No abstract

The doubly labeled water method for measuring total energy expenditure is subject to error from natural variations in the background 2H and 18O in body water. There is disagreement as to whether the variations in background abundances of the two stable isotopes covary and what relative doses of 2H and 18O minimize the impact of variation on the precision of the method. We have performed two studies to investigate the amount and covariance of the background variations. These were a study of urine collected weekly from eight subjects who remained in the Madison, WI locale for 6 wk and frequent urine samples from 14 subjects during round-trip travel to a locale > or = 500 miles from Madison, WI. Background variation in excess of analytical error was detected in six of the eight nontravelers, and covariance was demonstrated in four subjects. Background variation was detected in all 14 travelers, and covariance was demonstrated in 11 subjects. The median slopes of the regression lines of delta2H vs. delta18O were 6 and 7, respectively. Modeling indicated that 2H and 18O doses yielding a 6:1 ratio of final enrichments should minimize this error introduced to the doubly labeled water method.

Objective: The purpose of this study was to determine if lycopene and b-carotene are bioavailable from lycopene red carrots and if lycopene absorption is affected by carrot fiber. Design: Two crossover studies in humans attempted to compare the relative bioavailability of lycopene and b-carotene from tomato paste to a genetically selected lycopene red carrot during chronic feeding. Each study contained three treatment groups. The vehicle of administration was muffins. Intervention and methods: Study 1 (n¼9) used white carrots (0 mg lycopene/day), red carrots (5 mg/day), and tomato paste (20 mg/day). Study 2 (n¼10) used red carrots (2.6 mg/day), tomato paste (5 mg/day), and tomato paste plus white carrots (5 mg/day). Each intervention lasted 11 days with a 10-day washout period between treatments. Serum lycopene and bcarotene were measured by HPLC. Results: Statistical analysis indicated a significant effect of muffin type in study 1 (Po0.001), and a significant treatment by sequence interaction in study 2 (P¼0.04). The response to increasing amounts of lycopene is linear at the levels fed in these studies (r¼0.94). The data suggest that maintenance of serum lycopene concentrations at 0.3 mmol/l occurs at about 2 mg/day of lycopene from mixed dietary sources and a serum plateau occurs at Z20 mg/day. Conclusions: These results show that lycopene and b-carotene are bioavailable from red carrots and lycopene absorption seems to be affected by carrot fiber. Making inferences from both studies, the lycopene in the red carrot is about 44% as bioavailable as that from tomato paste. Red carrots provide an alternative to tomato paste as a good dietary source of lycopene and also provide bioavailable b-carotene.

Beta-carotene is a predominant source of vitamin A in developing countries. Genetically selected "high carotene" carrots could have an impact on the vitamin A and antioxidant status of people if widely adopted. A 3 x 3 crossover study in humans (n = 10) evaluated the difference in uptake and clearance of alpha- and beta-carotene from carrots genetically selected and traditionally bred to have high, typical, or no carotene. Subjects were fed white (0 mg alpha- and beta-carotene/d), orange (1.8 mg alpha-carotene and 2.6 mg beta-carotene/d), or dark-orange (4 mg alpha-carotene and 7 mg beta-carotene/d) carrots in muffins for 11 d, with a 10-d washout phase between treatments. Serum carotenoid and retinol concentrations were measured by HPLC. C-reactive protein (CRP), an indicator of underlying inflammation or infection which may lower serum retinol, was measured at the beginning of each period. A significant treatment effect occurred for serum alpha- and beta-carotene concentrations (P < 0.001), and a trend towards a negative effect of subjects' BMI on concentrations (P= 0.08). A significant treatment by sequence interaction was observed (P = 0.038), which was attributable to a difference in serum alpha- and beta-carotene concentrations between carrot treatments in the first period. Serum retinol remained stable for the first 20 d of the intervention and then decreased (P = 0.02). CRP was not elevated in any subject. High carotene carrots provide more provitamin A carotenoids than the typical store-bought variety, without a change in flavor. The availability of high carotene carrots could readily increase consumption of beta-carotene and potentially impact the vitamin A status of those individuals who are deficient or at risk of depletion.