Scientists reviewed 11 studies to understand how eating healthy foods and exercising can help people with type 2 diabetes by changing the bacteria in their gut. They found that when people followed healthy diets—sometimes combined with exercise—the “good” bacteria in their stomachs increased, which helped their bodies control blood sugar better and reduced inflammation. The bacteria changes seemed to work by improving how the body processes fats and amino acids. While these results are promising, the researchers noted that the effects sometimes didn’t last long and depended on keeping up with the healthy diet.

The Quick Take

  • What they studied: Whether eating healthy foods and exercising can help people with type 2 diabetes by changing the bacteria living in their digestive system
  • Who participated: 319 adults total across 11 different research studies, most of whom had type 2 diabetes or were at risk of developing it
  • Key finding: Healthy diets increased good bacteria in the gut that help control blood sugar, and these bacteria changes were linked to better diabetes control and less body inflammation
  • What it means for you: If you have type 2 diabetes or prediabetes, eating a healthy diet may help by improving your gut bacteria, which could make it easier for your body to manage blood sugar. However, you need to stick with the healthy eating to keep these benefits going.

The Research Details

Researchers searched three large medical databases for studies published through September 2024 that tested whether diet and exercise changes could improve gut bacteria in people with type 2 diabetes or prediabetes. They found 11 studies that met their standards—6 were randomized controlled trials (the gold standard where people are randomly assigned to different groups) and 5 were quasi-experimental trials (similar but with slightly less rigorous design). All 11 studies looked at dietary changes, and 3 also included exercise programs. The researchers carefully checked the quality of each study using established scientific tools and rated how confident they could be in the overall findings.

This approach is important because it combines information from multiple studies to get a clearer picture than any single study could provide. By looking at how gut bacteria changed and how those changes connected to better blood sugar control, researchers could understand the actual mechanism—the ‘why’ behind why diet and exercise help diabetes. This helps doctors and patients understand that these lifestyle changes work partly by improving the helpful bacteria in the digestive system.

The studies included were rated as moderate quality, meaning they were well-designed but had some limitations. The sample sizes were relatively small (the 11 studies combined only had 319 people), which means the results might not apply perfectly to everyone. The studies used different types of diets and exercise programs, making it harder to compare them directly. However, most studies used solid methods to measure gut bacteria and track blood sugar changes.

What the Results Show

When people followed healthy diets, the good bacteria in their guts increased significantly. Specifically, bacteria that produce short-chain fatty acids (special compounds that help the body work better) became more abundant. Two types of beneficial bacteria—Faecalibacterium and Akkermansia—showed the biggest increases. The overall diversity of bacteria also improved, meaning more different types of helpful bacteria were present. These changes in bacteria were connected to better blood sugar control and lower inflammation markers in the blood.

The studies showed that the ratio between two major bacterial groups (Bacillota and Bacteroidota) improved with healthy eating. This ratio is important because an imbalanced ratio is linked to diabetes and obesity. When people ate healthier, this ratio shifted toward a more balanced state. The bacteria also started producing more helpful metabolites (chemical compounds) that improved how the body processes fats and amino acids—two key processes in managing diabetes.

When exercise was added to the diet changes in three studies, the benefits appeared to be even stronger. However, the researchers noted an important finding: some of these beneficial changes didn’t last permanently. If people stopped eating healthy or exercising, the bacteria could shift back toward unhealthy patterns. This suggests that maintaining the lifestyle changes is crucial for keeping the benefits.

Beyond just counting bacteria, the studies measured what these bacteria were actually doing in the body. Metabolomic analysis (looking at the chemical products bacteria make) showed that healthy diets led to increased production of short-chain fatty acids, which are like fuel for the cells lining the intestines and help regulate blood sugar. The studies also found that inflammation markers in the blood decreased as the bacteria composition improved. Some studies tracked insulin sensitivity (how well the body responds to insulin), and this improved alongside the bacteria changes. Additionally, the research showed that the specific type of diet mattered—different healthy diets produced somewhat different bacterial changes, but all moved in a beneficial direction.

Previous research has shown that diet and exercise help people with type 2 diabetes, but scientists weren’t sure exactly how. This review adds an important piece to the puzzle by showing that gut bacteria changes are a major part of the explanation. Earlier studies had suggested that gut bacteria might be involved, but this systematic review provides stronger evidence by combining multiple studies. The findings align with other research showing that people with type 2 diabetes often have different gut bacteria than healthy people. This review goes further by showing that lifestyle changes can actually reverse some of these unhealthy bacterial patterns.

The biggest limitation is that the studies combined only included 319 people total, which is a relatively small number. This means the results might not apply equally to everyone, especially different age groups, ethnicities, or people with different types of diabetes. The studies used different types of healthy diets (some emphasized fiber, others focused on different nutrients), making it hard to say which specific diet works best. The studies also measured bacteria in different ways and at different time points, which made comparing them challenging. Most importantly, the studies were relatively short-term, so we don’t know if the bacteria changes and health benefits last for years. Finally, the studies didn’t always clearly explain why some people responded better than others to the same diet and exercise changes.

The Bottom Line

If you have type 2 diabetes or prediabetes, eating a healthy diet rich in fiber and whole foods appears to help by improving your gut bacteria. The evidence suggests moderate confidence in this approach. Adding regular physical activity may provide additional benefits. However, these changes need to be maintained long-term to keep the benefits—stopping the healthy habits may allow the bacteria to shift back to unhealthy patterns. Talk to your doctor or a dietitian about which specific diet approach might work best for you, as different healthy diets may work differently for different people.

This research is most relevant for people with type 2 diabetes or prediabetes who want to understand how lifestyle changes work. It’s also important for people at high risk of developing diabetes. Healthcare providers should use this information to explain to patients why diet and exercise matter beyond just calories. However, this research doesn’t apply to people with type 1 diabetes (a different condition) or those who cannot make dietary changes for medical reasons. If you have severe diabetes complications or other serious health conditions, consult your doctor before making major diet or exercise changes.

Changes in gut bacteria can begin within weeks of starting a healthy diet, but the full benefits for blood sugar control typically take 4-12 weeks to become noticeable. Some people may see improvements faster, while others take longer. The key is consistency—eating healthy most of the time produces better results than occasional healthy eating. If you stop the healthy habits, the bacteria can shift back within weeks, so maintaining the lifestyle changes is essential for long-term benefits.

Want to Apply This Research?

  • Track your daily fiber intake (aim for 25-30 grams) and note any changes in energy levels, digestion, and blood sugar readings over 8-12 weeks. Record which healthy foods you eat most often, as different foods feed different beneficial bacteria.
  • Start by adding one high-fiber food daily (like beans, whole grains, or vegetables) and gradually increase your intake. Pair this with 150 minutes of moderate activity per week. Use the app to log meals and exercise, and set reminders to maintain consistency since the benefits depend on sticking with the changes.
  • Check in monthly on how you’re feeling, your energy levels, and any changes in blood sugar readings if you monitor them. After 3 months, review your consistency with the diet and exercise plan. If benefits plateau, try varying your healthy foods to feed different types of beneficial bacteria, as diversity appears important.

This research summary is for educational purposes only and should not replace professional medical advice. The studies reviewed were of moderate quality with small sample sizes, so results may not apply equally to all people. If you have type 2 diabetes, prediabetes, or any other medical condition, consult your doctor or registered dietitian before making significant changes to your diet or exercise routine. This is especially important if you take diabetes medications, as dietary changes may affect how your medications work. The bacteria changes described in this research are promising but are not a substitute for medical treatment prescribed by your healthcare provider.