Self-reported assessment methods present difficulties for determining accurate dietary consumption. Stable isotope analysis of biomarkers can greatly improve the accuracy of dietary intake assessments. This objective approach eliminates subject bias by combining mass spectrometry with dietary biomarkers. Foods and waters consumed have unique carbon-13, nitrogen-15, oxygen-18 and deuterium fingerprints that can be utilized as dietary biomarkers when sampled in blood, breath, urine or feces.
We present several applications below of stable isotope dietary biomarkers. A good reference for dietary biomarkers was written by Hedrick et al.
Carbon Isotope Biomarkers for Dietary Sugar
Many epidemiologic studies have shown increased consumption of corn-based sweeteners, for example products made with fructose corn syrup. Certain plants such as corn, called C4 plants, extract heavier 13CO2 from the atmosphere and convert it into carbohydrates via the Hatch-Slack cycle. Sugars derived from corn are naturally higher in carbon-13. When corn sugars are ingested, they result in elevation of 13C in the body.
Various biomarkers have been evaluated to assess dietary sugar intake including serum (total 13C carbon), plasma 13C-glucose, breath 13CO2, and plasma 13C-alanine. Glucose, alanine and breath reflect short-term dietary sugar levels, whereas total 13C carbon in serum and red blood cells reflect longer-term consumption levels.
Nitrogen Isotope Biomarkers for Meat and Fish Intake
Schoeller et al. measured the 15N content of the diet typically found in metropolitan Chicago, IL (Ecology of Food and Nutrition 18:159-170, 1986). Meat and pork contained higher 15N levels than fruits and vegetables. Fish contained the highest levels. Kuhnle et al. showed significant 15N differences in urine and feces of subjects eating meat or fish diets. Subjects received for 8 days either a meat, fish or meat and fish diet. The study concludes that 15N levels in urine and feces are suitable candidate biomarkers for short-term meat and fish intake. Red blood cells (RBC) are more suitable for long-term intake of meat and fish. In fact, O’Brien et al. observed that 15N levels are a biomarker for omega-3 (n-3) fatty acids derived from fish.