An ice-cold cola sure hits the spot sometimes, but that blast of sugar does a number on your body. Downing a can of soda sends your body into a frenzy—here’s why you might want to stick with water or seltzer next time you need to rehydrate.

DID YOU KNOW THESE 10 SECRET FACTS ABOUT COCA-COLA?

Crack, fizz, gulp: Within the first ten to 15 minutes of that cola, your intestines mainline that sugar to your blood, spiking levels of glucose—blood sugar. That’s a lot of quick energy, and to manage the onslaught, multiple organs in your body kick into overdrive so you can process that sugar.

Your pancreas releases insulin to help transport the sugar (which is a carbohydrate) to your muscles for energy. But that soda contains much more sugar than your muscles need. “When an individual drinks a 20-ounce soda, they are getting an entire meal’s worth of carbohydrates through liquid,” explains Meltem Zeytinoglu, MD, MBA, an endocrinologist and assistant professor of medicine at the University of Chicago Medicine. “In most cases, this soda is consumed in addition to a meal, so the additional carbohydrates will need to be processed. This extra sugar, instead of being stored in muscle tissue, gets converted to fat in the liver.”

Your kidney also comes into play by getting rid of excess sugar through your urine. That means your body loses water, which, along with the diuretic effect of the caffeine in the soda, increases your risk of dehydration. The sugar and caffeine in soda is “quite the unhealthy combination,” says Dr. Zeytinoglu. Be sure to check out these 23 infused water ideas that’ll make you forget about soda.

Then there’s the issue of one soda never really being enough: According to a Princeton study, when researchers fed hungry rats a sugary solution, their brains released dopamine, a chemical that triggers motivation and reward, which can become addictive. And according to a National Institutes of Health study, sugar can be addictive in humans, too; the theory is that we’ve evolved as a species to instinctively value quick, high-carb, high-calorie foods, say the researchers.

The good news is you don’t have to banish sodas completely. “The most important thing to remember is that portion control matters,” says Cordialis Msora-Kasago, MA, RDN, a registered dietitian nutritionist in Los Angeles, CA, and spokesperson for the Academy of Nutrition and Dietetics. “An occasional soda is not going to have a significant impact on your health. It’s when it becomes a regular habit that [it’s] a problem. Look for other non-caloric beverages you enjoy, like iced tea, water and infused waters.” Next, read about some more reasons to cut back on all soda (including diet).