In the present study, a tomato variety rich in phytochemicals, with growth characteristics suitable for Ohio agriculture, was combined with soy germ to result in a final product with a well-characterized dose of phytochemicals. Tomato profiles can be influenced by both horticultural conditions such as cultivars, soil, growth conditions, and further by food processing techniques, selectively enhancing phytochemical rich fractions or altering their chemistry to favor absorption and bioactivity (37
). Thus, from a horticultural, food science, and consumer perspective, tomatoes provided an ideal platform for developing a product enriched with anticancer food components.
The initial human study showed that the soy-fortified tomato juice, consumed twice daily (total of 300 ml) for 8 wk, was easily incorporated into a daily diet, allowed excellent compliance, and was very well tolerated by healthy men and women without any documented adverse effects. In general, regulatory agencies consider the consumption of soy isoflavones (39
) and tomato carotenoids (40
) to be safe over a large range, with few, if any acute side effects. However, a careful documentation of compliance and toxicity is a prerequisite for proposing longer-term studies.
Carotenoids were readily absorbed from the soy-tomato juice. Lycopene was the major carotenoid in the soy-rich tomato juice and was detected in the plasma-TRL fraction within 2 h following a single-dose test meal, which is in agreement with earlier observations with other tomato products (10
). Soy-tomato juice provided higher plasma-TRL lycopene concentrations than tomato salsa with avocado (40 mg lycopene) (10
) but was comparable to lycopene capsules (38 mg) ingested with a complex meal (35
). It has been suggested that the efficiency of lycopene absorption declines with total dose but increases with concomitant fat intake (41
). Lycopene showed 2 absorption maxima, one in the immediate hours after the test meal consumption and another one following the subsequent lycopene-free lunch, possibly as lycopene from the first meal remained in the enterocytes until long-chain fatty acids from a subsequent meal enables lycopene packaging into chylomicrons and movement to the venous circulation via lymphatic flow through the thoracic duct.
During the course of the study, concentrations of lycopene and β
-carotene in plasma increased approximately 3-fold and 2-fold, respectively, at 4 and 8 wk compared to baseline. Even though baseline values (both prior and following washout) in the present study were comparable to other intervention studies using tomato juice, the resulting increase in plasma lycopene was somewhat higher than reported previously, typically being in the range of 0.5–0.8 μ
). In some (42
), but not all studies (32
), these results were attributable to lower lycopene intake. This indicates that the juice provided consistently elevated and relatively high plasma lycopene concentration such as those reported to be correlated with reduced risk of certain cancers (4
The detected presence of carotenoid cis-isomers in vivo, the factors that influence their formation and the biological relevance remain a source of debate. Although 5-cis lycopene was not detectable in the juice, this isomer was the predominant one in the baseline corrected TRL-AUC response. This indicates that conversion must have occurred at some step following ingestion and entry into the circulation. The finding that 41% of total lycopene was in the trans form in the baseline corrected TRL-AUC response following test meal ingestion but was only 18% of total lycopene in whole plasma during the later part of the study (Weeks 4 and 8), supports the hypothesis that lycopene is continuously isomerized in vivo to cis-isomers.
For the native isoflavones daidzein and genistein (or their glycosides), a similar absorption pattern following test meal consumption with 2 maxima was observed, perhaps due to enterohepatic recycling (45
), or absorption from the large intestine (46
). Alternatively, fat or other components provided by the second meal could have fostered absorption of isoflavones, as suggested earlier (47
). Contrary to earlier reports indicating highest plasma appearance for genistein (49
), we observed that daidzein and genistein were absorbed to a similar extent, while glycitein appearance in plasma was lower, being in line with previous reports (45
). However, urinary excretion showed a higher recovery of glycitein compared to genistein, also noted by others (45
). It is possible that genistein was more rapidly metabolized to undetected compounds such as p-ethylphenol.
Isoflavone concentrations in urine appeared to remain relatively constant at wk 4 and 8. We observed an excretion level which is approximately 2 times higher than typically reported for Asian populations consuming soy containing foods, i.e., ingesting around 20–100 mg isoflavones/d (17
). Thus, the soy-tomato juice product achieved excretion profiles similar to populations experiencing lower risks of specific cancers and may provide a convenient way to achieve a similar phytochemical exposure during long-term clinical trials.
The metabolism of soy isoflavones by humans and how it is modulated by genetics, dietary patterns, and host factors remains an active and complex area of investigation. We observed that 5 of the 18 subjects were equol producers after 4 wk of juice consumption, increasing to 7 subjects during 8 wk of consumption. This demonstrates that subjects do change their isoflavone metabolic status, also suggested in other studies (51
). As equol may exhibit relatively strong estrogen activity compared with other isoflavonoids (36
), it has been speculated that equol producers may have unique biological effects—some potentially beneficial (bone health in women), while others detrimental, such as the increased tumorigenesis and breast cancer formation (16
), albeit this is controversially discussed (53
). Additional work, such as more long-term studies in this area, is needed to judge on the potential health benefits vs. adverse effects.
Although the main goals of this initial study with soy-tomato juice were compliance, safety, and metabolism, we also assessed several biological responses. Following consumption of soy tomato juice, biological changes observed included increased HDL-C, decreased ratio of total-C/HDL-C and improved VLDL+LDL-C resistance to Cu2+
-mediated oxidation. The observed mean increase in plasma HDL-C (9%) in the present study after 8 wk of intervention was in a similar range to that reported in a meta-analysis summarizing soy feeding trials (14
). It was also found that LDL-C decreased to a greater extent in men than in women. It has been reported that the cholesterol reducing effect of soy would be more pronounced in subjects with hypercholesterolemia (14
). One possible explanation is that the slightly higher cholesterol concentrations in men at the onset of the study responded stronger to the intervention.
Both lycopene (9
) and isoflavones (47
) have reported antioxidant properties in chemical assays and some data suggests the potential to exhibit similar properties in vivo (55
). It thus remains speculative which compounds in the soy-fortified tomato juice were responsible for the improvements in the blood lipid profile and the antioxidant status as measured by the LDL+VLDL-C oxidation. Consumption of tomato products has been shown to reduce LDL-C oxidation ex-vivo (32
). Supplementing soy appeared to have a similar benefit, although isolated isoflavones typically failed to be effective (57
). It has been shown that incorporation of isoflavones into LDL-C particles is relatively modest (58
) in contrast to lycopene, a very hydrophobic compound (1
). In other studies, isolated soy isoflavones failed to exhibit beneficial effects on plasma cholesterol concentrations (14
). It has been suggested that both the presence of soy protein and isoflavones in soy products are required to be effective (14
). In our study, soy protein intake was only about 4 g/day, suggesting that other factors were responsible for the observed effects on blood lipids. However, the fact that isolated compounds often failed to be effective highlights the importance of consuming whole foods containing a diverse array of components rather than supplementing individual compounds alone (59
In conclusion, this study demonstrates that a newly developed functional food, a soy germ-fortified tomato juice, was palatable, convenient, safe to consume, and well tolerated with no observed adverse effects. Furthermore, we demonstrated that lycopene and isoflavones were readily absorbed, remained at relatively high levels in biological fluids similar to that found in epidemiologic studies associated with lower cancer risk, and significantly improved blood lipid and antioxidant status during an 8-wk feeding trial in healthy subjects. This novel approach demonstrates that tomato juice is an excellent vehicle for the development of defined food products containing active phytochemicals. Future studies using new food products to deliver defined amounts and patterns of bioactive phytochemicals for long-term clinical trials targeting specific cancers are warranted.