Prediabetes, diet and lifestyle

by Dr Sue Kenneally

‘Prediabetes’ is the term used for when someone has modestly raised blood sugar levels, higher than the healthy range, but not high enough to be in the diabetic range. Identifying people in this situation is important because if we know about it at this stage before progression on to develop diabetes itself, there is a lot that we can do to prevent this. The two most common forms of diabetes are type 1 and type 2. Type 1 diabetes is a condition where there is little, or no insulin production and people need insulin therapy to maintain their blood sugars in the healthy range. In type 2 diabetes, people still make insulin, but it doesn’t work as effectively as it should. People with prediabetes are at risk of type 2 diabetes, so in this article ‘diabetes’ refers to type 2 diabetes.

A lot of people who have prediabetes will never go on to develop diabetes, but many do, and taking preventative measures at this point is a lot easier than treating or reversing diabetes once it is present. Although reversing type 2 diabetes is possible for most people with the condition, the adage that ‘prevention is better than cure’ definitely holds true here. Diabetes is associated with several long-term complications and increased risk of other conditions including high blood pressure, kidney disease and cardiovascular disease and usually requires multiple medications and constant monitoring to minimise the harm that it can do. 

Diagnosing prediabetes

The usual way to diagnose prediabetes in the UK is to measure the level of glycated haemoglobin in the blood. Glycated simply means ‘joined to glucose’. Haemoglobin is a protein found in red blood cells, and the more sugar there is in the blood, the more haemoglobin proteins become glycated. This is a fairly accurate reflection of how much sugar has been present in the blood in the last three months, and in the UK, it is measures in mmol/mol. Don’t worry about the details of this, but it’s worth mentioning as other countries measure it differently so other articles may use very different numbers. The abbreviation used for glycated haemoglobin is HbA1c. A healthy HbA1c is below 42, while the prediabetic range is 42-47, and anyone with an HbA1c of 48 or more is deemed to be diabetic.

Prediabetes and lifestyle

The two main things someone can do to prevent prediabetes from progressing to diabetes is to focus on their diet and exercise habits. Many people with prediabetes are also overweight as the two conditions are strongly linked. If someone is living with extra weight as well as prediabetes then they should concentrate their efforts on weight loss, as any healthful lifestyle change that results in weight loss should also improve prediabetes. But regardless of body weight, prediabetes can usually be improved with diet and exercise.

Prediabetes and diet

Several clinical trials have assessed different diets and their effects on prediabetes. A recent review identified some recurring themes, and the two with the strongest evidence for improving prediabetes were low calorie diets and low glycaemic index diets. This is great news if you’re thinking of adopting a whole food plant-based diet (i.e., a healthy vegan diet) because this type of diet is both naturally low in calories and low glycaemic index. 

The glycaemic index is a measure of how much any particular food makes your blood sugar rise. A high glycaemic index food or meal will cause it to shoot up rapidly to a high level while a low glycaemic index alternative will result in a slower, lesser increase in blood sugar and this is generally considered to be a more healthful dietary pattern for many reasons, not least because it improves prediabetes.

Whole food plant-based diets are naturally lower in calories than other eating patterns because plants contain fibre and water that keep us feeling fuller for longer and have a low energy density which means that they have fewer calories per mouthful than animal-based foods, so it takes fewer calories to fill us up. All whole plant foods are typically low glycaemic index. 

So, what should I eat?

It’s relatively straightforward; any fruits, vegetables, whole grains, beans and other legumes form part of a healthful diet for prediabetes. Fruit gets a bad reputation because it contains sugar, but the naturally occurring sugars in fruit along with the fibre and water mean that fruit is healthful. When it comes to carbohydrates, try to choose low glycaemic index versions where possible, so for example wholegrain bread and rice rather than white options, sweet potatoes rather than white potatoes, and limit baked goods and refined sugars as much as possible. Nuts and seeds are fine too; they do contain more calories than previously mentioned foods but have a low glycaemic index, so enjoy them in moderation, but as part of an overall varied healthful diet they are very welcome, and a good source of healthy fat.

Should I exercise?

Yes! Exercise helps to regulate weight and has effects on our physiology behind the scenes that act to improve prediabetes even if we aren’t living with a higher body weight. Studies show that people who work on their diet and increase their physical activity levels at the same time get the best results with prediabetes. It doesn’t really matter what you do, find some form of physical activity you enjoy and get moving!


  1. Guide to diabetes (

  2. Yau JW, Thor SM, Ramadas A. Nutritional Strategies in Prediabetes: A Scoping Review of Recent Evidence. Nutrients. 2020;12(10):2990. Published 2020 Sep 29. doi:10.3390/nu12102990