Epidemiological and cohort studies have shown that the consumption of tomato products lowers the risk of degenerative diseases. The health benefits of tomatoes are attributed to lycopene, a strong antioxidant with antiproliferative actions. Lycopene has a structure similar to that of the well-known antioxidant beta-carotene, but its antioxidant activity is much stronger. Tsen and co-workers were able to explain why lycopene is more potent than beta-carotene in neutralizing singlet oxygen, a strong free radical. By using an ultrafast Raman spectrometer they demonstrated that excitation energy of singlet oxygen is transferred to the first excited electronic state of beta carotene and directly to the ground excited vibronic state of lycopene. The antioxidant capacity of lycopene offers protection against gamma-radiation induced damage to cells . A study lead by Srinivasan even concluded that lycopene could be developed as effective radioprotector during radiotherapy of cancer patients. This in-vitro study was carried out on rat hepatocytes, which were pre-treated with lycopene and exposed to different levels of gamma-radiation. The pre-treatment resulted in a significant reduction of DNA damage and lipid peroxidation (as measured by thiobarbituric acid reactive substances).
Other components may also play a role in the protective effects of tomatoes. A study by Gitenay et al. showed that tomatoes, even yellow varieties without lycopene, showed a stronger antioxidant effect in rats. Rats with mild oxidative stress, caused by low vitamin E level, were fed with placebo, yellow tomato extract, red tomato extract or lycopene. All diets had no effect on plasma cholesterol but only the red tomato diet reduced triglycerides. Rats fed with yellow or red tomato extract showed lower levels of thiobarbituric reactive species in the heart than those fed with placebo or lycopene. This led the researchers to conclude that tomatoes, containing lycopene or not, have a higher potential than lycopene alone to attenuate oxidative stress parameters in a mild oxidative stress context .
Other studies have also come to the conclusion that not only lycopene but also other components. A study by Bose and co-workers came to the conclusion that the consumption of tomatoes may have considerable natural therapeutic potential as an antioxidant but not as hypolipidemic agent in hypertension. They tested the effect of tomato consumption on group of hypertensive individuals. Compared to normal individuals, hypertensive individuals show a low antioxidant enzyme activity, high lipid peroxidation rate and high serum levels of cholesterol and triglycerides. There was no significant effect on lipid profile but tomato consumption significantly decreased lipid peroxidation and increased antioxidant enzyme activity . Consumption of tomato juice during 2 weeks by human volunteers showed that lycopene reduced plasma cholesterol and C-reactive protein . Addition of ascorbic acid showed an increased effect. Only when the tomato juice was enriched with extra ascorbic acid, the antioxidant capacity in urine was slightly increased and levels of thiobarbituric acid reactive substances (index of lipid peroxidation and oxidative stress) in urine and serum were slightly decreased. Other biomarkers of oxidative stress and inflammation were not or only slightly changed. This led Jacob B and his co-workers to conclude: "Any beneficial effects of tomato consumption for human health cannot be attributed only to lycopene and, as the additional supplementation with ascorbic acid indicates, a variety of antioxidants might be needed to optimize protection against chronic diseases".
The antioxidant capacity of lycopene was also demonstrated by Bansal and co-workers in an ischemia and reperfusion experiment . In untreated rats the ischemia-reperfusion injury resulted in significant myocardial damage, reduced blood circulation, reduced anti-oxidant status and increased lipid peroxidation. Treatment of the rats with lycopene reversed these unfavorable effects and restored the functionality of the heart. Lycopene probably acted by suppressing the oxidative stress. High blood levels of iron can cause oxidation and may be carcinogenic. A Brazilian study led by Matos demonstrated that rats treated with a high level of iron (ferric nitrilotriacetate) significant increased DNA damage and malondialdehyde (indicator of lipid oxidation) level in the prostate. The pre-treatment of the rats reversed these effects: lipid and DNA damage was almost completely prevented .
A study on adult asthma patients showed the intake of tomato juice or a tomato extract (both corresponding to a daily intake of 45 mg lycopene) inverted the unfavorable effect of a low anti-oxidant diet on asthma and airway inflammation. Intake of tomato juice or lycopene extract resulted in a reduced influx of white blood cells in the airway. Treatment with the lycopene extract also reduced the activity of neutrophil elastase, a role in degenerative and inflammatory diseases .
 Gitenay D, Lyan B, Rambeau M, Mazur A, Rock E. " Comparison of lycopene and tomato effects on biomarkers of oxidative stress in vitamin E deficient rats." Eur J Nutr. 2007 Dec;46(8):468-75.
 Bose KS, Agrawal BK. " Effect of lycopene from tomatoes (cooked) on plasma antioxidant enzymes, lipid peroxidation rate and lipid profile in grade-I hypertension." Ann Nutr Metab. 2007;51(5):477-81.
 Jacob K, Periago MJ, Böhm V, Berruezo GR. "Influence of lycopene and vitamin C from tomato juice on biomarkers of oxidative stress and inflammation." Br J Nutr. 2008 Jan;99(1):137-46.
 Rencuzogullari N, Erdogan S. " Oral administration of lycopene reverses cadmium-suppressed body weight loss and lipid peroxidation in rats." Biol Trace Elem Res. 2007 Aug;118(2):175-83.
 Atessahin A, Ceribasi AO, Yilmaz S. "Lycopene, a carotenoid, attenuates cyclosporine-induced renal dysfunction and oxidative stress in rats." Basic Clin Pharmacol Toxicol. 2007 Jun;100(6):372-6.
 Tsen KT, Tsen SW, Kiang JG. " Lycopene is more potent than beta carotene in the neutralization of singlet oxygen: role of energy transfer probed by ultrafast Raman spectroscopy." J Biomed Opt. 2006 Nov-Dec;11(6):064025.
 Srinivasan M, Sudheer AR, Pillai KR, Kumar PR, Sudhakaran PR, Menon VP. " Lycopene as a natural protector against gamma-radiation induced DNA damage, lipid peroxidation and antioxidant status in primary culture of isolated rat hepatocytes in vitro. " Biochim Biophys Acta. 2007 Apr;1770(4):659-65.
 Bansal P, Gupta SK, Ojha SK, Nandave M, Mittal R, Kumari S, Arya DS. " Cardioprotective effect of lycopene in the experimental model of myocardial ischemia-reperfusion injury." Mol Cell Biochem. 2006 Sep;289(1-2):1-9.
 Matos HR, Marques SA, Gomes OF, Silva AA, Heimann JC, Di Mascio P, Medeiros MH. "Lycopene and beta-carotene protect in vivo iron-induced oxidative stress damage in rat prostate." Braz J Med Biol Res. 2006 Feb;39(2):203-10. Epub 2006 Feb 2.
 Wood LG, Garg ML, Powell H, Gibson PG. " Lycopene-rich treatments modify noneosinophilic airway inflammation in asthma: Proof of concept." Free Radic Res. 2008 Jan;42(1):94-102.