The tangled path the GI tract now leads through … hair. It turns out our durable and always-fashionable scalp adornment acts as a mirror of our eating habits, and can help determine whether patients are hiding some serious behaviors:
“Your body records your eating habits in the hair. So, we can use that to tell the nutritional health of an individual,” said lead researcher Kent Hatch, an assistant professor of integrative biology at BYU.
As hair grows, new proteins are added to the base of each strand, pushing the strand up and out of the hair follicle. These proteins are influenced by what you eat. And the nutritional state of each individual is affected by his or her eating patterns. So, each strand of hair is a chemical “diary” that is a record of day-by-day nutrition, the researchers said.
The new test analyzes two of these proteins, carbon and nitrogen. Based on the makeup of these proteins, the researchers said they’ve been able to diagnose eating disorders.
“By taking some hairs from an individual and analyzing it for carbon and nitrogen, we can tell with 80 percent accuracy whether someone has anorexia or bulimia,” Hatch said. “The test provides an objective way of discerning whether they have an eating disorder.”
More detail is present in the paper from Rapid Communications in Mass Spectrometry (references removed for clarity):
When the body is in an anabolic state, it incorporates dietary proteins into growing hair. Although the mechanism is unclear, it appears that 14N is excreted by the organism at a slightly higher rate than 15N. As a result, 15N concentrates in body tissues. Thus, as one moves up the food chain, 15N increases on average at 3% with each step or trophic level. Because of these trophic level effects, the 15N/14N ratios of herbivores (or vegetarians and vegans) are less than those of predators (or humans who eat more meat). Likewise, when the body becomes catabolic, the 15N/14N ratio of the individual’s tissues increases further due to something functionally similar to an increase in trophic level. As the individual loses weight, the individual’s body consumes its own energy and protein stores. The remaining proteins are 15N enriched and their amino acids are recycled. Some of these amino acids are incorporated into new hair growth, providing a signal of the change in diet.
We look forward to research on whether meat-eaters have shinier hair than vegetarians, and why. Incidentally, Professor Hatch, whose training is in zoology, uses similar techniques to determine the diet of birds and reptiles.