I’m frequently asked if sugar causes inflammation. The question seems simple enough, but there’s a lot jammed in there. My short answer? A high-sugar Western diet seems to be a key factor in creating systemic, needless immune activity. This is called chronic inflammation, and it’s linked to every chronic disease in the book.
The long answer requires more nuance. For most people, having a soda doesn’t “fire up” the immune system. No, the links between sugar and inflammation are more subtle, usually one or two steps removed from the resulting inflammation. Consider that:
- High sugar intakes lead to high blood sugar, a pro-inflammatory state.
- A high-sugar diet may preferentially feed inflammatory bacteria in the gut.
- Eating sugar (fructose in particular) can cause the liver to produce toxic levels of fat.
The terms “sugar” and “inflammation” are often thrown around with vague understanding and plenty of vigorous head bobbing, so today I want to clear things up. I’ll start with a brief rundown on sugar, dissect acute vs. chronic inflammation, and then cover 6 mechanisms by which sugar is linked to inflammation.
The Rundown on Sugar
Sugar is a vague term. It can refer to a variety of things including glucose, fructose, sucrose, galactose, high fructose corn syrup, or a significant other. The term “refined sugar” (or “added sugar”) is more specific, and refers to either sucrose (table sugar) or high fructose corn syrup—both of which are blends of the simple sugars glucose and fructose.
It’s added sugar that’s high in the Standard American Diet (SAD). How high? Believe it or not, the average consumption is about 15 to 20 teaspoons per day! Sugar-sweetened beverages (SSBs) account for the majority of most folks’ sugar consumption, so if you’re looking to cut back, that’s a great place to start.
It’s obvious that refined sugar is bad for us, but its link to inflammation is less straightforward. Next up is inflammation, and then I’ll explain how they’re related.
Acute vs. Chronic Inflammation
Much like salt, many people mislabel inflammation as inherently bad—but without it, you couldn’t heal from an injury or ward off infection. What’s all the confusion about? There are actually two different types of inflammation: acute and chronic.
Acute inflammation is a temporary immune response. Think of it as an army of immune cells mobilizing to handle an issue. The first soldiers to arrive are called inflammatory cytokines. They rush to the site and serve as signaling beacons for platelets, lymphocytes, neutrophils, and the rest of your immune system to get involved.
This response is how your body fights off pathogens, disease, infection, and heals wounds. And once the problem is handled, the troops go home. Without acute inflammation, every scrape would become horribly infected, so it’s often desirable. (Though not always, as in the case of traumatic brain injury.)
Chronic inflammation (aka, systemic inflammation) is never desirable. Like acute inflammation, it involves an immune response with cytokines and white blood cells. The difference is that there is no specific infection that needs to be neutralized. In other words, your immune system is perpetually confused—fired up when there’s no need to be. The consequences can be dire.
Most modern diseases—heart disease, cancer, Alzheimer’s, diabetes, you name it—have this in common. As chronic inflammation goes up, expected lifespan goes down. This is most obvious with heart disease: inflammation forms plaques in the arterial wall, which eventually break off to cause heart attacks and strokes. Some researchers believe that statins work not simply because they lower LDL particles (the initial domino in plaque formation), but also because they lower inflammation.
By now you’re probably wondering what causes chronic inflammation. Well, how much time do you have? Poor sleep, aging, cigarette smoking, alcoholism, lack of exercise, and a high intake of vegetable oils are just a few factors that top the list. I believe excess sugar consumption belongs on that list too.
6 Ways Sugar Can Cause Inflammation
When you look at observational data, you find that higher sugar intakes are correlated with higher levels of inflammation. For instance:
- In 244 healthy women, a high glycemic diet was associated with higher levels of C-reactive protein (CRP)—a marker of non-specific inflammation.
- Young children who drink more sugary beverages have more inflammation.
- American consumption of SSBs declined from 1999 to 2010, and CRP declined along with it.
These correlations aren’t enough to convict sugar on the charge of inflammation. But when you combine them with mechanistic data, the case grows stronger. With that in mind, here are six ways sugar may drive inflammation.
#1: By raising blood sugar levels
When someone consumes loads of sugar, that sugar ends up in their blood. And if they consume excess sugar frequently over the long term, their blood sugar stays chronically high.
High blood sugar (or hyperglycemia) is a pro-inflammatory state because glucose is a highly reactive molecule. Specifically, glucose reacts with oxygen, creating volatile compounds called reactive oxygen species. This oxidative stress, in turn, creates damage that provokes an inflammatory response.
#2: By disrupting gut health
Your gut is home to a vast colony of microbes called the gut microbiome. These microbes influence digestion, mood, and—relevant here—the immune response.
The research is preliminary (mostly in mice and test tubes), but scientists believe that certain classes of bacteria influence inflammation. For instance, excessive levels of Proteobacteria appear to trigger an inflammatory response in animals, while Bacteroidetes seem to have the opposite effect.
And in humans, a diet high in simple sugars was found to increase intestinal permeability. This is called leaky gut, and it results in particles slipping through the intestines and into the bloodstream. The confused immune system then attacks these particles, creating damage and even more inflammation. Sugar feeds bad bacteria which perpetuate this cycle.
#3: By impairing oral health
Eating sugar feeds a pathogenic oral bacteria called Streptococcus mutans (S. mutans). S. mutans then accelerates plaque formation, degrades teeth, and therefore causes cavities. But it isn’t just a cavity bug. It often gets into the bloodstream, triggers inflammation, and may increase the risk of heart disease.
#4: By increasing fat production in the liver
Humans have a special taste for fructose. This simple sugar (found in fruit, sucrose, and high fructose corn syrup) served us well in prehistoric times. It’s quick to be stored as fat, so it was useful in times of caloric scarcity. When we ran out of food, we could rely on our fat stores for energy.
In fact, we have a special mutation that shunts fructose to the liver for rapid conversion to fat. Back in the day, the apes that had this mutation were more likely to survive famines, and so it spread through the population naturally.
Humans carry this mutation to this day, only now it doesn’t serve us for the better. This fructose-to-fat conversion—which occurs whenever we slurp down a soda—has inflammatory consequences. Making all those fatty acids creates metabolites that likely increase oxidative stress and inflammation.
#5: By decreasing ketone production
When you consume sugar, your blood sugar and insulin levels rise. Rising insulin then decreases fat burning and ketone production. Where’s the link to inflammation? Ketones are anti-inflammatory.
Specifically, the ketone body beta-hydroxybutyrate has been shown to suppress the NLRP3 inflammasome—a signaling beacon of chronic inflammation.
#6: By promoting weight gain
The link between obesity and inflammation is complex. They tend to come together, but it’s not clear which is causative. What’s super clear is that high intakes of added sugar underlie both problems.
For starters, sugar is easy to overconsume. Our genes love sugar—remember that fructose used to confer a survival advantage—so our taste buds lap it up. Plus added sugar is less satiating than fat, protein, or starch, so you can put back a ton.
Then there’s the whole sugar-induced metabolic dysregulation I covered earlier. If you want to stay slim and non-inflamed, added sugar won’t help with those goals. So whether obesity causes inflammation or inflammation causes obesity, the takeaway is the same: sugar is not your friend.
Less Sugar, Less Inflammation
If you want to live a long and healthy life, it pays to eat an anti-inflammatory diet. Minimizing added sugar is a big step, but you should know that its only one piece of the puzzle. Sleeping well, exercising regularly, managing stress, and getting optimal amounts of vitamins and minerals are extremely important as well. For a broader look at what causes inflammation and how to reduce it, check out this article.