Podcast: Diet, physical activity or both for prevention or delay of type 2 diabetes mellitus and its associated complications in people at increased risk

There are concerns across the world about the rising incidence of type 2 diabetes, increasing the importance of evidence for effective ways to prevent this condition. In a December 2017 update to the Cochrane Review, Bianca Hemmingsen from Herlev University Hospital in Denmark and colleagues have summarized the latest evidence on the effects of diet and physical activity for people with intermediate hyperglycaemia or prediabetes. We asked Bianca to tell us what they found in this podcast.

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John: Hello, I'm John Hilton, editor in the Cochrane Editorial and Methods department. There are concerns across the world about the rising incidence of type 2 diabetes, increasing the importance of evidence for effective ways to prevent this condition. In a December 2017 update to the Cochrane Review, Bianca Hemmingsen from Herlev University Hospital in Denmark and colleagues have summarized the latest evidence on the effects of diet and physical activity for people with intermediate hyperglycaemia or prediabetes. We asked Bianca to tell us what they found in this podcast.

Bianca: More and more people are being found to have intermediate hyperglycaemia or prediabetes, due to eating habits and physical activity levels. Although some people with prediabetes will never develop type 2 diabetes, interventional and observational studies have shown a reduction in type 2 diabetes with reduced calorie intake and increased physical activity in people with this diagnosis; and diet plus physical activity is recommended in international guidelines for people with prediabetes.
In this update of our July 2008 Cochrane Review, we investigated whether diet, physical activity or both could prevent or delay type 2 diabetes and its associated complications in people at increased risk. We also looked for evidence on whether these interventions might be associated with serious adverse events, such as traumatic injuries caused by different types and intensities of physical activity.
We searched for randomised trials in which people with intermediate hyperglycaemia were allocated either to an intervention based on diet, physical activity or both; or to a control group with a standard intervention or no diabetes-related intervention.
Our updated review includes 12 trials, with approximately 5200 people. Eleven trials compared diet plus physical activity against standard or no treatment. Two trials compared physical activity with standard treatment and one trial compared a diet-only intervention with a physical-activity intervention or standard treatment. Diet interventions often included reduced calorie and fat intake, while physical activity interventions often included cycling, walking or similar.
We found no firm evidence that diet alone or physical activity alone influences the risk of type 2 diabetes compared to standard treatment. However, diet plus physical activity prevented or delayed the incidence of type 2 diabetes in people with impaired glucose tolerance. There are insufficient data for the effect of diet plus physical activity for people with intermediate hyperglycaemia defined by other glycaemic variables. Likewise, there is not enough data for us to analyze the effects on complications associated with diabetes, socioeconomic status or health related quality of life.
In summary, there is moderate-quality evidence that diet plus physical activity reduces or delays the risk of type 2 diabetes in people with impaired glucose tolerance. But, there is no clear evidence on whether this benefit would be achieved for people with increased risk defined by other glycaemic variables, such as impaired fasting glucose or elevated glycosylated haemoglobin A1c (HbA1c) levels; or on whether diet alone or physical activity has an impact. It remains uncertain whether the reduction in the incidence of type 2 diabetes mellitus with diet plus physical activity in people with impaired glucose tolerance will decrease its long-term complications. This needs to be studied in future trials, which should also investigate the effects in people with impaired fasting glucose or moderately elevated HbA1c, and focus on patient-important outcomes.

John: If you would like to read this current version of the review and watch for further updates should those trials be done, you can find it online, with an internet search for 'cochrane diet and physical activity to prevent diabetes'.

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