Scientific studies and media coverage are rife with warnings on how sugar, carbohydrates, saturated fat and lack of exercise contribute to obesity. And tens of millions of Americans are still overweight or obese in large part because of the classic Western diet and lifestyle.
As an educator, researcher and professor of medicine, I have spent more than 20 years investigating the causes of obesity, as well as related conditions such as diabetes, high blood pressure and chronic kidney disease.
Throughout my many years of studying obesity and related health conditions, I’ve observed that relatively little is said about two significant pieces of this very complex puzzle: lack of hydration and excessive salt intake. Both are known to contribute to obesity.
Lessons learned from a desert sand rat
Nature provides a clue to the role these factors play with the desert sand rat Psammomys obesus, a half-pound rodent with a high-pitched squeak that lives in the salty marshes and deserts of Northern Africa. It survives, barely, by eating the stems of Salicornia – the glasswort – a plant that looks a bit like asparagus.
Although low in nutrients, the glasswort’s fleshy, succulent sap is filled with water that’s rich in salt, at concentrations as high as what’s found in seawater.
Recent studies have provided new insights into why the desert sand rat might crave the salty sap of glasswort. Although this has not yet been proven specifically in the sand rat, it is likely that a high-salt diet helps the sand rat convert the relatively low amount of carbohydrates it’s ingesting into fructose, a type of sugar that occurs naturally in fruits, honey and some vegetables.
This helps the animal survive when food and fresh water are sparse. This is because fructose activates a “survival switch” that stimulates foraging, food intake and the storage of fat and carbohydrates that protect the animal from starvation.
However, when the rat is brought into captivity and given the common rodent diet of about 50% carbohydrates, it rapidly develops obesity and diabetes. But if given fresh vegetables low in starchy carbohydrates, the rodent remains lean.
My research, and the research of many other scientists over the decades, shows that many Americans unwittingly behave much like a captive desert sand rat, although few are in settings where food and water are limited. They are constantly activating the survival switch.