Biomarkers for Fruit and Vegetable Intake: A Review

A new narrative review in Nutrition Bulletin evaluates candidate biomarkers for estimating dietary intakes of fruits and vegetables, highlighting both strengths and weaknesses of current methods.

Overview

The review assesses several biomarkers, including urinary potassium, flavonoids, hippuric acid, serum and erythrocyte folate, serum vitamin C, and blood and skin carotenoids. No single biomarker is currently ready for individual-level assessment, though combined panels may improve group-level estimates.

Biomarker Strengths and Weaknesses

Urinary Potassium

• Correlates with vegetable intake but not consistently with fruit intake
• Affected by medications, diseases, and hormones
• Requires 24-hour urine collection

Urinary Flavonoids

• Promising for measuring recent intake
• Not exclusive to fruits and vegetables — also influenced by tea, chocolate, coffee, spices, and wine

Urinary Hippuric Acid

• Shows dose-dependent associations with fruit and vegetable intake
• Most studies conducted in children and adolescents only

Serum and Erythrocyte Folate

• Serum folate reflects short-term intake; erythrocyte folate reflects long-term intake
• Not exclusive to fruits and vegetables
• Influenced by supplements, fortified foods, demographics, and lifestyle

Serum Vitamin C

• Reflects dietary intake but saturates at 200–400 mg
• Limited sensitivity at high intakes
• Useful primarily in populations with low supplementation

Blood Carotenoids

• Considered the best biomarker by the Institute of Medicine
• Responsive to both short- and long-term intake
• Invasive sampling required
• Some fruits and vegetables are low in carotenoids
• Interlaboratory reproducibility needs further study

Skin Carotenoids

• Noninvasive alternative to blood carotenoids
• Requires further validation in diverse populations

Short-Term vs. Habitual Intake Biomarkers

Short-term biomarkers:

• Serum vitamin C, serum folate, urinary hippuric acid, urinary potassium, urinary flavonoids

Habitual intake biomarkers:

• Blood and skin carotenoids, erythrocyte folate

Conclusions

• No single biomarker is ready for individual-level assessment
• Combined biomarker panels may improve group-level estimates but need further validation
• Standardization and validation in diverse populations are required

The review underscores that while progress has been made, much work remains before these tools can be reliably used to assess fruit and vegetable intake at the individual level.