mg/dL (259-320 µmol/L) represent ≥90th percentile for American adults 20 years and older for EPA (Table 2.33.a.2), DPA (Table 2.35.a.2), and DHA (Table 2.37.a.2).
These men and women living in France have more omega-3 fatty acids and beta-carotene in circulation than Americans. Plasma vitamin C concentrations were similar to those reported in Americans 6y and older, ~ 1mg/dL (56.8 µmol/L). In both France and the U.S., reported intake of fruit and vegetables is far short of recommendations.
The lack of relationship between reported dietary intake and biomarkers affirms evidence that trial participants may not provide accurate information to researchers. Measuring biomarkers should be encouraged as it provides more accurate information on biomarkers.
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Scientific Opinion on the Tolerable Upper Intake Level of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA). 2012 EFSA J doi: 10.2903/j.efsa.2012.2815
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