Lycopene the structure of the molecule was determined by 1931. In its natural, all-"trans" form, the molecule is long and straight, constrained by its system of 11 conjugated double bonds. Each extension in this conjugated system reduces the energy required for electrons to transition to higher energy states, allowing the molecule to absorb visible light of progressively longer wavelengths. Lycopene absorbs all but the longest wavelengths of visible light, so it appears red. Plants and photosynthetic bacteria naturally produce all-"trans" lycopene. When exposed to light or heat, lycopene can undergo isomerization to any of a number of "cis"-isomers, which have a
Lycopene from tomatoes has been tested in humans for cardiovascular diseases and prostate cancer, no effect on any disease was found. The US Food and Drug Administration (FDA), in rejecting manufacturers' requests in 2005 to allow "qualified labeling" for lycopene and the reduction of various cancer risks, provided a conclusion that remains in effect : "...no studies provided information about whether lycopene intake may reduce the risk of any of the specific forms of cancer. Based on the above, FDA concludes that there is no credible evidence supporting a relationship between lycopene consumption, either as a food ingredient, a component of