Carotenoids are just about everywhere you look, at least in the natural world. These chemicals produce red, yellow, orange, and sometimes purple colors in plants and microorganisms, which use them to protect themselves against damaging sun rays, aid in photosynthesis, and stabilize cell membranes.
In animals (including humans), some carotenoids help cells communicate, facilitate cell growth, and protect the body from ultraviolet radiation and cancer. In the commercial realm, we use carotenoids to color foods, pharmaceuticals, and cosmetics.
Carotenoids include carotenes, lutein, and lycopene. The body can convert some carotenes, most notably beta-carotene, into vitamin A, a reaction that occurs either in the liver or the intestines. Vitamin A is vital for good vision, healthy skin, bone growth, and other body functions.
Carotenoids, including lycopene, can only be absorbed properly when eaten with some form of fat, since fat dissolves them and carries them through the body. Additionally, foods that contain carotenoids may need to be cooked, pureed, or finely chopped. This is especially true when the carotenoid is lycopene, which is found in calendula (Calendula officinalis), watermelon, tomato, guava, red grapefruit, bitter melon (Momordica charantia), carrot, rose hips, and apricot.
The Pros of Pizza
Some studies suggest that lycopene protects against coronary artery disease and colon, breast and prostate cancer. In fact, researchers have shown that lycopene accumulates in the prostate gland. A statistical study, spanning six years and published in 1995, focused on the diets of nearly 50,000 American men. The data show a relationship between lycopene-rich foods and a lower risk of prostate cancer. Of forty-six foods, only four showed a significant connection to lower prostate cancer risk: tomato sauce, tomatoes, pizza with tomato sauce, and strawberries. All of the tomato products are primary sources of lycopene (the strawberries are not). The study recommends increased vegetable and fruit consumption, especially of tomato-based products that have been cooked and concentrated into paste or sauce.
Studies such as this one only highlight statistical associations; they don’t prove that something prevents or cures a disease. “Proving” requires that humans take part in controlled research studies and that these studies can be duplicated.
To date, controlled studies indicate that carotenoids work synergistically with one another and other phytochemicals. In other words, they perform better when they team up. Just how carotenoids work together is open to debate, however, and studies have produced varying results.
In a 1997 French pilot study, researchers gave smokers and nonsmokers a diet beefed up with beta-carotene (mostly from carrots), lycopene (from pear tomatoes), and lutein (from green beans, cabbage, and spinach).
Before the study, researchers observed that the smokers’ overall carotenoid levels were lower than those of the nonsmokers. After two weeks on the diet, carotenoid levels increased 23 percent in smokers but only 11 percent in nonsmokers. In addition, the resistance of LDL (low-density lipoprotein) cholesterol—the type that increases risk of heart attack—to oxidation increased 14 percent in smokers and 28 percent in nonsmokers, which showed that the high-carotenoid diet had a definite antioxidant effect.
While these results were promising in terms of how carotenoids might help smokers, they were complicated by individual carotenoids behaving in different ways. Blood levels of alpha- and beta-carotene increased in both groups, but lutein increased only in smokers. Lycopene did not increase in either group.
Comparing these results to the study of 50,000 men, it appears there may be a subtle relationship between lycopene and prostate cancer that has not yet emerged. Or, perhaps the association between lycopene-rich foods and reduced cancer risk is not due to lycopene at all, but some other factor.
These contradictions don’t mean that the statistical associations found between carotenoids and cancer are wrong, just that more research needs to be done to understand specifically how lycopene and other carotenoids work. The benefit of fruits and vegetables is definitely present, so the longer you eat a diet rich in them, and therefore carotenoids, the better off you will be.
Hininger, I., et al. “Effect of increased fruit and vegetable intake on the susceptibility of lipoprotein to oxidation in smokers.” European Journal of Clinical Nutrition 1997, 51:601–606.
Voelker, R. “Pass the Pizza.” Journal of the American Medical Association 1997, 278:1482.
C. Leigh Broadhurst holds a doctorate in geochemistry and is a nutrition consultant in Clovery, Maryland.
James Duke is a member of the Herbs for Health Editorial Advisory Board. His most recent book is The Green Pharmacy (Rodale, 1997).