Watermelon juice increases plasma concentrations of lycopene and beta-carotene - Dietary Intake

Nutrition Research Newsletter, May, 2003

Watermelon is one of few foods rich in lycopene, a nonprovitamin A carotenoid that has up to twice the antioxidant capacity of beta-carotene in vitro. Data from epidemiological studies suggest lycopene may have protective effects against certain types of cancers and cardiovascular disease.

Previous investigations of lycopene bioavailability have focused on tomato products, which represent 80% of lycopene intake in the US diet. Other natural food sources of lycopene include guava, pink grapefruit, apricots, persimmons, and red-fleshed papaya, although the contribution of these foods to dietary lycopene is limited. The mean lycopene concentration of watermelon (4868 micrograms/100 g) is about 40% higher than the year-round mean for raw tomato (3025 micrograms/100 g), and watermelon ranks 5th among the major contributors of lycopene in the US diet. However, the bioavailability of lycopene from watermelon has not been evaluated.

The primary objective of this study was to assess the bioavailability of lycopene from watermelon juice using tomato juice as a comparative lycopene-rich food. As secondary objectives, the researchers sought to determine whether a measurable dose-response in plasma lycopene occurs when the amount of watermelon juice consumed is doubled and to compare the plasma lycopene response to tomato and watermelon juices providing a similar amount of lycopene. Plasma responses from other carotenoids present in watermelon and tomato, including beta-carotene, phytoene and phytofluene, were also examined.

Over 19 weeks, 22 healthy subjects (mean BMI 27 [ or -] 4 kg/[m.sup.2] and mean age 51 [ or -] 10 y) consumed three of four possible treatments, according to a repeated-measures crossover design. Treatments were as follows: 1) C-0, control or base diet only; 2) W-20, base diet plus 20.1 mg/d lycopene and 2.5 mg/d beta-carotene from watermelon: 3) W-40, base diet plus 40.2 mg/d lycopene and 5.0 mg/d beta-carotene from watermelon; and 4) T-20, base diet plus 18.4 mg/d lycopene and 0.6 mg/d beta-carotene from tomato juice. Subjects consumed W-20 and C-0 in separate treatment periods, plus either T-20 or W-40 in a third treatment period. Four-week washout periods, during which subjects limited consumption of lycopene-containing foods, were completed between treatment periods 1 and 2, and 2 and 3 to minimize carryover effects on plasma lycopene. A two-week washout period was completed before treatment period 1 to allow plasma lycopene to reach stable baseline levels before treatment. Subjects consumed their own foods, but kept written records of fruit, vegetable, and beverage intake during the washout periods.

Fresh-frozen watermelon juice produced a significant increase in plasma lycopene, comparable to the increase observed with a similar amount of lycopene from canned tomato juice. Within one to two weeks, consumption of ~20 mg/d lycopene from either watermelon or tomato juice resulted in a 100% to 200% increase in plasma lycopene in human subjects. Heat treatment was thus not required for lycopene absorption from fresh-frozen watermelon juice.

Although there has been some doubt about the bioavailability of lycopene from tomato juice, the researchers demonstrated an increase in plasma lycopene from 428 nmol/L to 960 nmol/L over three weeks using 18.4 mg/d lycopene from 240 g (1 cup/d) of tomato juice. After W-20, W-40, and T-20 treatments, plasma lycopene concentrations were significantly elevated above control by week 1, reaching a maximum at week 2 and a plateau between week 2 and week 3. Gender effects were significant for both beta-carotene and lycopene, whereas BMI was not a significant covariate for either beta-carotene or lycopene, and age was a significant covariate for beta-carotene only.

(1) LYC, lycopene. (2) Watermelon (W-20, W-40) and tomato (T-20) juice treatments were consumed in addition to base diet (C-0). (3) Fiber content of watermelon juice was below detection limit (0.1 g/100 g total dietary fiber) of AOAC Method 991.43 (27). (4) Carotenoid and fiber content of 10,040 kJ base diet (C-0), which provided 1.3 mg LYC/wk or < 0.2 mg LYC/d. (5) Values for phytoene and phytofluene in base diet are not available (n/a).

In healthy human subjects, in the presence of ample fat, lycopene was bioavailable from watermelon juice and produced an increase in plasma lycopene similar to that of tomato juice. This is the first report to demonstrate that lycopene is bioavailable from a watermelon product. The researchers used watermelon in juice form to provide a consistent product across the months of controlled feeding. This would not have been possible with the whole fruit because of the large interindividual variability in lycopene content of watermelons. Although use of the juice limits the extrapolation of the data to whole watermelon, the juice contained pulp from fresh watermelon and was not heat processed, factors supporting the concept that lycopene is bioavailable from whole watermelon.

In conclusion, the researchers of the current study evaluated lycopene bioavailability from two food sources, with no additional heat treatment, and found that lycopene was bioavailable from both fresh-frozen watermelon and canned tomato juices. Plasma concentrations of lycopene were significantly and similarly elevated from 18 to 20 mg lycopene per day from fresh-frozen watermelon juice or canned tomato juice. Heat treatment was not necessary for lycopene absorption from watermelon juice. There was no apparent dose-response effect for plasma lycopene when the amount of watermelon juice consumed was doubled. Watermelon may serve as a bioavailable source of lycopene in the diet.