We know that fruits and vegetables do us all kinds of good. But evidently they also give us a healthful glow — by tinting our skin yellow and red.
People's skin color changed in just six weeks when they increased their fruit and vegetable consumption, according to researchers in Scotland who compared eating habits to skin tone.
And while the cosmetics industry might have you believe that rouge is the ideal cheek color, this study found that another hue rated more healthful and attractive: yellow.
The students participating in the study who ate the most produce turned yellower than those who were subsisting on pizza and fries. The veggie eaters also looked ever so slightly rosier.
Fortunately, the change in skin tone was very slight; we're not talking blaze yellow here.
But in a second part of the experiment, people who were asked to rate digitally altered photographs could tell which photos had been tinted to make them slightly yellower. When asked to pick the people who looked healthier and more attractive, they picked the yellow ones.
"The take-home message is that improving your diet also improves your appearance within a relatively short time frame," Ross Whitehead, a graduate student in psychology at the University of St. Andrews who led the study, told The Salt by email.
It's long been known that eating a lot of carrots or other foods rich in carotenoids can turn skin orange. Apple founder Steve Jobs, who was known to eat only carrots for weeks on end, is said to sometimes have taken on a sunset hue.
But the Scottish study, published online in the journal PLoS One, found that the skin color change was more likely in people who ate one to three more servings of fruit and vegetables a day than they had at the beginning of the six weeks, on average. The 35 study participants chose what to eat, and reported it to the researchers. Some ate more fruits and vegetables over the course of the study, some less. Potatoes weren't counted as a vegetable.
The color shift in skin correlated to the wavelengths for two naturally occurring food pigments: beta-carotene, the pigment that makes carrots orange, and lycopene, which gives tomatoes their vibrant hues. We're not the only animals that can get color from carotenoids in plants; aphids do, too, as NPR's Joe Palca reports.
The scientists looked for increases in both red and yellow, but found the yellow shift to be much stronger. Whitehead says it may be harder to measure changes in rosiness because of fluctuations in the skin's blood flow.
When asked to pick the yellower face, people were able to distinguish a color difference equivalent to eating about two extra servings of fruit and vegetables a day. When they were asked to choose based on health and attractiveness, it was a bit harder. The yellowness had to be amped up to equal about three servings a day.
But since we're all supposed to be getting at least five servings of fruit and vegetables daily, eating three a day to be considered more healthy and good looking doesn't seem like too much of a stretch. Eating fruits and veggies is thought to lower the risk of heart disease, as NPR's Dick Knox reported.
This study isn't perfect. It's very small, with just 35 student participants. The students reported on their own eating habits, so that might not be accurate. And it used only Caucasian people, who are thick on the ground in Scotland.
But Whitehead says he's also tried the photograph test with images of people of color, and found that the people who were slightly yellower were considered healthier and more attractive there, too. He hasn't yet tested the correlation between diet and hue in non-Caucasians.
The study was partially funded by Unilever, which sells a wide variety of foods, including Lipton tea and Ragu spaghetti sauce. The company also sells personal care products, including the Dove and Vaseline lines. Given that, it's not hard to imagine why that company would be interested in this sort of research. But when asked, Whitehead said only: "Unilever is interested in the impact of diet, health and lifestyle on appearance — which is a strong motivator of behavior."