Why do sugary drinks lead to dehydration and mineral deficiencies?

When a person consumes sugar (glucose, fructose, sucrose), these sugars enter the bloodstream and increase the osmolarity of the plasma — that is, the concentration of dissolved substances. The body strives to maintain osmotic balance. An increase in osmolarity leads to the following processes:

• Osmotic extraction of water from cells.  Cells begin to lose water, releasing it into the intercellular and vascular fluid to dilute the excess sugar in the blood. This can cause thirst.
• Increased filtration in the kidneys.  Glucose is excreted through the kidneys. Normally, almost all glucose is reabsorbed in the renal tubules. However, at high sugar levels (even subclinical), a phenomenon known as glucosuria occurs — some sugar does not get reabsorbed and remains in the primary urine.
• Osmotic diuresis.  Glucose in the urine retains water due to the osmotic effect: the more glucose that enters the urine, the more water will be "pulled" along with it to dilute the sugar concentration. The result — increased urination (polyuria).
• Dehydration.  This process leads to the loss of fluids and electrolytes. Therefore, after consuming sweet drinks, a person often feels even thirstier, despite having drunk. This is a classic mechanism, for example, in diabetes (especially when uncontrolled), but it also occurs in healthy individuals under high sugar load.

That is why any sugary drinks — lemonades, juices, sweet tea — have a mild diuretic effect. With regular consumption of sweet beverages, the body can systematically lose water and minerals (sodium, potassium, magnesium), leading to hidden dehydration and an imbalance in electrolyte exchange.

Hence the well-known recommendation: in heat or physical exertion, sweet drinks do not quench thirst and can sometimes worsen dehydration.