Obesity is not just about sugar: too much salt, not enough water

Inasmuch as educator, researcher and professor of medicineI have spent more than 20 years investigate the causes of obesityas well as related conditions such as diabetes, high blood pressure and chronic kidney disease.

In my many years of studying obesity and related health issues, I have observed that relatively little is said about two important pieces of this very complex puzzle: lack of hydration and excessive consumption of salt. Both are known to contribute to obesity.

Lessons learned from a desert sand rat

Nature provides a clue as to the role these factors play with the desert sand rat Psammomys obese, a half-pound rodent with a high-pitched squealer that lives in the salt marshes and deserts of North Africa. It barely survives by eating the stems of Salicornia – glasswort – a plant that looks a bit like asparagus.

Although poor in nutrients, the fleshy, succulent samphire of glasswort is filled with salt-rich water, in concentrations as high as those found in seawater.

Recent studies brought new knowledge 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 ingests into fructose, a type of sugar naturally present in fruits, honey and some vegetables.

This help the animal to survive when food and fresh water are scarce. Indeed, fructose activates a “survival switch” which stimulates the search for food, the food intake and the storage of fats and carbohydrates which protect the animal from starvation.

However, when the rat is brought into captivity and given the common rodent diet of around 50% carbohydrates, it rapidly develops obesity and diabetes. But if given fresh vegetables low in starch, the rodent remains thin.

The desert sand rat, also known as the fat sand rat, is actually a gerbil. It is found in Asia as well as in Africa.
Kristian Bell/Moment via Getty Images

My research, and the research of many other scientists over the decades, shows that many Americans behave unintentionally like a desert sand rat in captivity, although few are found in environments with limited food and water. They constantly activate the survival switch.

Fructose and our diets

As mentioned, fructose, a simple sugar, appears to have a key role in activating this survival switch that leads to fat production.

Small amounts of fructose, such as that found in an individual fruit, are not the problem – rather, excessive amounts of fructose are problematic for human health. Most of us get our fructose from table sugar and high fructose corn syrup. Intake of these two sugars totals about 15% of calories in the average American diet.

These sugars encourage people to eat more, which can lead to weight gain, fat accumulation and prediabetes.

Our bodies also produce fructose on their own – and experimental studies suggest it may be enough to trigger the development of obesity.

A spoonful of sugar, surrounded by sugar cubes, on a wooden table.
Table sugar and high fructose corn syrup are two of the culprits that can lead to weight gain and obesity.
ATU Images / The Image Bank via Getty Images

Since fructose is made from glucose, fructose production increases when blood sugar levels are high. This process occurs when we eat a lot of rice, cereals, potatoes and white bread; these are carbohydrates that quickly release glucose into the bloodstream quickly.

And in particular, the production of fructose can also to be stimulated by dehydrationwhich stimulates the production of fat.

fat provides water

Fat has two main functions. The first, which is well known, is to store calories for a later period when food is not available.

The other major but lesser known function of fats is to provide water.

To be clear, fat does not contain water. But when fat breaks down, it generates water in the body. The amount produced is substantial and roughly equivalent to the amount of fat burned. It is so important that some animals rely on fat to provide water during periods when it is not available.

Whales are just one example. While they drink seawater, they get most of their water from the food they eat. And when they go for long periods without food, they get their water mainly by metabolizing fat.

Hold the fries

The role of dehydration as a contributor to obesity should not be underestimated. It usually occurs after eating salty foods. Dehydration and salt intake lead to the production of fructose and fat.

This is why salty fries are particularly fattening. The salt causes a dehydration-like state that promotes the conversion of the starch in the fries to fructose.

Additionally, studies show that most people who are overweight or obese don’t drink enough water. They are much more likely to be dehydrated than those who are skinny. Their salt intake is also very high compared to that of lean people.

Research shows that obese people have high levels of vasopressina hormone that helps the kidneys retain water to regulate urine volume.

But recent studies suggest that vasopressin has another purpose, which is to stimulate fat production.

For someone at risk of dehydration or starvation, vasopressin can have a real survival benefit. But for those not at risk, vasopressin could cause most of the metabolic effects of excess fructose, such as weight gain, fat accumulation, fatty liver disease, and prediabetes.

Drink more water

Does this mean that drinking more water can help us lose weight? The medical community has often mocked at the claim. However, our research team found that giving mice more water slowed weight gain and development of prediabeteseven when the mice had high-sugar and high-fat diets.

There is also growing evidence that most people drink too little water in general, and increasing water intake can help obese people losing weight.

That’s why I encourage drinking eight large glasses of water a day. And eight is probably enough; don’t assume more is better. There have been cases of people drinking so much that “water intoxication” occurs. This is especially a problem for people with heart, kidney or liver problems, as well as those who have recently had surgery or are long distance runners. It is always a good idea to consult your doctor first about water intake.

For the desert sand rat, and for our foraging ancestors, a diet high in salt and water made sense. But human beings don’t live that way anymore. These simple steps – drinking more water and reducing salt intake – offer cheap, easy and healthy strategies that can prevent or treat obesity.

Richard Johnson is a professor of medicine at the University of Colorado’s Anschutz Medical Campus.


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