It all started with a 16-hour flight to Australia. Two researchers—one from Utah, the other from Connecticut—both headed off to the International Conference on Carotenoids, those all-important compounds (beta-carotene, lutein, lycopene) that give vegetables their color. For over a decade, Werner Gellermen, a physicist at the University of Utah, had been working to find a way to measure these pigments in people’s retinas using laser light. In 2001, he patented the technology and began licensing hundreds of machines to companies selling nutraceuticals, food products with supposed health benefits. "You can test the efficacy of all of these supplements by measuring their effect on the human body," he says. "You don’t have to believe what the company is touting around. It’s kind of a 'truth check.’"
Susan T. Mayne, an epidemiologist at Yale University, had another problem. Ask people if they ate their vegetables and they’ll say, "Why yes, of course I do." Self-reported nutritional data, while inexpensive and easy to gather, often comes with reporting biases. Since carotenoids are neither found in hair nor fingernails, researchers looking for these nutrient biomarkers use an invasive "dermal posterior hip biopsy"—punching out a three millimeter hole in your skin. This is both costly and painful.
Then, in 1999, the two sat down on the plane to Australia. By the end of the 16-hour flight, they had come up a plan to solve Mayne’s problem using a smaller and more portable laser than in Gellermen’s retina scanner. And instead of scanning the retina, it would scan the largest organ in our body. "We chanced on the detection of these compounds in the skin," Gellermann says. "We got lucky because the concentration in the skin is a factor of 100 lower than in the retina."
The portable veggie-meter works on the principal of Raman spectroscopy, which was discovered in 1930. A fiber-optic probe is held to a person’s palm or inner forearm for about 30 seconds, and a blue laser beam shines onto the skin. To the naked eye, carotenoids look yellow; they’re absorbing blue wavelength light. By measuring the weak green light reflected off the skin, the device can find how many carotenoids are present. "The more your skin has, the brighter the green light." (The technique has also shown promise in detecting salmonella and the nutritional composition of breakfast cereal). Mayne and Gellerman published a study in 2010 in The American Journal of Clinical Nutrition comparing the method with biopsies; the invasive method versus the laser light. Both came back with similar results. The laser appeared to work.
While the method requires further testing, currently underway at the U.S. Department of Agriculture labs, a "veggie-meter" might offer better data for dietary interventions: How does diet tie in with the risk of developing cancer? Do people receiving federally financed supplemental nutrition eat more vegetables when they live near farmers’ market that double the value of food stamps? Or perhaps if you’re just feeling competitive, it might even be useful at the neighborhood gym. "We measure ourselves all the time," Gellermann says. "It is a lot of fun when you have like ten people in the room. You can find who is the lowest and say, ‘Well, no wonder, you are a meat eater. You don’t eat any vegetables.’" The laser doesn’t lie.