What happens to your blood sugar after drinking soda? Read this and you might rethink downing that second can of Coca-Cola. You probably already know that sugar consumption, in general, contributes greatly to weight gain and obesity, which in turn puts individuals at considerably greater risk of diabetes and heart disease. But did you know that not all sugary foods and drinks are created equal — even when their caloric content is similar?
Sugar-sweetened beverages (SSBs) like sodas appear to play the most ominous role in our Western diet’s high-added-sugars problem, not only because they are consumed in such high quantities, but also because the type of sugar (typically sucrose or high-fructose corn syrup) that these drinks contain appears to set off a particularly unhealthy chain of metabolic events.
Surging blood sugar (glucose) after soda consumption is but the tip of the iceberg in a long litany of chronic health problems that can ensue, including: Type 2 diabetes (T2D), other cardiometabolic disorders (hyperinsulinemia, dyslipidemia, hypertension and more), nonalcoholic fatty liver disease (NAFLD), bone loss, gastrointestinal (GI) disorders, kidney problems, gout and tooth decay.
What’s a sugar-sweetened beverage (SSB)?
Sugar-sweetened beverages (SSBs) are drinks with added sugars, including: non-diet soft drinks/sodas, flavored juice drinks, sports drinks, sweetened tea, coffee drinks, energy drinks, and electrolyte replacement drinks.
The types of sugars used to make them sweet vary, and include: brown sugar, corn sweetener, corn syrup, dextrose, fructose, glucose, high-fructose corn syrup, honey, lactose, malt syrup, maltose, molasses, raw sugar, and sucrose.
What’s wrong with too much sugar?
Having a normal blood glucose level is a key indicator of metabolic health, whereas abnormally high blood glucose levels are often linked to serious health issues. While blood glucose levels are in constant flux and they’re different for everyone, meaning that rising and falling levels throughout the day is normal, blood glucose levels that swing within too wide of a range, and for too long in your life, puts you at substantially greater risk of metabolic and cardiovascular disorders, including diabetes. (Learn more: The Link Between Blood Sugar and Diabetes.)
Blood glucose levels are impacted by a variety of factors — including genetics, your metabolic and physical health, the amount of sleep you get, how you respond to stress, and your level of physical activity. But your diet also plays a major role in your body’s “glycemic control” ability. Carbohydrates in foods that you eat break down into glucose and get released into the bloodstream. The rise in blood glucose triggers the pancreas’s beta ( β) cells to release the hormone insulin, which tells the cells throughout our body to absorb the glucose to use it for energy or store it for future use in our muscles or liver as glycogen. Any excess glucose is converted to fat and ectopically stored in liver, muscle and adipose tissues. (Learn more about insulin resistance, the functional impairment in your ability to move enough glucose to your cells, and how it can lead to diabetes.)
Clearly, a certain level of carbohydrates is necessary for good health, carbs being the body’s main source of fuel to power your muscles, your nervous system, and your brain. (Learn more: Confused About Carbohydrates?) However, consuming too many carbs can be unhealthy — especially if they are “low-quality carbs” (those lacking in nutrients and fiber) rather than healthy, whole-food, high-fiber carbs, like steamed broccoli. Low-quality carbs have high levels of fats, sodium and/or “added sugars” — and as such are the main culprits responsible for our nation’s high blood sugar levels and corresponding high incidence of non-communicable diseases (e.g., diabetes). Just one example of the large body of evidentiary research on this topic: a recent study of more than 100,000 participants found that those who had a diet high in heavily processed foods (with high levels of added sugars) were significantly more likely to develop type 2 diabetes.
Beware of added sugars
Sugar in the form of sucrose or high-fructose corn syrup, both of which are made up of nearly equal amounts of glucose and fructose, is added to numerous manufactured food products. In the United States, an estimated 15% of total energy intake is derived from these “added sugars” — with a higher proportion of over 20% among adolescents.
Seeing that these percentages rose steadily over the past 20 years, the USDA in Dietary Guidelines for Americans 2020–2025 reduced its recommended daily added sugar intake to less than 10% of calories per day, down from the 13% levels it recommended in 2005. The American Heart Association has proposed limiting sugar calories even more drastically, to 150 kcal/day for men or 100 kcal/day for women, which equates to no more than 6% of calories each day. Similarly, the World Health Organization, which officially advises that less than 10% of energy come from the consumption of “free sugars,” has also advised that a reduction to below 5%, or roughly 25 grams — or 6 teaspoons per day — would be even better. To put this into perspective, a 12-oz can of Coca-Cola contains about 10 teaspoons of sugar.
The leading sources of added sugars in the U.S. diet are processed and ultra-processed foods, including sugar-sweetened beverages, desserts and sweet snacks. According to one study, ultra-processed foods account for 90% of the added sugars we consume. See our report, The Truth About Processed Foods, for details on which foods are ultra-processed (and therefore the least healthy) versus those that are minimally processed (e.g., a can of beans or a loaf of whole wheat bread) and so still considered relatively healthy.
SSBs: Our largest added-sugars problem
Sugar-sweetened beverages (SSBs), including soda, which on average contribute approximately 7% of daily calories and nearly 50% of added sugars in the diet, according to a 2018 clinical review, comprise by far the largest added-sugars food source consumed by Americans. (Other major contributors to added sugar intake include candy and desserts, contributing approximately 4% to 9% of daily energy intake depending on age.) Approximately 66% of U.S. youths consume at least one SSB per day.
What’s so alarming about SSBs, soda and blood sugar?
Like other foods containing high concentrations of added sugars, SSBs, like sodas, cause your blood glucose levels to rise; and for individuals that consume them frequently and over a period of years (or shorter), perhaps exacerbated by other factors (including obesity, genetics, etc.), chronic metabolic conditions can ensue.
Not only are chronic post-meal (diet-induced) glucose spikes an independent risk factor for non-communicable disorders such as diabetes, they also contribute greatly to obesity. What’s particularly fascinating is the more recent understanding that genes are not as responsible for obesity as is a lifetime of high glucose-stimulated insulin secretion. The time of day your insulin is put to its biggest test is after a meal — the postprandial period, when people with insulin resistance have difficulty processing carbohydrates. Even if your fasting glucose is normal, individuals with higher levels of two-hour plasma glucose have a higher risk of developing diabetes. (See our report on Postprandial Blood Sugar to learn more.)
High-fructose corn syrup in soda: The problem, or just a factor?
Sodas are SSBs that contain very high concentrations of either high-fructose corn syrup (HFCS) or sucrose, the latter consisting of fructose and glucose molecules. Scientists continue to debate the relative roles that added glucose, sucrose and fructose (and fructose-derivatives) play in disease risk, morbidity and mortality. For example, a 2021 meta-analysis concluded that “chronic consumption of fructose is no worse or better than equivalent doses of sucrose or glucose for glycemic and other metabolic outcomes.” However, the authors also clearly pointed out that “we are not stating that consumption of sugar, especially as refined carbohydrates, is advisable or beneficial.”
Other studies, including a 2021 perspective, do single out the exponential increase of HFCS consumption as the prime culprit in the increased incidence of obesity and type 2 diabetes in countries who have adopted the Western diet — even if the mechanistic link has not been fully proven.
Regarding blood sugar control specifically, one study showed that HFCS consumption results in greater dose-normalized glycemia than equivalent doses of sucrose in humans. Another study found that “chronically high fructose intakes increase postprandial peripheral blood fructose concentrations and HbA1c levels, even as blood fructose concentrations remain low.”
Interestingly, a 2021 Swiss study found that daily consumption of beverages containing moderate amounts (comparable to those provided by commercial soft drinks/fruit juices) of either fructose or sucrose, but not glucose, increases hepatic FA synthesis in healthy men in a basal state. “SSB consumption (with ad libitum meals) influenced absolute macronutrient intake (i.e. decreased fat and protein intake) but did not increase total energy intake.” The authors went on to theorize that the mechanism they studied is “probably the first metabolic change induced by regular fructose-containing SSB consumption… the metabolic switch towards a higher lipogenic activity in the liver [that] may pave the way for further changes affecting metabolic health.”
Similarly, a 2021 paper points the finger at added fructose, from the exponential increase in HFCS consumption from SSBs, as a primary driver behind the increased incidence of obesity and type 2 diabetes, finding that “although dietary fructose was thought to be metabolized exclusively in the liver, evidence has emerged that it is also metabolized in the small intestine and leads to intestinal epithelial barrier deterioration.”
The bottom line: Most studies have correlated above-average consumption of SSBs like soda, whether it be because of HFCS or added sucrose, with increased risk for both cardiovascular mortality as well as nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2D), but they have not found that consumption of natural whole fruits and vegetables, and even fruit juices, at normal dietary levels, correlates with these same cardiometabolic indicators.
Other health problems associated with high soda consumption
While the above discussion centered on high blood sugar, glycemic control is but one parameter (albeit a major one) of the complex metabolic equation that involves triglycerides, insulin, tissue inflammation and gut disturbances. But it looks like SSBs are culprits in disturbing those other parts of metabolic health as well. A 2007 study found that consumption of > or = 1 soft drink per day was associated with increased odds of developing metabolic syndrome, obesity, increased waist circumference, impaired fasting glucose, higher blood pressure, hypertriglyceridemia and low high-density lipoprotein cholesterol.
Medical disorders associated with high SSB and soda consumption, many of which stem from the above conditions or are independently caused by other mechanisms, include the following:
- Obesity: Several large meta-analyses associate increased SSB consumption with increased body weight. While much, though not all, of this increased weight is likely due to increased total energy consumption, SSBs appear to increase cardiometabolic risk independently of adiposity.
- Insulin resistance and hyperinsulinemia: Even consumption of SSBs containing moderate amounts of fructose for a few weeks changes the serum fatty acid (FA) profile and induces hepatic insulin resistance.
- Dyslipidemia: Excessive fructose consumption has significant effects on lipid metabolism, contributing both to steatosis and to increased circulating triglyceride levels in the form of very low-density lipoprotein (VLDL). A 2021 study study investigated the metabolic effects of daily sugar-sweetened beverage consumption for several weeks in healthy lean men, revealing that such beverages (sweetened with the sugars fructose and sucrose, but not glucose) increase the ability of the liver to produce lipids, paving the way for further unfavorable effects on metabolic health.
- Cardiovascular disease: Daily SSB consumption has been associated with approximately 25% greater risk of developing coronary heart disease in both men and women compared with nonconsumers. Additionally, HFCS-sweetened but not sucrose-sweetened beverages specifically increase systolic blood pressure in humans. The intake and transport of fructose somehow interacts with the absorption of important electrolytes that can impact blood pressure.
- Nonalcoholic fatty liver disease (NAFLD): Fructose intake has been shown to result in increased gut leakiness and endotoxemia, simple steatosis and the progression toward more advanced forms of nonalcoholic fatty liver disease (NAFLD), including nonalcoholic steatohepatitis, fibrosis, and hepatocellular carcinoma. (See our Cancers section, below, for the strong link between fatty liver disease and colorectal cancer.)
- Bone loss: Consumption of high levels of caloric sweeteners composed mainly of fructose may be a risk factor for bone loss. While the mechanism is still unclear, it is apparent that an excessive intake of sweeteners tends to increase the incidence of bone fracture and osteoarthritis, decrease bone mineral density, or reduce the rate of bone mineral accrual, likely because the intake and transport of fructose somehow interacts with the absorption of certain minerals essential for bone health.
- GI disorders: The prevalence and severity of fructose malabsorption (sometimes called fructose intolerance) are directly proportional to dietary fructose levels and inversely proportional to age, being higher in infants (up to 90%) and young children (up to 67%), but still relatively high in healthy adults (~34%) and even greater in patients with functional GI disorders. Even average rates of fructose consumption are known to cause mild GI distress in healthy subjects. High-fructose diets have also been associated with irritable bowel syndrome (IBS).
- Cancers: In the NIH-AARP Diet and Health Study, which included 0.44 million participants aged 50–71 years, a high intake of added sugars was positively associated with esophageal cancer, while added fructose was specifically associated with an increased risk of small intestinal cancer. And while the association between excess fructose intake and other GI cancers remains to be firmly established, a 2022 study showed that fatty liver disease (FLD) was consistently associated with colorectal cancer (CRC) risk in the presence or absence of liver fibrosis, suggesting that the risk [for] CRC development may be elevated even in a mild form of FLD without progression to advanced fibrosis. As we discussed above, high fructose intake has been strongly linked to nonalcoholic fatty liver disease (NAFLD).
- Gout: A 2019 meta-analysis explored the adverse association of SSB and fruit juice intake with incident gout, which does not appear to extend to whole fruit intake.
- Kidney diseases: Research shows that SSBs (sweetened with high-fructose corn syrup) increase vascular resistance in the kidneys, likely due to simultaneous increases in serum uric acid and copeptin — and it’s an effect that cannot be attributed to the caffeine content or osmolality of the beverage. While the exact mechanisms have yet to be fully identified, it appears evident that people who regularly consume these SSBs are at a ~60% increased risk of developing chronic kidney disease. It has also been shown that high fructose consumption increases urinary stone formation, in part via effects on urate metabolism and urinary pH, and also via effects on oxalate. Individuals with metabolic syndrome are particularly at risk for kidney stone formation.
- Tooth decay and cavities: While all sugary foods sugars can alter and increase the bacteria found in the mouth and increase the likelihood of dental disease, SSBs such as sodas further compound the risk of disease because they are acidic by nature and the acidity can cause additional erosion to the teeth. Thus, there is a well-documented association between SSB consumption and tooth decay. The effects of SSBs on oral health begins when they are consumed at a young age, even in small amounts, and the risk of tooth decay increases over time.
If you can cut out only one food source from your diet — for the sake not only of your blood glucose management, but also for your overall metabolic, cardiovascular, skeletal and even dental health — that food source should be sugar-sweetened beverages (SSBs), like sodas, particularly those loaded with high-fructose corn syrup and/or sucrose. To get your needed carbs, instead focus on the consumption of high-fiber vegetables, whole grains (especially oats and barley), and low glycemic-index fruits. These higher-quality carbs, together with lean proteins and healthy fats, will help decrease your cardiometabolic risk factors while aiding you in weight management in order to reduce your risk of diabetes, cardiovascular and other diseases. So next time you reach for that can of Coke, think about what happens to your blood sugar after drinking soda — and all the other negative health benefits deriving from consuming so much sugar.