The CARO Study – Bioefficacy of Beta-Carotene in Oil and in a Mixed Diet in Healthy Subjects


A controlled dietary intervention study will be carried out based on the stable isotope method the investigators have developed to quantify both the absorption of beta-carotene and its bioconversion to retinol in oil and in a mixed diet. For 6 weeks the participants will consume 2 capsules/day, 7 days/week with each capsule containing 50-mg [13C10] beta-carotene and 50-mg [13C10] retinyl palmitate. For three weeks they will consume a diet with high levels of beta-carotene in vegetables and fruits and for the other 3 weeks they will consume a diet with low levels of beta-carotene in vegetables and fruits supplemented with an extra amount of beta-carotene in oil. Samples of blood and faeces will be taken. The study hypothesis is that the absorption of beta-carotene in oil in comparison with the absorption of beta-carotene in a mixed diet differs by a factor of 3 to 6. The investigators want to measure the influence of the food matrix of vegetables and fruits on the absorption of beta-carotene in healthy humans on a western diet.

Full Title of Study: “Bioefficacy and Bioavailability of Beta-Carotene in Oil and in a Mixed Diet in Healthy Subjects Measured Using Specifically 13C-Labelled Beta-Carotene and Retinol”

Study Type

  • Study Type: Interventional
  • Study Design
    • Allocation: Randomized
    • Intervention Model: Crossover Assignment
    • Primary Purpose: Prevention
    • Masking: None (Open Label)


  • Behavioral: absorption and conversion of beta-carotene in human gastrointestinal (GI) tract

Clinical Trial Outcome Measures

Primary Measures

  • levels of retinol and carotenoids and the degree of isotopic enrichment in serum (fasting blood sample) and in faeces (72 hour collection) at the start and at the end of each of the 3-week periods

Participating in This Clinical Trial

Inclusion Criteria

  • Men and women between 18 and 50 years old – Body mass index (BMI) between 18 and 25 kg/m2 – Willing to consume the controlled diet and not consume other food items – Willing to consume the cooked meal at the research facility and the bread meals and snacks at home (distributed to the participants) – Willing to consume the capsules every day Exclusion Criteria:

  • Hematological diseases and chronic diseases including cancer, renal insufficiency, liver disease, diagnosed gastrointestinal disorders, or surgery of the gastrointestinal tract – Use of (oral) drugs suspected of interfering with fat-soluble-vitamin absorption – Smoking – Excessive alcohol consumption (>30 g/d) – Consumption of vitamin or carotenoid supplements 6 weeks before and during the study – Not too low or high levels of serum beta-carotene and retinol – Normal hemoglobin, hemocytometry, creatinine, ALAT, alkaline phosphatase, and cholesterol blood values (compared with laboratory references) – Pregnancy

Gender Eligibility: All

Minimum Age: 18 Years

Maximum Age: 50 Years

Are Healthy Volunteers Accepted: Accepts Healthy Volunteers

Investigator Details

  • Lead Sponsor
    • Radboud University Medical Center
  • Collaborator
    • Dutch Dairy Organization (NZO)
  • Overall Official(s)
    • Ton HJ Naber, MD PhD, Study Director, Radboud University Medical Center
    • Clive E West, PhD DSc, Principal Investigator, Radboud University Medical Center
    • Carolien A Bouwman, MSc, Study Chair, Radboud University Medical Center


van Lieshout M, West CE, Muhilal, Permaesih D, Wang Y, Xu X, van Breemen RB, Creemers AF, Verhoeven MA, Lugtenburg J. Bioefficacy of beta-carotene dissolved in oil studied in children in Indonesia. Am J Clin Nutr. 2001 May;73(5):949-58.

van Lieshout M, West CE, van Breemen RB. Isotopic tracer techniques for studying the bioavailability and bioefficacy of dietary carotenoids, particularly beta-carotene, in humans: a review. Am J Clin Nutr. 2003 Jan;77(1):12-28. Review.

West CE, Eilander A, van Lieshout M. Consequences of revised estimates of carotenoid bioefficacy for dietary control of vitamin A deficiency in developing countries. J Nutr. 2002 Sep;132(9 Suppl):2920S-2926S. doi: 10.1093/jn/132.9.2920S.

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