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Trash-Collecting Researchers Find Dietary Patterns in Discarded Hair Clippings



Poorer people in the U.S. tend to have less access to nutritious foods than the wealthy. Measuring the dimensions of the problem can be tricky because diet research often depends on inaccurate surveys and requires contacting hundreds, if not thousands, of people

A study published on August 3 in the Proceedings of the National Academy of Sciences USA reports on an unorthodox approach to more easily assess how meat and plant consumption varies among communities of differing socioeconomic status—and, potentially, how dietary patterns change over time.

Specifically, to look at how people consume their protein, the authors collected discarded hair from barbershops and hair salons. Different foods have different ratios of isotopes, or variants of a particular element, that end up as parts of amino acids–—protein building blocks in our body, including our hair.

The researchers analyzed carbon and nitrogen isotope ratios in the samples to determine the form of dietary protein people consumed and compared their findings with U.S. Census data on socioeconomic status. In North America, meat has very different carbon and nitrogen ratios than vegetables. And carbon ratios further indicate whether consumed meat came from corn- or grass-fed animals.The study found that in areas with lower socioeconomic status, corn-fed animal proteins, which are often found in fast food, were more common than plant proteins in the average diet.

Across all populations, animal proteins comprised more than 55 percent of the diets analyzed. Yet in lower-income populations, that figure climbed as high as 75 percent. The affluence of each community was determined by looking at cost of living, mean household income and the average price of a haircut in a given zip code.

Isotopes have long been examined to measure human and natural activity. Besides looking at diet, study co-author James Ehleringer, a  biologist and geophysics researcher at the University of Utah, has used isotope ratios to explore questions about counterfeit labeling in coffee beans, lawn management and unidentified remains in forensic investigations since the 1990s.

Some of the data in the new study go back to 2008, when Ehleringer, published a paper showing that hydrogen and oxygen isotope ratios in people’s hair could be mapped to where they drank water in the contiguous U.S. Last year he decided to use some of the data from that earlier study—along with newly gathered research—to look at diet patterns that could be deduced by examining hair.

Ehleringer and University of Utah professor Thure Cerling put together a low-budget team that consisted of academic colleagues and even some family members. Ehleringer’s wife, Edna, along with Cerling’s college-age children, Claire and Dylan, were eager to take a road trip. The team randomly selected barbershops and hair salons within a particular zip code. As was the case for the 2008 study, it got approval from business owners to take hair from their garbage. The researchers sorted what they gathered from each shop into clusters that they thought might be tied to a particular individual. But no attempt was made to identify a salon patron—nor did Ehleringer and his colleagues use the hair clippings to pinpoint a person’s age, gender, travel or health status.

The team ultimately ended up with samples from 65 cities in the central and western U.S. It also took them from 29 zip codes in Utah’s Salt Lake Valley to get an intensive look an urban area. Hair isotope ratios varied within a somewhat narrow range. But it was still possible to correlate them with living costs in specific zip codes, enabling the finding that lower-income areas consumed more meat. (Earlier research had established isotope values that could be used to identify diets ranging from vegan to meat-heavy.)

One surprise came when the investigators realized that the levels of carbon isotopes in samples from the Salt Lake Valley could be linked to prices for a haircut, depending on a zip code’s socioeconomic level. They also calculated trends in body mass index for some zip codes and found that isotope ratios were linked to higher obesity rates in lower-income areas.

While he is not a nutrition expert, Ehleringer points to research tying meat consumption to negative health consequences. Using discards from barbershops and hair salons, he hopes, will provide experts in the field with an inexpensive means of studying dietary patterns on a large scale. “Our easy-to-use ‘stable isotopes in hair’ approach provides a means for community assessments that are free of the more typical survey-based approaches,” Ehleringer says. “Our hope is that the health community will consider this kind of assessment in [its] efforts to obtain large-scale [dietary] patterns. The analysis cost is less than $10 per person, making it affordable.”

Some recent data suggest that red meat and the saturated fat that comes with it may not be as harmful as previously thought. But plenty of studies link animal-based foods—particularly processed meats such as hot dogs, bacon, bologna and salami—with a variety of health risks.

Contributing to the problem, Ehleringer and many health experts contend, is the question of access. Massive industrial feedlots, or “concentrated animal feeding operations,” have made cheap protein much more available in the U.S.—a trend that differs from that of other countries. “In Brazil, it is the more economically advantaged people that have greater access to meats,” Ehleringer points out. (He was a co-author of a study this year that examined isotope ratios in fingernail clippings of Brazilians to determine what was in their diet.)

Harvard University nutrition and epidemiology professor Qi Sun says this study is an important contribution to the field of socioeconomic determinants of diet quality. Research such as Ehleringer’s, he hopes, should encourage the U.S. government to adopt strategies to improve the affordability and availability of healthy foods in poorer populations. “This study may help the policy makers allocate resources to the socioeconomically disadvantaged communities for not only information dissemination but also assistance in eventually reducing their animal intake,” Sun says.

For the first time in decades, global meat production is on the decline—as is meat consumption in the U.S. But Sun asserts that too much red meat is still being consumed. He is heartened, though, by the food industry’s exploration of plant-based meat alternatives, including the Impossible Burger and Beyond Burger. Red meats such as beef, lamb and pork, as well as processed meats, Sun says, should have little or no role in a healthy diet, because obesity is so widespread and is associated with diabetes, heart disease and early mortality.

Cerling says that the researchers’ intention was to use the tools that they had to help address poor nutrition in the U.S. “Better access to information is needed,” he says. “And our hope is that our study provides additional information so that policy makers can make an informed judgment.”



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