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.

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