New evidence is constantly coming out debating the benefits and risks of alcohol, whether low-carb or low-fat diets are better, and how much water we really need to drink. But there’s one thing experts seem to agree on: Excess added sugar is not good for your health.
Natural vs. added sugar
Sugars that occur naturally in food—fructose and glucose in fruit, lactose and galactose in dairy products, maltose in some sprouted grains, and sucrose in sugar beets—aren’t the problem here. Added sugar refers to the sweeteners in processed foods, most commonly sweetened beverages, candy, and baked goods. The American Heart Association (AHA) recommends that men consume no more than 9 teaspoons (36 grams) of added sugar a day, women no more than 6 teaspoons (25 grams). On average, Americans consume 17 teaspoons (68 grams) a day—the equivalent of 60 pounds of added sugar a year.
It’s not hard to overindulge in added sugar. A single 12-ounce can of cola, with 39 grams of added sugar, already exceeds the daily recommended limit. A classic sugar doughnut has about 13 grams. Many breakfast cereals contain 12 (or more) grams of added sugar per serving—even “healthy” cereals may have more than 8 grams. And many foods you might not think of as sweet contain surprising amounts of sugar: One tablespoon of ketchup, for instance, has 5 grams of added sugar. A half-cup of bottled tomato sauce may contain 7 grams. Even some breads and salad dressings can set you back 3 grams per single slice or tablespoon, respectively.
Sugar in packaged foods “hides” behind many names, including corn syrup, high-fructose corn syrup, evaporated cane juice, dextrose, agave, fruit juice concentrate, honey, brown rice syrup, sorghum syrup, maple syrup, blackstrap molasses, coconut sugar, and turbinado sugar. The list goes on and on. Some may sound healthier than others—but are not. The “Added Sugars” line on a product’s Nutrition Facts label tells you how many grams there are per serving, which can help you stick to the daily recommended limits.
The ills of added sugar
Sugar can be harmful in all the ways you’d expect—and some you might not. In the “not surprising” category, sugar causes cavities and is a major contributor to diabetes and obesity. In a 2023 review article in BMJ, which examined 73 meta-analyses and 83 health outcomes from more than 8,000 studies, the researchers found strong evidence linking dietary sugar consumption to an increased risk of endocrine and metabolic problems (like overweight and obesity, high cholesterol, and type 2 diabetes), cardiovascular problems (including heart disease and stroke), and seven cancer-related outcomes (including breast, prostate, and pancreatic cancers, as well as overall cancer risk). Excess sugar intake, especially of high-fructose corn syrup, is also a significant factor in fatty liver disease. No reliable evidence shows any health benefits of consuming added sugar.
Added sugars may increase the risk of these conditions in several ways—for example, by increasing oxidative stress, impairing the body’s ability to regulate insulin, increasing triglycerides (fats in the blood), and raising blood pressure. But one area that’s receiving a lot of attention these days is inflammation. Researchers are looking into how added sugar can increase inflammation, along with the health problems inflammation can cause.
For example, a review article in Biomedicines in 2021 suggested that overconsumption of added sugar can disrupt the gut environment, leading to chronic inflammation that can cause heart arrhythmias. This is referred to as the heart-gut axis, and it’s just one of the ways that added sugar could be wreaking havoc with our health.
The sugar/inflammation link
When you consume added sugar, your body—which can view it as a foreign substance that needs to be removed—increases production of cytokines (proteins that trigger the immune system to help the body heal). This immune response is helpful when we actually need to recover from something. When it’s triggered by habitual sugar consumption, however, the result can be low-grade, chronic inflammation—which can manifest in many ways, such as pain, chronic fatigue, mood disorders, gastrointestinal problems, and weight gain or loss. But another big concern is the possible connection between added sugar, inflammation, and chronic inflammatory diseases, which as a group are the most common cause of death worldwide. These include heart disease, stroke, respiratory disease, cancer, obesity, and diabetes.
Beyond the more obvious
Inflammation—including that caused by added sugar—is associated with an increased risk of other health problems as well. Among them:
- Impaired bone health. Bone health generally diminishes as we age, but inflammation may help accelerate the problem. A 2023 study in Scientific Reports examined data from 767 adults involved in the Midlife in the United States (MIDUS) study. Researchers analyzed markers of inflammation in the blood and found that one, interleukin-6, was significantly higher in people who also had reduced bone mineral density and strength in the femoral neck (hip area). The researchers point to previous studies that also found a link between several inflammatory markers and fracture risk.
- Inflammation may increase the risk of osteoporosis by signaling the body to engage in more bone resorption (a process in which minerals are removed from bones and released into the bloodstream) but not the mineral rebuilding process known as bone remodeling.
- Some studies also point to ways that sugar may contribute to weakened bones besides through inflammatory processes. A 2021 meta-analysis in the Nutrition Journal, for instance, linked sugar-sweetened beverages, notably sodas, to lower bone mineral density. One reason, the authors postulated, is that excess sugar—in the form of high-fructose corn syrup—may impair kidney function and cause mineral imbalances, and this could adversely affect bone health.
- Other researchers have proposed that sugar may increase osteoporosis risk by lowering levels of vitamin D, which reduces absorption of calcium in the intestines, and by increasing blood sugar, which may impair bone formation. Excess sugar consumption can also cause fat cells to accumulate in the bone marrow, weakening the structure of bones. And, of course, people who consume a lot of sugar may also have poor diets that do not provide enough bone-protective nutrients.
- Cognitive dysfunction. Consuming too much added sugar may affect brain function. A 2024 review article in Nutrients looked at 65 clinical trials that tested the immediate and short-term effects of sugar consumption. Not too surprisingly, since the brain uses sugar (in the form of glucose) as a primary source of energy, the majority of these trials showed a benefit in memory, attention, and processing speed in the moment. However, 11 observational studies that the researchers also analyzed linked long-term, chronic overconsumption of sugar with reduced cognitive function, specifically executive function and memory.
- Again, inflammation may play a role. A review article in the International Journal of Molecular Sciences in 2022 points to several studies showing that inflammation in the brain (neuroinflammation) is associated with an increased risk of cognitive decline and dementia. The authors explain that inflammation is a reaction of the central nervous system to stimuli that the body views as dangerous, such as excessive sugar. The resulting immune response can lead to reduced functioning in the central nervous system, which can contribute to problems with memory and cognition.
- Autoimmune disorders. It certainly makes sense that inflammation would be associated with autoimmune disorders, which occur when the body mistakes something harmless for something harmful and triggers an inappropriate immune response. As a result, the body attacks healthy tissue, and a number of different conditions can occur.
- A 2022 review article in Frontiers in Immunology looked at the association between sugar and several inflammatory conditions. For instance, some studies have shown that sugar-sweetened beverages can play a role in rheumatoid arthritis, possibly by triggering the release of inflammatory cytokines and also damaging healthy flora in the gut. One survey found that women who drank one or more sugar-sweetened beverages a day had an increased risk of rheumatoid arthritis compared with women who didn’t drink them.
- Inflammatory bowel disease (IBD). This, of course, is likely to be affected by factors that increase inflammation. While genetics largely determine who’s at risk for IBD, lifestyle and diet may play important roles as well. A study in 2022 that looked at data from 121,490 participants found that over a 10-year period, those who drank more than one sugar-sweetened beverage a day were at significantly higher risk of developing IBD than those who did not drink these beverages. (No increased risk was associated with drinking artificially sweetened beverages or natural juices.) According to some dietary surveys, about 10 percent of people with IBD believe their symptoms flare up after consuming sweet foods or drinks.
BOTTOM LINE: Sugars that occur naturally in whole fruits and dairy—and to a lesser extent in vegetables and grains—do not appear to cause inflammation and, importantly, are accompanied by other healthful components, like vitamins, minerals, phytochemicals, and fiber. But sugars that have been added to processed foods have nothing redeeming about them and are best avoided whenever possible. Look for unsweetened versions of foods you tend to consume the most (such as unsweetened applesauce, unsweetened plant milks, and plain yogurt). An occasional sweet treat is fine, of course, but try to keep your added sugar consumption under the AHA’s recommended daily limit of 36 grams for men and 25 grams for women.
