A single 12-ounce can of Coca-Cola contains 39 grams of sugar, and most of the damage soda does to your body traces back to that one fact. That sugar, consumed in liquid form, hits your liver fast, drives fat accumulation, erodes your teeth, and raises your risk for heart disease, type 2 diabetes, and fatty liver disease. Diet soda sidesteps the sugar but introduces its own set of concerns.
What Happens to Sugar When You Drink It
The sugar in soda is roughly half fructose, often delivered as high-fructose corn syrup. Unlike glucose, which your cells throughout your body can use for energy, fructose gets processed almost entirely by your liver. When fructose arrives in large amounts and all at once (as it does from a can of soda), the liver converts it directly into fat through a process called lipogenesis.
This isn’t a slow, gradual effect. Fructose activates a cascade of signals in liver cells that ramp up fat production and create a self-reinforcing cycle: the more fat your liver makes, the more efficiently it makes even more. Over time, that fat accumulates in the liver itself, a condition called nonalcoholic fatty liver disease. The National Institute of Diabetes and Digestive and Kidney Diseases has linked excessive consumption of high-fructose corn syrup and other added sugars to this condition, along with obesity, diabetes, and heart disease.
The fat buildup in liver cells also interferes with how your body responds to insulin, the hormone that controls blood sugar. When insulin signaling breaks down in the liver, it becomes harder to regulate blood sugar throughout your body. This is one of the defining features of type 2 diabetes.
Diabetes and Heart Disease Risk
The numbers are specific. Research from Harvard’s T.H. Chan School of Public Health found that increasing sugary beverage intake by more than 4 ounces per day over a four-year period was associated with a 16% higher risk of developing type 2 diabetes in the following four years. That’s not even a full can. A standard can is 12 ounces, so the risk increase starts well below what many people drink daily.
The cardiovascular risk is even more striking. A 15-year study tracked by researchers at UCSF found that people who got 25% or more of their daily calories from added sugar were more than twice as likely to die from heart disease compared to those who kept added sugar below 10% of their calories. Soda is one of the largest single sources of added sugar in the American diet, so it plays an outsized role in pushing people past those thresholds. Current U.S. dietary guidelines recommend no more than 10 grams of added sugars per meal for adults and adolescents, and no added sugar at all for children under 11. One can of Sprite contains 38 grams, nearly four times the per-meal recommendation.
Your Teeth Are Dissolving in It
Tooth enamel starts to dissolve at a pH of about 5.5. For context, water is neutral at 7.0. Every common soda falls far below that enamel-safe threshold. Coca-Cola has a pH of 2.48. Pepsi is 2.46. Mountain Dew comes in at 3.14. Even relatively mild-tasting sodas like Canada Dry ginger ale register at 2.94. The only widely sold soda that comes close to the safe zone is A&W root beer at 4.80, and even that sits below the threshold.
Diet versions are slightly less acidic but still well within the danger range. Diet Coke has a pH of 3.22, and Diet Mountain Dew is 3.27. So even if you eliminate the sugar, you’re still bathing your teeth in acid every time you take a sip. The acid softens enamel on contact, and repeated exposure throughout the day (sipping a soda over an hour, for instance) keeps your mouth in a state where minerals are constantly leaching out of your teeth faster than saliva can repair them.
Liquid Calories Don’t Fill You Up
One of the more insidious problems with soda is that it adds calories without reducing how much you eat. When you consume sugar in solid form (fruit, bread, a cookie), your body registers that food and adjusts your appetite accordingly. Liquid calories largely bypass this system. Your stomach processes liquids differently than solids, and the speed at which sugary drinks pass through your digestive system means the hormonal signals that tell your brain “you’ve eaten enough” never fire with the same strength.
This means a 140-calorie can of soda gets added on top of whatever you were going to eat anyway. Over weeks and months, those surplus calories accumulate. For someone drinking one soda a day, that’s nearly 1,000 extra calories per week that their body never accounts for in its hunger signals.
Bone Density and Phosphoric Acid
Cola-style sodas contain phosphoric acid, the ingredient that gives them their sharp, tangy bite. High phosphorus intake, particularly when calcium intake is low, can weaken bones over time. The mechanism involves your parathyroid hormone: when phosphorus levels in the blood rise without enough calcium to balance them, your body releases more parathyroid hormone, which pulls calcium from your bones to restore balance. Animal studies confirm that a phosphorus-rich, low-calcium diet reduces bone mineral density through this process.
This is especially relevant for teenagers and young adults who drink soda instead of milk or other calcium-rich beverages during the years when their bones are still building density. The concern isn’t that one soda will weaken your skeleton. It’s that habitually choosing soda over calcium sources during critical growth periods sets you up for lower bone density later in life.
Diet Soda Isn’t a Clean Fix
Switching to diet soda eliminates the sugar and its metabolic consequences, but it introduces artificial sweeteners that affect your body in ways researchers are still mapping out. The most consistent finding involves your gut microbiome, the community of bacteria in your intestines that influences digestion, immune function, and metabolism.
A 2025 study published in Frontiers in Microbiology tested five common sweeteners on gut bacteria and found clear differences. Sucralose and saccharin (found in many diet sodas) significantly reduced microbial diversity. Sucralose was the most disruptive, enriching potentially harmful bacterial families while suppressing others to less than 10% of the total community. Another common sweetener, acesulfame K, initially appeared to increase diversity, but it fundamentally altered how bacterial communities were structured, reducing their interconnectedness in ways that suggest lower long-term resilience. These network disruptions persisted even after the sweetener was removed.
Natural sweeteners like xylitol and stevia-derived compounds were less disruptive and tended to promote beneficial bacterial groups. So not all sugar substitutes carry the same risk, but the ones most commonly used in major diet soda brands are the ones that performed worst in this research.
Why Soda Is Worse Than Other Sugary Foods
Plenty of foods contain added sugar, but soda concentrates several problems into one package. It delivers a large dose of fructose in liquid form, which means rapid liver processing and no satiety signal. It’s highly acidic, which damages teeth independently of its sugar content. It contains no fiber, protein, vitamins, or minerals to offset the metabolic cost. And it’s consumed in large volumes repeatedly throughout the day, something you’re less likely to do with cake or candy.
The speed and volume matter. Eating 39 grams of sugar from a handful of cookies takes time, involves chewing, and triggers some degree of fullness. Drinking 39 grams of sugar from a can of Coke takes a few minutes and leaves you ready to eat a full meal right after. That combination of high sugar delivery, zero nutritional value, and absent satiety signaling is what makes soda uniquely harmful compared to other sources of added sugar in the average diet.