Apple intake biomarkers: phloretin in urine shows promise
What it found
In people, urinary phloretin and its glucuronide were the most promising markers of recent apple intake.
The authors say more validation work is needed before levels can be translated into how much apple was eaten.
What they found
Studies in people
Phloretin in urine
Urinary excretion of phloretin and phloretin glucuronide were the most promising markers of recent apple intake. These compounds come from phloridzin and phloretin 2'-O-xyloglucoside, which are characteristic of apples.
Dose response in people
In a 4-week cross-over study with 30 subjects, urinary phloretin reflected the 1.5-fold difference in phloretin content between two apple varieties. Another short-term study with 30 healthy volunteers found significantly different urine phloretin after low, medium and high apple doses.
Short half-life
Phloretin is rapidly excreted, with a maximum at 3 plus or minus 1 hour, and 24 hours after apple intake the increase was no longer detectable. This means it reflects recent intake, not long-term consumption.
Low plasma levels
After eating 1 kg of apples, the maximum phloretin concentration in men was 12.1 plus or minus 6.6 nmol/L. The authors say this is very low and may be hard to measure for low to moderate apple intakes.
Studies in people and animals
Pear and stone fruit
For pear, arbutin and hydroquinone sulfate were possible markers but data are scarce. For stone fruit, no candidate biomarker could be identified from the literature.
Other findings
Apple products
Phloretin and its glucuronide are also associated with apple cider intake. Apple processing affects these compounds: only 10 to 20 percent of the original dihydrochalcone content is recovered in apple juice.
What the authors conclude
“To conclude, the urinary excretion of phloretin glucuronide or of phloretin measured after sample hydrolysis can be considered as the most promising specific biomarker of apple intake.”
Also in their conclusions
- They conclude that urinary phloretin glucuronide or phloretin measured after sample hydrolysis can be considered as the most promising specific biomarker of apple intake.
- They state that more validation work is needed before its level can be translated into a value, or more likely a value range, of apple consumption.
- They advise that the time window for urine collection and the dose-response relationships should notably be further documented.
How it was done
The authors wanted to find reliable markers of apple intake because dietary questionnaires are prone to overestimation and traditional biomarkers like vitamin C and carotenoids are not accurate enough to reflect individual intakes.
They systematically searched the literature for studies on biomarkers of pome and stone fruit intake. For apple, they found 14 papers: five observational studies, seven single-dose studies, and two 4-week intervention studies that reported associations between apple intake and metabolites in plasma, urine or ileostomy fluid.
What it can’t tell you
- This is a review of existing studies, so it cannot show cause and effect.
- The studies included were small, with 6 to 30 participants, so the findings may not apply to everyone.
- The authors note that inter-individual variation in absorption and metabolism of these compounds still needs to be evaluated.
Who paid
- Conflicts
- Not applicable.Not applicable.The authors declare that they have no competing interests.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
- Authors work at
- 1Research and Innovation Centre Food Quality and Nutrition, Italy; Université Clermont Auvergne, France; University of Copenhagen, Denmark
The paper
- Title
- Food intake biomarkers for apple, pear, and stone fruit
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Ulaszewska M, Vázquez-Manjarrez N, Garcia-Aloy M, et al (2018). Food intake biomarkers for apple, pear, and stone fruit. Genes & nutrition. doi:10.1186/s12263-018-0620-8Free full textPubMed 30519365DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error