Skittles may have coined the catchphrase “Taste the Rainbow” to sell their colorful, sugary candies, but the adage has some truth for fruits and vegetables as well.
While processed food can contain a wide variety of artificial colorings, fruits and vegetables get their natural colors from phytochemicals, which are chemical compounds found in plants that help protect them against environmental threats. When consumed by humans, phytochemicals are associated with antioxidant properties and the production of different vitamins and minerals.
“Different colors are indicative of different nutrient content,” Dennis Miller, professor of food chemistry and nutrition at Cornell University, said.
Eating food from all across the color spectrum is good for your health, though it is a bit more complicated than following a rainbow to a nutritional pot of gold.
Phytochemicals and their colors
Phytochemicals can be grouped into a number of different categories, each with their own nutritional benefits. Though some phytochemicals display no colors at all, others create the colors of the spectrum of fruits and vegetables.
Carotenoids, for example, are a group of phytochemicals that produce vitamin A. Red fruits and vegetables are associated with the carotenoid lycopene, which research has shown can aid against the progression of certain kinds of cancer.
“Lycopene is a very powerful antioxidant,” Yanyan Li, associate professor of nutrition at Husson University, said. “We can find lycopene in tomato, which is probably the most famous source, and we can also find it in watermelon.”
Beta-carotene is another carotenoid that presents an orange or yellow color. As a precursor to the production of vitamin A, beta-carotene has been linked to promoting immune system health and aiding aging eyes.
“You can find a lot of beta-carotene in orange-colored fruit and vegetables, like sweet potatoes, cantaloupe and squash,” Li said. “We know it is very essential for our vision because it can be converted to retinol.”
Even among the same kind of fruit or vegetable, color seems to matter. Orange sweet potatoes, Miller said, have high amounts of beta-carotene, whereas white sweet potatoes do not. Red peppers contain almost 11 times as much beta-carotene as their green counterparts.
The phytochemical chlorophyll produces the green color of broccoli, spinach and kale. Darker green vegetables contain more chlorophyll and thus more magnesium, which is at the center of chlorophyll molecules and research has shown aids against chronic inflammation and warding off diabetes. Leafy green vegetables also contain the carotenoids lutein and zeaxanthin, which have been linked to promoting skin and eye health.
The uncertain science of phytochemicals
Even though some phytochemicals are associated with specific colors, it does not mean that the color of a food represents all its available phytochemicals.
“So far in total, we have identified more than a thousand phytochemicals from plants,” Li said. “Only a small portion of them actually have color.”
There are also no recognized recommended dietary intakes for phytochemicals.
“They do have health benefits, but they are not considered like fat and protein, which we need to make sure we have enough energy,” Li said. “Phytochemicals are kind of different. They are more like additional benefits.”
Li explained that the scientific research into phytochemicals is “relatively new,” and “most of the studies that have been done on phytochemicals have been done on cell cultures or animal models,” so it is difficult to determine their exact impacts on humans.
For this reason, Joe Schwarcz, director of the Office for Science and Society at McGill University, cautioned against using color as a simple catchall for nutrition.
“Nutrition is an unbelievably complex business,” he said. “The composition of our food is so complex. You have to be careful not to overstep the boundaries and imply that if you eat certain foods you can ward off some disease.”
Schwarcz said that when you study phytochemicals in isolation, they perform a variety of antioxidant functions, like neutralizing free radicals in a test tube. However, research has also shown a dark side to phytochemicals like carotenoids. Schwarcz cited a 2009 study that isolated beta-carotene and gave it to lung cancer patients. The study showed that the patients with the supplement did worse.
“When you take those antioxidants out of a fruit or vegetable and put it in a pill form, you don’t find the same effect,” Schwarcz said. He said that may be because in the plant, all of these phytochemicals are acting together synergistically producing an effect, but even that theory requires more research and does not account for the reactions that individuals may have to different phytochemicals.
“You can’t take something as complex as food, which contains thousands of compounds, put it in the most complex machine on earth, the human body, and get a simple answer,” Schwarcz said. “People will react differently.”
Why you should still eat the rainbow
Even though the ties between food’s color and its nutritional superpowers is tenuous and complex, most nutritionists agree that eating a variety of foods across the color spectrum is good for your health.
First of all, having a more diverse plant-based diet in general is also beneficial for your health.
“I don’t think anyone can argue against increasing the consumption of plant products even if the evidence is not ironclad,” Schwarcz said. “Populations that eat a lot of plant food are generally healthier than populations that don’t.”
Despite the inconclusive research, there is evidence to support the idea that phytochemicals do have healthful benefits. Because there is such a wide variety of phytochemicals, even ones that do not present colors, eating vegetables across the color spectrum will make sure you are getting the maximum nutritional benefits.
“Eating a variety of color can help make sure you get a variety of phytochemicals,” Li said. “Although many phytochemicals do not have color, if you eat a variety of food, you are going to get them anyway.”
“Because we don’t know which compound specifically is beneficial, the best bet is to eat across the spectrum,” Schwarcz added.