Carotenoids are thought to contribute to the beneficial effects of increased vegetable consumption. Various dietary factors have an effect on the bioavailability of carotenoids. The type of food matrix in which carotenoids are located is a major factor. The bioavailability of beta-carotene from vegetables in particular has been shown to be low (14% from mixed vegetables) compared with that of purified beta-carotene added to a simple matrix (e.g., salad dressing), whereas for lutein, the difference is much smaller (relative bioavailability of 67% from mixed vegetables). Processing, such as mechanical homogenization or heat treatment, has the potential to enhance the bioavailability of carotenoids from vegetables (from 18% to a sixfold increase). The amount of dietary fat required to ensure carotenoid absorption seems low (approximately 3-5 g per meal), although it depends on the physicochemical characteristics of the carotenoids ingested. Unabsorbable, fat-soluble compounds reduce carotenoid absorption, and interaction among carotenoids may also result in a reduced carotenoid bioavailability. Research into the functional benefits of carotenoids should consider the fact that the bioavailability of beta-carotene in particular is one order of magnitude higher when provided as a pure compound added to foods than when it is present naturally in foods.

The relative validity of a 104-item food-frequency method to assess intakes of fats and cholesterol was tested against the dietary history of 191 men and women. Pearson correlation coefficients ranged from 0.38 for linoleic acid (% of energy) to 0.83 for energy intake, with 0.78 and 0.75 for the intakes of total fat and saturated fatty acids, respectively. Mean intakes were overestimated by the food-frequency questionnaire relative to the dietary history by 5% for energy and monounsaturated fatty acids (% of energy) and up to 30% for linoleic acid intake. Linoleic acid concentrations in erythrocytes and adipose tissue were used as biomarkers of intake. The correlation of the linoleic acid intake according to the food-frequency questionnaire with linoleic acid in erythrocytes and adipose tissue was 0.44 and 0.28, respectively, and the dietary history gave similar values. The food-frequency questionnaire gives results similar to those from the dietary history and is thus considered appropriate for classifying subjects according to their fat intake.

The relationship of skinfold thicknesses to body density and of skinfold thicknesses to densitometrically determined body fat was evaluated in a group of 378 boys and girls, aged 7-20 years. According to their maturation level, they were divided into a prepubertal, a pubertal and a post-pubertal group. In each maturation group boys were older, had higher body-weights and body heights, higher body densities, lower percentage body fat, higher waist: hips ratios and higher trunk: total skinfolds ratios than girls. Body density in each maturation level could be quite precisely predicted by skinfold thicknesses. In prepubertal and pubertal boys and girls but not in post-pubertal boys and girls, age was also an important predicting variable for body density. The assessment of percentage body fat from skinfold thicknesses had a prediction error of 3-5 %, which was highest in the prepubertal children. The prediction error is comparable to the prediction error of percentage body fat from skinfold thicknesses in adults, as reported in the literature. Only in post-pubertal boys and girls was the waist:hip ratio correlated with measures of body fatness. Moreover, only in the post-pubertal boys and in the pubertal and post-pubertal girls was the waist: hips ratio correlated with another measure of body fat distribution, the trunk :total skinfold ratio. The relative amount of internal body fat was found to be higher in the younger maturation groups. It is concluded that at younger ages the waist: hips ratio is a poor indicator of body fat distribution.

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The objectives of this study were to quantify the effectiveness of dietary retinol sources, orange fruit, and dark-green, leafy vegetables in improving vitamin A status, and to test whether orange fruit is a better source of vitamin A and carotenoids than are leafy vegetables. Anemic schoolchildren aged 7-11 y (n = 238) in West Java, Indonesia, were randomly allocated to 1 of 4 groups to consume 2 complete meals/d, 6 d/wk, for 9 wk: 1) 556 retinol equivalents (RE)/d from retinol-rich food (n = 48); 2) 509 RE/d from fruit (n = 49); 3) 684 RE/d from dark-green, leafy vegetables and carrots (n = 45); and 4) 44 RE/d from low-retinol, low-carotene food (n = 46). Mean changes in serum retinol concentrations of the retinol-rich, fruit, vegetable, and low-retinol, low-carotene groups were 0.23 (95% CI: 0.18, 0.28), 0.12 (0.06, 0.18), 0.07 (0.03,0.11), and 0.00 (-0.06, 0.05) micromol/L, respectively. Mean changes in serum beta-carotene concentrations in the vegetable and fruit groups were 0.14 (0.12, 0.17) and 0.52 (0.43, 0.60) micromol/L, respectively. Until now, it has been assumed that 6 microg dietary beta-carotene is equivalent to 1 RE. On the basis of this study, however, the equivalent of 1 RE would be 12 microg beta-carotene (95% CI: 6 microg, 29 microg) for fruit and 26 microg beta-carotene (95% CI: 13 microg, 76 microg) for leafy vegetables and carrots. Thus, the apparent mean vitamin A activity of carotenoids in fruit and in leafy vegetables and carrots was 50% (95% CI: 21%, 100%) and 23% (95% CI: 8%, 46%) of that assumed, respectively. This has important implications for choosing strategies for controlling vitamin A deficiency. Research should be directed toward ways of improving bioavailability and bioconversion of dietary carotenoids, focusing on factors such as intestinal parasites, absorption inhibitors, and food matrixes.