But consumption of tomato-based products, including supplements that contain lycopene in combination with other carotenoids and phytochemicals, such as LycoRed's Lyc-O-Mato, do give a "significant health benefit" said the reviewers.
The review may have implications considering the recent FDA ruling in the US concerning health claims for tomatoes and lycopene.
After much waiting, the FDA finally ruled in November of last year that only tomato and tomato sauce products may make heavily qualified health claims on their packaging about their ability to reduce the risk of prostate, gastric, ovarian and pancreatic cancers - and these are couched in very negative terms, "unlikely", "highly uncertain", and "highly unlikely".
The approval fell way short of the petitioner's (American Longevity) hopes. It had asked the agency to consider evidence that the risk reduction could be attributed to lycopene. This would have meant that tomato-based products and dietary supplements containing lycopene, where other tomato phytonutrients are not necessarily present, could also make the claims.
Tomatoes are a valuable source of nutrients, including beta-carotene, vitamins C and E, and lycopene, a potent antioxidant that gives the fruit its characteristic red colour.
It is well known that lycopene is more bioavailable when the tomatoes are processed and/or cooked, but optimal conditions for lycopene bioavailability are not established.
The new review, by Arpita Basu, formerly of UC Davis Health System and now at Oklahoma State University, and Victorine Imrhan from Texas Woman's University, considered results from clinical trials of tomato and tomato-based products on raising levels of antioxidants in the blood, and in protecting against cancer.
A number of clinical trials, dating from 1998 to 2006, were reviewed, each using different types of lycopene supplementation, including spaghetti sauce, tomato juice, tomato puree, Lyc-O-Mato capsules, and tomato paste. Biomarkers to test for any effects of the supplementation included DNA damage, levels of LDL-cholesterol oxidation, and levels of PSA (a marker of prostate cancer).
Basu and Imrhan found that supplementation provided bioavailable sources of lycopene, which increase lycopene concentrations in the blood. They also concluded that these types of supplementation lowered levels of biomarkers of oxidative stress and carcinogenesis in healthy people, type-2 diabetics, and prostate cancer patients.
It was also found that dietary fats like olive oil boosted the bioavailability.
In terms of pure lycopene alone, the reviewers point out that many in vitro studies have shown "convincing antioxidant and anticarcinogenic effects" for the carotenoid.
However, in vivo data on the effects of pure lycopene supplementation is lacking, they said, and thus its role per se remains to be investigated.
"It can be concluded that moderate amounts of whole food-based supplementation (two to four servings) of tomato soup, tomato puree, tomato paste, tomato juice, or other tomato beverages, consumed with dietary fats, such as olive oil or avocados, leads to increases in plasma carotenoids, particularly lycopene," wrote the researchers in the European Journal of Clinical Nutrition (doi: 10.1038/sj.ejcn.1602510).
It remains to be seen if such conclusions will prompt new petitions to the FDA, but the statements by Basu and Imrhan lend support to the stance that supplements made from tomato extracts, such as Lyc-O-Mato, should also qualify for approval.
Lyc-O-Mato not only contains lycopene in concentrations from five to 15 per cent, but also contains other natural tomato phytonutrients, such as tocopherols, phytoene, beta-carotene, and phytosterols. It is not eligible to use health claims according to the FDA approval.
A recent risk assessment by the US-based trade association, the Council for Responsible Nutrition (CRN), concluded that sufficient data from 16 randomised clinical trials to establish an upper safe limit for the carotenoid of 75 mg/d. (Regulatory Toxicology and Pharmacology, doi: 10.1016/j.yrtph.2006.05.007).