Researchers discovered that drinking unsweetened filter coffee may help control blood sugar levels through an interesting chain reaction in your gut. When you drink plain filter coffee, it changes the bacteria in your digestive system, specifically increasing a type called Veillonella. These bacteria produce a substance that helps your body manage blood sugar better. This study used genetic information from thousands of people to understand this connection. The findings suggest that the way you prepare your coffee—keeping it unsweetened and using a filter—might be an easy way to support better blood sugar control, which is especially important for people managing diabetes.

The Quick Take

  • What they studied: Whether drinking different types of coffee affects blood sugar control, and if gut bacteria are the reason why
  • Who participated: The study analyzed genetic data from large groups of people in the UK Biobank and an international microbiota database. No specific number of direct participants was mentioned, but the data came from thousands of people’s health records
  • Key finding: Drinking unsweetened filter coffee appears to increase helpful bacteria in your gut that produce a compound called propionic acid, which may help lower HbA1c (a measure of average blood sugar over three months)
  • What it means for you: If you drink coffee, choosing unsweetened filter coffee instead of sweetened versions might help your body manage blood sugar better. However, this is early research, and you should talk to your doctor before making major changes to your diet, especially if you have diabetes

The Research Details

This study used a special research method called Mendelian randomization, which is like a detective tool that uses genetic information to understand cause-and-effect relationships. Instead of asking people to drink coffee and watching what happens, researchers looked at genetic data from thousands of people to see natural patterns. They examined information from two large databases: the UK Biobank (which has health information on hundreds of thousands of British people) and the MiBioGen consortium (which focuses on gut bacteria genetics). The researchers traced a pathway: unsweetened filter coffee → changes in gut bacteria → better blood sugar control. They used statistical methods to make sure their findings were solid and not due to chance.

This approach is valuable because it avoids some problems with regular studies. People often remember their diet incorrectly, and it’s hard to do long-term studies where you control everything someone eats. By using genetic information, researchers can identify real cause-and-effect relationships without these problems. The study also looked at how coffee preparation matters—filter coffee without added sugar appears to work differently than other coffee types

The study used large, well-established databases with genetic information from many people, which makes the findings more reliable. The researchers performed sensitivity analyses, which means they checked their results in different ways to make sure they held up. However, because this is a genetic study rather than a direct experiment, the findings suggest a connection but don’t prove it works the same way in everyone’s body

What the Results Show

The main discovery was a clear chain of events: unsweetened filter coffee consumption is connected to increased amounts of a specific gut bacteria called Veillonella. This bacteria produces propionic acid, a compound that appears to help lower HbA1c levels (a measure of long-term blood sugar control). The connection was statistically significant, meaning it’s unlikely to be due to random chance. The study found that this pathway explains how coffee might help with blood sugar management. Importantly, the type of coffee matters—unsweetened filter coffee showed this benefit, while other coffee preparations did not show the same effect. This suggests that both the preparation method and avoiding added sugar are important factors.

The research highlights that the relationship between what we eat and our gut bacteria is complex and important for our health. The study shows that dietary choices don’t just affect us directly—they work through our gut bacteria to influence our body’s metabolism and blood sugar control. This opens up new possibilities for managing blood sugar through food choices rather than just medication

Earlier research has shown that coffee has benefits for metabolic health, but this study provides a new explanation for why. Previous studies suggested coffee was good for blood sugar, but didn’t explain the mechanism. This research adds an important piece of the puzzle by showing that gut bacteria are the middleman between coffee consumption and blood sugar control. It also confirms what some earlier work suggested: that how you prepare coffee matters, and unsweetened versions are better than sweetened ones

This study used genetic data rather than directly observing people drinking coffee and measuring their blood sugar, so while it suggests a strong connection, it doesn’t prove the effect works exactly the same in everyone. The study doesn’t tell us how much coffee you need to drink or how quickly you might see benefits. Individual responses may vary based on genetics, overall diet, and other health factors. The research also doesn’t account for all the different compounds in coffee or how they might interact with each person’s unique gut bacteria

The Bottom Line

If you drink coffee, choosing unsweetened filter coffee may support better blood sugar control (moderate confidence based on this research). This is especially relevant if you’re managing diabetes or prediabetes. However, coffee should be part of an overall healthy diet and lifestyle, not a replacement for medical treatment. Talk to your doctor or a dietitian before making significant dietary changes, particularly if you take diabetes medications

This research is most relevant for people with diabetes, prediabetes, or those concerned about blood sugar control. It’s also interesting for anyone who drinks coffee regularly and wants to optimize their health. People who don’t drink coffee shouldn’t feel they need to start based on this study alone. Those with caffeine sensitivity or certain health conditions should consult their doctor before increasing coffee consumption

Changes in gut bacteria can happen relatively quickly (within weeks to a few months of dietary changes), but improvements in blood sugar control typically take longer to measure—usually several weeks to months. HbA1c, which measures average blood sugar, changes slowly and is typically checked every three months. You might not notice immediate effects, but consistent habits over time are more likely to show benefits

Want to Apply This Research?

  • Track daily unsweetened filter coffee consumption (cups per day) alongside weekly HbA1c readings or fasting blood sugar measurements if you have a home glucose monitor. Note the type of coffee and preparation method to identify patterns
  • If you currently drink sweetened coffee or other coffee preparations, gradually switch to unsweetened filter coffee. Start by reducing added sugar or sweeteners, then experiment with filter brewing methods. Set a daily goal (e.g., one cup of unsweetened filter coffee) and log it in the app to build the habit
  • Create a monthly dashboard showing coffee consumption patterns alongside blood sugar metrics. Set reminders to check in with your doctor every three months to review HbA1c results and discuss whether your coffee habits are contributing to better blood sugar control. Track any changes in energy levels, digestion, or other health markers

This research suggests a potential connection between unsweetened filter coffee consumption and blood sugar control through gut bacteria, but it is not a substitute for medical advice or diabetes treatment. Individual results may vary based on genetics, overall diet, medications, and other health factors. If you have diabetes, prediabetes, or take medications affecting blood sugar, consult your healthcare provider before making significant dietary changes. This study provides interesting insights but should be considered alongside other evidence and professional medical guidance. Do not stop or change any diabetes medications based on this research without talking to your doctor first.