What actually prevents type 2 diabetes? A review of 378 trials

Your HbA1c came back a little higher than last time. It’s not in the diabetes range, but it has gone up.

So what actually helps, and how much can exercise do?

What the study looked at

Researchers combined 378 randomised trials involving 113,122 adults with prediabetes.

Prediabetes means blood sugar is higher than normal, but not yet in the range used to diagnose type 2 diabetes. HbA1c gives us an idea of your average blood sugar over the previous two to three months.

The researchers compared different approaches, including medication, supplements, lifestyle changes and exercise.

Because many of the treatments had not been directly compared with each other, they used a method called a network meta-analysis. This allows researchers to compare several treatments using the trials that are available. It is useful, but some of the comparisons are indirect.

What did they find?

The biggest reduction in new cases of type 2 diabetes was seen with dual incretin drugs, which are prescription injections that act on GLP-1 and GIP. The risk was around 90% lower than in the control groups.

GLP-1 drugs alone came next, with around a 74% lower risk. Metformin combined with an intensive lifestyle programme was also close behind.

When the researchers looked specifically at HbA1c after one year, the results were a little different.

Only four approaches reduced HbA1c by more than 0.3 percentage points:

* Curcumin * Dual incretin drugs * GLP-1 drugs * Physical activity

Exercise was also one of the most effective approaches for lowering fasting blood glucose after one year.

What does this mean for you?

The interesting part for me is that **exercise was right up there with the medications when it came to HbA1c and fasting glucose.**

It was the only non-drug, non-supplement intervention to achieve a reduction of more than 0.3 percentage points in HbA1c at one year.

That doesn’t mean exercise will have the same effect for everyone. But if your HbA1c is starting to creep up, regular physical activity is one of the first things worth looking at.

The incretin drugs had the biggest effect on preventing progression to type 2 diabetes in this analysis. They are prescription medicines, though, and whether they are appropriate depends on your own blood results, health history and circumstances. This study is not a reason to start, stop or change medication without speaking to your doctor.

Metformin also appeared to work particularly well when combined with an intensive lifestyle programme. In other words, medication and lifestyle were not really competing approaches.

Curcumin and zinc appeared in some of the individual blood sugar outcomes, but that doesn't mean they are proven diabetes-prevention treatments. I wouldn't make a decision about supplements based on one ranking from one study.

And there are some important limitations

This is a very large analysis, but the results still need to be interpreted carefully.

The trials involved different people, doses and treatment periods, and some comparisons were based on relatively small numbers of studies. A reduction in HbA1c after one year also doesn't tell us what will happen over the next 10 years.

The study can tell us what tended to work across the groups studied. It can't tell us which approach is right for one particular person.

If your HbA1c or fasting glucose is starting to drift upwards, that's when it becomes useful to look at the bigger picture — your diet, activity, sleep, weight, stress and other blood markers — rather than focusing on one number alone.

Source: Maria B et al. *Evidence-based ranking of diabetes prevention in prediabetes: A comprehensive network meta-analysis of 378 randomised controlled trials.* Clinical and Translational Medicine, 2026. [PubMed](pubmed.ncbi.nlm.nih.gov/42711998)