British Journal of Nutrition

Research Article

Influence of feeding different vegetables on plasma levels of carotenoids, folate and vitamin C. Effect of disruption of the vegetable matrix

Karin H. van het Hofa1 c1, Lilian B. M. Tijburga1, K. Pietrzika2 and Jan A. Weststratea1

a1 Unilever Research Vlaardingen, PO Box 114, 3130 AC Vlaardingen, The Netherlands

a2 Department of Pathophysiology of Human Nutrition, University of Bonn, Bonn, Germany

Abstract

Carotenoids, folate and vitamin C may contribute to the observed beneficial effects of increased vegetable intake. Currently, knowledge on the bioavailability of these compounds from vegetables is limited. We compared the efficacy of different vegetables, at the same level of intake (i.e. 300 g/d), in increasing plasma levels of carotenoids, folate and vitamin C and we investigated if disruption of the vegetable matrix would enhance the bioavailability of these micronutrients. In an incomplete block design, sixty-nine volunteers consumed a control meal without vegetables and three out of four vegetable meals (i.e. broccoli, green peas, whole leaf spinach, chopped spinach; containing between 1·7 and 24·6 mg β-carotene, 3·8 and 26 mg lutein, 0·22 and 0·60 mg folate and 26 and 93 mg vitamin C) or a meal supplemented with synthetic β-carotene (33·3 mg). Meals were consumed for 4 d and fasting blood samples were taken at the end of each period. Consumption of the spinach-supplemented meal did not affect plasma levels of β-carotene, although the β-carotene content was 10-fold those of broccoli and green peas, which induced significant increases in plasma β-carotene levels (28 (95 % CI 6·4, 55) % and 26 (95 % CI 2·6, 54) % respectively). The β-carotene-supplemented meal increased plasma concentrations of β-carotene effectively (517 (95 % CI 409, 648) %). All vegetable meals increased the plasma concentrations of lutein and vitamin C significantly. Broccoli and green peas were, when expressed per mg carotenoid consumed, also more effective sources of lutein than spinach. A significant increase in plasma folate concentration was found only after consumption of the spinach-supplemented meal, which provided the highest level of folate. Disruption of the spinach matrix increased the plasma responses to both lutein (14 (95 % CI 3·7, 25) %) and folate (10 (95 % CI 2·2, 18) %), whereas it did not affect the response to β-carotene. We conclude that the bioavailabilities of β-carotene and lutein vary substantially among different vegetables and that the bioavailabilities of lutein and folate from spinach can be improved by disruption of the vegetable matrix.

(Received May 18 1998)

(Revised December 17 1998)

(Accepted April 28 1999)

Correspondence:

c1 *Corresponding author: Dr Karin van het Hof, fax +31 10 46 05 993, email Karin-van-het.hof@unilever.com