Salt increases thirst only in the very short term and then actually reduces it and makes you hungry. That’s the surprising finding based on recent studies. Although eating salty foods leads to more fluid consumption for an hour or two, the process reverses within 24 hours—you become less thirsty and your body starts to conserve water and produce more of it internally. It needs more fuel—that is, food—to boost internal water production, so you get hungrier and eat more. So salt actually raises appetite more than it increases thirst.
What happens as salt consumption rises from six grams a day to 12 grams a day is that people report feeling hungrier even though they are eating exactly the same amount of food. This may be because the body’s levels of glucocorticoids increase with higher salt intake. Glucocorticoids reduce muscle mass and increase fat mass, and this appears to result—in complex ways that have yet to be fully studied—in greater hunger that leads to more food consumption so that the body can produce more water.
Over time, elevated levels of glucocorticoids lead to muscle wasting, osteoporosis, diabetes and other metabolic problems. So there may be another reason to avoid high-salt consumption, which already is linked to high blood pressure that can result in stroke, heart attack and kidney disease.
But the findings about salt and thirst—that more salt leads to less fluid consumption and greater food consumption in humans—were wholly unexpected. And they were confirmed by a mouse study. Healthy young mice increased their energy intake by 25% to 30% on a high-salt diet—compensating for salt-driven increases in energy expenditure, which apparently made them hungry. This could mean that high-salt diets lead to obesity. Hunger from higher-salt consumption can lead to increased food intake, creating a chronic situation where the increase in energy consumption exceeds energy expenditure, resulting in obesity. But this has yet to be shown conclusively.