In this blog for our Evidence for Everyday Health Choices series, Dr Catriona Hilton looks at prediabetes and the evidence on whether diet and exercise can reduce your risk of developing type 2 diabetes.
Most of us will be aware that our modern world has a problem with diabetes, and that it’s getting worse. In type 2 diabetes the body becomes unable to control blood sugar levels, leading to a smorgasbord of complications that can affect almost every part of the body. Usefully, blood tests can detect the stage before full blown diabetes develops, when the body is just starting to have trouble suppressing blood sugar levels. We will call this ‘prediabetes’.
Help! My doctor says I have prediabetes. What now?
First of all, having prediabetes does not mean that you will definitely get diabetes. In fact, fewer than half of people with prediabetes will develop type 2 diabetes within a decade. So, what can you do to avoid it?
As our society has become more overweight and sedentary the prevalence of type 2 diabetes has skyrocketed. Surely it’s obvious then that weight loss and exercise can prevent diabetes? Well, perhaps not. People with prediabetes are currently advised to lose weight and get moving, but the evidence for this isn’t clear cut.
This recent Cochrane Review tried to clarify whether diet, physical activity or both combined can stop (or at least delay) people with prediabetes developing type 2 diabetes.
The authors looking for evidence found 12 randomised control trials that tried to change people’s lifestyles for at least 2 years (and for up to 6 years). Together these studies included more than 5,000 people with prediabetes. The studies were all slightly different but they all allocated people with prediabetes to various interventions of diet and exercise (or continuing as usual) in different combinations.
Eating well and exercising sounds like hard work. Will they stop me getting type 2 diabetes?
The main findings from the review were that:
People who have prediabetes can probably prevent or delay the development of type 2 diabetes by changing their eating habits and increasing physical activity.
It isn’t clear whether diet or increased physical activity alone are effective.
It is uncertain whether diet and exercise affect the risk of heart disease, stroke or death in people with prediabetes. The studies included in the review didn’t mention other complications of diabetes such as kidney and eye disease.
So what does that really mean?
People with prediabetes are currently advised to reduce their calorie intake and increase their physical activity. There is fairly good evidence from this review that this will help to prevent (or delay) the development of full blown type 2 diabetes. It won’t work for everyone though. In the group that the researchers targeted to lose weight and become more active 15 out of every 100 people got diabetes over the follow up period of the studies. In the ‘keep calm and carry on’ group 26 out of every 100 people with prediabetes went on to develop type 2 diabetes. So, you can probably make it less likely that you’ll end up with type 2 diabetes by embracing clean living, but you might still be unlucky.
It might be that changing eating habits or activity levels alone are also effective, but the number of people included in these studies was small, so it wasn’t possible to work out if any effect was real or due to the play of chance.
So, what did the people in the studies actually do? Well, that’s tricky. All the studies included in the review wanted to answer a similar question, but they all tried to do it in slightly different ways. Most dietary treatments aimed to get people to reduce their calorie intakes with the aim of losing various amounts of weight. Some studies also asked people to reduce their fat intake and increase dietary fibre. The exercise interventions also varied. Some studies required people to exercise more intensely, or for more minutes a week, than others.
Patients and researchers may have different priorities
Patients and researchers often have different questions. There are some things that matter to people with prediabetes that weren’t covered that well by the studies.
There are lots of reasons why people want to avoid getting diabetes. Because of the label, because they don’t want to have to take tablets or injections, because of the other health problems that go along with it. The studies included in this review didn’t make it clear whether changing diet and physical activity levels will affect how likely people are to get complications of diabetes (such as foot, eye or kidney problems) or to die. There wasn’t good evidence for a difference in how likely people were to have heart attacks or strokes.
Anyone who’s tried to eat less and move more will know that it’s hard and it requires a bit of sacrifice. It wasn’t clear from these studies whether the people who changed their lifestyles ended up with a better quality of life than those who did nothing.
Where does this leave us?
At the end of the day, we all know that we should chose an apple over a double chocolate cookie and an evening jog over a scandi noir box set on the sofa, but in reality making healthier lifestyle choices is often easier said than done. Most of the studies included in this review used some form of contact sessions to motivate people to change their lifestyles. This just isn’t available to most of us in the real world. We still have a lot to learn how best to support and motivate people to eat well and move more.
On a positive note, there is plenty of evidence that eating a healthy balanced diet and being physically active helps people to live longer and protects against lots of other diseases, so perhaps it’s not a bad idea to give it a go anyway.
Catriona Hilton has nothing to disclose.
Diet, physical activity or both for prevention or delay of type 2 diabetes mellitus and its associated complications in people at increased risk of developing type 2 diabetes mellitus. Cochrane Database of Systematic Reviews 2017, Issue 12. Art. No.: CD003054. DOI: 10.1002/14651858.CD003054.pub4., , , , , .