Thursday, March 22, 2018

Could Salt Cause Obesity?

Could a high-salt diet lead to obesity?

Intuitively it makes sense. Most populations still eating traditional diets do eat salt, but often not as much as is found in Western diets, and such populations have low rates of diabetes. When they move from rural to urban environments and are exposed to salty Western food, they tend to gain weight.

(I did once read about an isolated group somewhere in South America, maybe the Yanomami, that didn't use salt; instead they burned a plant to get a calcium compound and used the ashes to flavor their food. When the anthropologists offered them some salty food, they said yuch and threw it away. But by the next day they'd changed their mind and were soon begging for more. I can't find the article I read, and perhaps the writer was exaggerating, but it does suggest that salt is addictive.)

If you don't think salt is addictive, try to eat just one potato chip.

It's been found that salt increases appetite, and now there's some scientific evidence that salt could lead to obesity through increasing leptin resistance. Leptin turns down your appetite when your fat stores are sufficient for your needs, and if you have leptin resistance, you have a big appetite even though your body is already storing plenty of fat.

For those interested in the mechanism, it seems that salt increases to aldose reductase pathway in the liver and hypothalamus. (The aldose reductase pathway is also involved in some diabetes complications.)

This pathway results in the production of fructose, which then causes insulin resistance. And blocking fructose metabolism blocks the effects of a high-salt diet.

In humans, a high-salt diet causes insulin resistance after only 5 days, and this study showed that in Japan, salt and calorie intake were correlated. In mice, a high-salt diet makes the mice eat more than usual. In the Japanese study in humans, the researchers showed that salt intake can be shown to be correlated with BMI, and high salt intake predicted diabetes and nonalcoholic fatty liver disease.

Could it be that too much salt, rather than too much fat or too much carbohydrate, is the real reason for the rise in obesity in America? Most Americans eat a lot of their meals away from home. And restaurant food and street food tend to be salty as well as sweet and fatty. If the salt makes you eat more, then you get more sugar and fat and calories, and you put on weight.

We all know that correlation does not mean causation, but when there's some proof of a mechanism, it becomes more likely.

Wouldn't it be ironic if it turns out that it's salt that is driving the increase in obesity? Of course you need calories to gain weight, but if the salt makes you eat more calories, then we can blame the salt.

And the fix is obvious.

1 comment:

  1. Over eating salty French Fries surely will cause weight gain.