Salt: “supertasters” and how obesity impacts sensitivity

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New research from food scientists at Pennsylvania State University suggest that some people’s penchant for salt may be due to a broader hypersensitivity to taste. The researchers suggest that “supertasters” not only experience the taste of salt more intensely, but other flavors as well — meaning that they often rely on extra salt to overcome their experience of bitterness, for example. Meanwhile, researchers from the Medical College of Georgia may have uncovered one way that obese people become more sensitive to salt’s impact — and more susceptible to hypertension. The researchers say that excess body fat can increase inflammation, which, in a chain reaction, ultimately impacts how much salt is retained by a certain component of our kidneys.

Excess salt consumption has been linked to an increased risk for hypertension and heart disease, and public health officials have recently been leading a charge to reduce sodium content in manufactured foods — and our diets. Yet along the way to that goal, researchers are working to determine what might be some of the hurdles to weaning a nation inured to salt, and how we can counteract the physiological effects of increased salt sensitivity among obese Americans.

The research at Penn State, led by assistant professor of food science John Hayes, included 87 participants who were asked to sample a variety of salty foods, as well as their low-sodium equivalents. Roughly half of the group were men and half women, and none of the participants were smokers. Roughly one third of the participants were “supertasters,” while the rest had medium or low taste sensitivity.

The study, published in the June 16 issue of the journal Physiology & Behavior, found that, even though supertasters were more sensitive to salt, they tended to prefer products with higher amounts of sodium. In many cases, that was not solely because they enjoyed the salt, but also because high salt content helped block out other unpleasant flavors. As Hayes explained in a statement on the research:

“Cheese is a wonderful blend of dairy flavors from fermented milk, but also bitter tastes from ripening that are blocked by salt… A supertaster finds low-salt cheese unpleasant because the bitterness is too pronounced.”

While researchers and physicians have long known that obesity increases the body’s salt sensitivity (as opposed to the tongue’s), as well as inflammation and hypertension, the study by investigators at the Medical College of Georgia set out to determine what may be the underlying causes for these well known links between sodium and obesity. In research funded by the National Institutes of Health and published in the American Journal of Physiology Regulatory – Integrative and Comparative Physiology, Dr. Yanbin Dong and colleagues began with an understanding that, when the body retains excess fat, it begins producing additional proteins known as interleukin-6 (IL-6) that can increase inflammation.

When they in turn exposed mouse kidneys to heightened levels of IL-6, they noted a chain of events which ultimately caused a protein known as epithelial sodium channel (ENaC) to retain extra sodium, contributing to hypertension. As Dong explained in a statement about the findings:

“We found that in cells fed IL-6, ENaC gets activated and the cells take in more sodium. It is the last step of your salt reabsorption.”

The next step in this research is to determine whether obesity and salt reabsorption function similarly humans, but, if that is the case, researchers say they hold a clue to developing a simple urine test to identify those at greatest risk for this particular form of hypertension.