Establishing conclusive links between intake patterns and disease/health states is contingent upon an accurate assessment of food and nutrient intakes.  Random errors and reporting bias limit the reliability of self-reported dietary intakes, and although some biomarkers are becoming more effective, they typically only reflect short term intakes and are subject to their own errors.  One biomarker type that may have stronger dietary associations and stability over time is natural abundance stable isotope ratios (NIR).  Recently nitrogen isotope ratios have been used to estimate intake of animal foods, but there are limitations when it is used to differentiate between different animal foods.  Johnson and colleagues conducted a study designed to refine the use of NIR as a biomarker and report their results in the September 2022 issue of The Journal of Nutrition.

Subjects included men enrolled in a 12 week inpatient dietary intervention study.  They were assigned to one of eight groups that received diets that varied in their level (presence/absence) of fish, meat, and sugar sweetened beverages.  Fasting blood was drawn before and after the interventions, and plasma was used to measure the NIR of amino acids (NIRAAs).

Fish and meat intake led to an increase in plasma NIRAAs for most amino acids, but the increase in NIRLeucine was greatest with fish intake.  In contrast, NIRThreonine was decreased by the intake of both fish and meat.  Red blood cell NIRAAs were less likely to increase with fish intake, and only red blood cell NIRProline increased with meat intake.  Plasma and red blood cell NIRAAs were not affected by intake of sugar sweetened beverages.  The results led the authors to conclude that plasma and red blood cell NIRAAs were associated with fish and meat intakes, but provided no additional benefit in identifying intake of these foods above that obtained for whole-tissue stable isotope biomarkers.

In an editorial, Kuhnle describes one of the benefits of stable isotope ratios to estimate food/nutrient intakes is that they are based on intrinsic aspects of metabolism, meaning they reflect the origin of foods, the enzymatic activities incorporating them, and that they are less affected by food processing.  Kuhnle states these factors make stable isotope ratios an ideal complement to other dietary assessment methods, but that more work is needed to identify their strengths and weaknesses.


Jessica J Johnson, Pamela A Shaw, Matthew J Wooller, Colleen A Venti, Jonathan Krakoff, Susanne B Votruba, Diane M O’Brien, Amino Acid Nitrogen Isotope Ratios Respond to Fish and Meat Intake in a 12-Week Inpatient Feeding Study of Men, The Journal of Nutrition, Volume 152, Issue 9, September 2022, Pages 2031–2038,

Gunter G C Kuhnle, From Rough Diamond to Polished Gem, The Journal of Nutrition, Volume 152, Issue 9, September 2022, Pages 2009–2010,

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