How Coffee (Mostly) Improves Type 2 Diabetes Risk Factors

You might not think of your morning cup of joe as a health drink, but it’s likely that coffee — and the caffeine inside it — is helping your metabolism. Studies have repeatedly found that coffee drinkers have lower type 2 diabetes risks, and that the beverage is associated with related health benefits like weight loss.

Coffee has a curious effect on blood sugar: Caffeine can cause glucose spikes in the short term, but appears to improve glucose metabolism in the long term. Experts are still investigating how it works and what it means for people with diabetes.

Can coffee help you lose weight, boost your insulin resistance, and improve your blood sugar management? Diabetes Daily will walk you through the science.

Coffee Lowers the Risk of Type 2 Diabetes

People that drink coffee are less likely to have type 2 diabetes. Several major studies have found the association, such as this 2014 articles published in Diabetologia. Researchers followed over 100,000 American adults for years, and found that those who increased their coffee consumption by more than one cup per day reduced their risk of diabetes by 12 percent; those who decreased their consumption by more than one cup increased their risk by 18 percent.

Wider investigations have confirmed the link. In 2018, a meta-analysis in Nutrition Reviews considered the results of 30 studies, combining data from over one million participants. The authors found that every additional cup of coffee per day reduced the risk of type 2 diabetes by 6 percent.

Epidemiological studies like these are not considered definitive evidence, in part because the associations may reflect complex confounding factors rather than simple biological causation. For example, maybe coffee doesn’t make people healthier, but instead appears misleadingly healthy because Americans who don’t drink coffee typically drink more juice or soda?

But alternative methods of studying the topic have tended to suggest that there is a real causal relationship between coffee and metabolic health. A 2019 review of clinical trials — shorter controlled experiments in which volunteers are instructed to drink more or less coffee — found two or more weeks of increased coffee consumption improved glucose metabolism.

A clever new study of the topic was published in March, 2023, by the British Medical Journal. An international team of researchers hoped to take a fresh angle in assessing whether or not caffeine truly offers protection against type 2 diabetes and related cardiometabolic conditions.

So, rather than asking study volunteers about their coffee consumption, the researchers found people with a genetic tendency to metabolize caffeine slowly. Caffeine lingers in the bloodstream of people with this genetic variant, giving it a more powerful effect. These individuals are “exposed to higher caffeine concentrations throughout their life” even when they consume less of it.

As expected, people with slow caffeine metabolism were found to be slightly leaner and have a lower risk of type 2 diabetes than those without the genetic variant. Statistical analysis revealed that about half of the reduction in diabetes risk was due to the difference in body mass index — the rest, presumably, was due to the direct metabolic effect of caffeine itself.

How Coffee Helps the Metabolism

It’s one thing to find a statistical association between drinking coffee and certain health outcomes, but it’s quite another to explain why it’s happening. Experts aren’t quite sure how coffee and caffeine exert their effects on the metabolism, but they’ve got some guesses.

Caffeine increases thermogenesis.

Thermogenesis is the process by which your body burns energy to create heat and keep itself warm. Coffee really does increase your core body temperature, possibly by activating your brown fat. And though black coffee itself has zero calories, it takes calories to create that warmth.

A widely-cited 1989 experiment shows just how powerfully caffeine can kick your metabolism into action. Volunteers that consumed 100mg of caffeine, about the same amount found in a single cup of coffee, burned an additional 3-4 percent more calories over the next 150 minutes. When they repeatedly consumed caffeine over 12 hours, they burned 8-11 percent more calories during the interval. For lean individuals, it was a difference of 150 calories, though formerly obese participants experienced a weaker effect.

Caffeine increases fat oxidation

Fat “oxidation,” is, basically, fat burning. And caffeine boosts the process.

Caffeine has long been known as a performance-enhancing substance, a reputation confirmed by recent studies. But it’s not just for athletes. A 2022 systematic review and meta-analysis found that caffeine has “a highly significant but small effect” to increase fat metabolism, during both exercise and rest, no matter the fitness level of the drinker.

Coffee may especially energize fat oxidation in the liver, which can have an outsized effect on metabolic risks. Excess fat in the liver is highly associated with metabolic dysfunction and type 2 diabetes; burning excess liver fat is likely especially healthful.

Coffee helps you feel full

Many dieters believe that coffee helps to reduce their appetites, a notion that some scientific study has backed up. A 2017 review, for example, found that people eat less food if they’ve had caffeine 30 minutes to four hours before, and a 2014 experiment found that 3 cups of coffee per day led to weight loss and enhanced feelings of fullness. A 2022 study found that coffee didn’t help overweight and obese volunteers to feel fuller, but it did cause them to eat less.

In short, coffee may help you eat less, just one reason why coffee has been celebrated for its ability to help produce weight loss.

Coffee may aid the microbiome

Scientists are still only scratching the surface of the microbiome, the collection of dozens of trillions of microscopic organisms that live in our body and interact with our health in surprisingly complex ways.

Though the research is still very preliminary, there’s some evidence that coffee can improve the health of the gut microbiome, leading to higher levels of beneficial bacteria and lower levels of potentially harmful bacteria. Coffee may also help improve your Firmicutes/Bacteroides ratio, a measure of gut microbiome health; a bad ratio is associated with obesity and the western diet.

Coffee is an anti-inflammatory and an antioxidant

Coffee is full of anti-inflammatory compounds and is known to reduce inflammation. Why does that matter for people with diabetes? Type 2 diabetes is almost always accompanied by and may even be partially caused by chronic low-grade inflammation. It’s possible that coffee could slow the progression of diabetes by addressing this inflammation. Coffee drinkers also have higher levels of adiponectin, a hormone that decreases inflammation and increases insulin sensitivity.

Coffee is also full of antioxidant compounds. In fact, coffee may be the single greatest antioxidant contributor to the human diet., You may be aware that antioxidants help the body by scavenging free radicals, “dangerous molecules that attack good molecules that promote essential body functions,” according to Everyday Health. It’s less well-known that hyperglycemia promotes the creation of free radicals, suggesting that antioxidants may be especially helpful for people with diabetes.

Coffee may preserve the beta cells

Beta cells in the pancreas create and release insulin when the body needs it, but people with type 2 diabetes experience some level of beta cell decline and failure, leading to high blood sugars. A 2021 article in Nutrients argued that phytochemicals in coffee “support the preservation of pancreatic beta cell function … during periods of high insulin secretion,” and “prevent the formation of cell-toxic amyloids,” dysfunctional proteins “critical” to the progression of type 2 diabetes.

Coffee Also Improves Overall Health

It’s not just diabetes and metabolic risks — coffee appears to have positive health effects across the board.

In 2017, the British Medical Journal published an “umbrella review” that aimed to synthesize multiple meta-analyses concentrating on coffee’s many different health effects, combining and analyzing data from potentially thousands of studies. The bottom line? Coffee does more good than bad for most adults, and the people that drink the most (three to four cups per day) enjoy the biggest benefits. These findings were consistent in different parts of the world and in different types of people.

Coffee consumption was found to be associated with a breathtaking range of positive health outcomes, including lower risks for metabolic diseases such as diabetes, cardiovascular disease, multiple specific cancers, liver diseases, and mental health conditions (such as depression and Alzheimer’s disease).  Coffee consumption even significantly reduced the risk of early death.

Meanwhile, there was “no consistent evidence of harmful associations between coffee consumption and health outcomes,” with two exceptions: Pregnant women and women with a heightened risk of fracture may be better off minimizing their coffee intake.

But Coffee Also Causes Short-Term Glucose Spikes

With all this evidence of positive health effects, it may seem like coffee should be a no-brainer for people with diabetes. Not so fast…

If you are particularly careful with your glucose management — and especially if you use a continuous glucose monitor — it’s possible that you have noticed that coffee can actually raise your blood sugar, at least in the short term.

This surprises most people. Coffee, all by itself, has nearly zero carbs, so it shouldn’t really have any impact on your blood sugar. And as we learned above, coffee is supposed to have a positive effect on the metabolism, not a negative one.

The primary cause is caffeine. Research shows that caffeine causes blood glucose spikes in patients with diabetes. The CDC agrees, listing coffee among other surprising things that can raise your blood sugar.

Lisa McDermott, RD, CDCES, a diabetes specialist with the Pittsburgh-based Allegheny Health Network, told Everyday Health that “some people with type 2 diabetes can drink all of the caffeine they want, while others see blood sugar levels spike with just one cup of coffee.”

This factor makes coffee potentially troublesome for people with diabetes, and it’s probably impossible for any one person to know if the short-term risks outweigh the long-term benefits.

If you experience a coffee-induced blood sugar rise that is consistent, predictable, and significant, you might consider a strategy to counteract it — we have ideas in our detailed article on coffee and blood sugars.

Demi Deherrera/Unsplash

Beware of Added Carbs in Coffee Drinks

It should go without saying, but it’s important to remember that added sugar in coffee (including natural sweeteners such as honey and agave syrup) can have a huge effect on blood sugar.

Milk is also a sneaky contributor to coffee carb and fat counts. An extra-large latte can have up to 25 grams of carbohydrates, mostly from the sugars found in milk, not to mention a sizeable amount of saturated fat. Alternative milks, such as soy and almond milk, often include added sugars to mimic milk’s natural sweetness.

If you prefer flavored coffee drinks, whether hot or cold, be very careful to check the nutrition facts. Beverages from places like Starbucks and Dunkin’ can pack in an amazing amount of sugar.

One cup of black coffee has nearly zero grams of carbohydrates, but a Starbucks Grande Frappuccino has an incredible 50 grams, more than a can of soda. Having coffee beverages that are high in saturated fat, sugar, and calories on a regular basis can contribute to weight gain, insulin resistance, and the progression of type 2 diabetes. Such beverages are almost certainly doing much more harm than good.

How Much Coffee Should You Drink?

Enjoy as much coffee as you like, but it might be wise to limit yourself to four cups per day.

The massive 2017 BMJ review suggested that coffee’s benefits are maximized at “three to four cups a day.” That recommendation dovetails with the USDA’s latest Dietary Guidelines (PDF), which suggest an upper limit of 400 mg of caffeine per day, slightly more than the amount found in four cups of coffee.

And if you don’t like coffee, don’t sweat it. Few doctors would advise all of their patients to start drinking more coffee simply for its protective qualities. If this article suddenly has you thinking that coffee is a cure-all, please remember that coffee’s health benefits are likely to be subtle — you can’t expect a cup or two to revolutionize your health.

Women who are pregnant or have a heightened risk of fractures are advised to drink less coffee than others.

How About Decaf?

Some of the science discussed in this article focuses on caffeine, rather than coffee itself. So what about decaf? Does decaffeinated coffee also protect against metabolic disease?

It might! Studies like this 2014 systematic review and meta-analysis found that decaffeinated coffee reduces type 2 diabetes risks just as well as caffeinated. Other major reviews have come to the same conclusion.

Coffee is a complex brew of many different active components, of which caffeine is only one. It’s entirely possible that coffee’s other components are largely responsible for the drink’s positive metabolic health effects.


It seems clear that regularly drinking coffee, including decaf, helps reduce the risk of type 2 diabetes and many other health conditions. Coffee — at least when it’s not loaded with added sugars and other add-ins — might be reasonably considered a health drink.

There are many ways that coffee may aid metabolism, including by raising your fat-burning rate and helping you eat less.

However, some people with diabetes experience higher blood sugar levels after drinking coffee, which can make the beverage potentially troublesome. If you’re curious about how much coffee you should be drinking, ask your healthcare provider to help you balance the risks and benefits.

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