The Color System of Antioxidants

The different types of antioxidants can, for the most part, be grouped by color. For example, the antioxidants found in red tomatoes are identical to those found in red watermelon or pink grapefruit. Although the system is by no means perfect, organizing phytochemicals by color is an easy way to help you differentiate between the different types of antioxidants and learn how to get a variety of phytochemicals and antioxidants into your diet.

The red group, including tomatoes, pink grapefruit, and watermelon, contain lycopene, one of the most well-studied antioxidants in the fight against prostate cancer. Population-based studies that were conducted when prostate cancer was diagnosed at more advanced stages clearly demonstrated that increased blood levels of lycopene and increased intake of lycopene-containing foods were associated with a reduced risk of aggressive prostate cancer. In recent years, as the population of prostate cancer patients has shifted to the identification of cancers at earlier stages, and as the population of patients has changed, some of these associations can no longer be demonstrated.

There are several short-term studies in which tomato paste or lycopene supplements were given to men prior to prostatectomy. Lycopene was identified in the prostate tissue after surgery and there were changes in prostate cells suggesting benefit. Multiple animal studies have also demonstrated the ability of lycopene to reduce tumor growth as well. It is also clear from multiple studies that the benefits of lycopene are more readily available when absorbed from cooked tomato products and juices than from whole tomatoes. In fact, more than 80% of the lycopene in the American diet comes from cooked tomato-based products such as pasta sauce, tomato soup, tomato juice, and ketchup.

Ultimately, studies focused on the ability of lycopene to prevent the initiation and progression of prostate cancer have not yet established definitively the benefits of increasing the intake of lycopene-containing foods or supplements. More research is needed to clarify the potential benefit of this nutritional component.

Importantly, some animal studies have shown minimal or no benefit to lycopene alone for slowing prostate cancer growth, while whole tomato extracts have been shown to slow tumor growth. Thus, the benefits to the red group are likely due to more than just lycopene, and simply taking a lycopene supplement will not confer the same benefit as eating whole fruits and vegetables. Again, this is a simple reminder that there are no shortcuts to a healthy diet and regular exercise.

The red/purple group, including pomegranates, grapes, plums, and assorted berries, all contain anthocyanins, which accounts for the color of the group. However, different berries in this group have unique properties. For example, pomegranates have ellagitannins, which inhibit inflammation and may have benefits for heart health, cancer prevention, and dementia, while cranberries have proanthocyanidins, which target a bacteria common in urinary tract infections. The full benefits of blackberries, strawberries, and raspberries are still being studied, but they all have antioxidant power and work together with the other red/purple berries.

The orange group, including carrots, mangoes, apricots, cantaloupes, pumpkin, and sweet potatoes, contain alpha and beta carotenes. Beta-carotene, the more well-studied of the two, is converted by the body into vitamin A, which is important for vision, and works together with the red, green, and yellow/green antioxidants. Note that carrots provide about half the alpha and beta carotene in the average American diet, with significant contributions from tomato-based products.

The orange/yellow group, including oranges, peaches, papaya, and nectarines, contain betacryptoxanthin, a minor carotenoid that accounts for only a minute amount of the daily intake of all carotenoids by the average American. About 87% of cryptoxanthin comes from orange juice, oranges, and tangerines. However, one must be cautious about relying on processed juices as some of the nutrients are removed during production and high amounts of sugars are often added.

The yellow/green group, including spinach, collard, yellow corn, green peas, avocado, and honeydew melon, contain lutein and zeaxanthin. These carotenoids concentrate in the eye and contribute to eye health. Lower intakes have been associated with cataracts and age-related macular degeneration, the primary preventable cause of blindness in America.

The green group, including broccoli, Brussels sprouts, cabbage, bok choy, and kale, contain sulforaphane, isothiocyanates, and indoles. These compounds stimulate genes in the liver to produce enzymes that break down carcinogens, including those that are produced when overcooking and/or charbroiling meats.

The white/green group, including garlic, onions, asparagus, leeks, shallots, and chives, contain allyl sulfides, which activate an antioxidant response in cells.

Plant foods that don’t fit into the color system can also have unique benefits. For example, celery has salicylic acid, which is closely related to the active ingredient in aspirin and has been used for centuries to relieve headaches. Mushrooms are a complex group of plant foods with possible  effects on the immune system at the level of the intestines.

Also, keep in mind that because the color of the fruit or vegetable is tied to its chemical properties, foods with deeper, richer colors are typically more nutritious. Compare, for example, a regular store-bought tomato with one bought from a local farm. To be able to ship a firm tomato by truck, the tomato is picked while it is still green and is rapidly ripened by being blasted with ethylene gas, a substance normally produced by the plant as a signal to ripen. While ripening, the family of lycopene compounds accumulates, especially in response to heat and light. However, once ripening stops, the accumulation of lycopene stops. Because the ripening process is stilted, the color of the typical store-bought tomato is often somewhat washed out. By contrast, the tomato that ripens naturally on the vine at the local farm is typically deeper in color and richer in taste — and thus more nutritious.

Incorporating a variety of both colorful and colorless phytochemicals in fruits and vegetables can help to maximize intake of key chemical elements required to maintain healthy tissues and reduce the risk of disease.