Diabetes and gut health

By Dr Emily Porter

Dr Megan Rossi in a lab looking through a microscope

What is diabetes?

Over 400 million people worldwide have been diagnosed with diabetes, with most of them having Type 2 diabetes. Type 1 diabetes is an autoimmune condition, whereas Type 2 diabetes (T2DM) is strongly linked to diet and lifestyle choices, alongside other risk factors such as age, genetics and ethnicity.

When we eat foods that contain carbohydrates, these are broken down into smaller sugar (glucose) molecules which are released into the blood. Think of the cells in our body as having a locked door, which requires a key to unlock them! Our cells need glucose for energy so glucose molecules must pass through the door, which is unlocked by the key (insulin).

If the lock is a bit rusty and not responding to the key (insulin resistance) or there are fewer keys (decreased insulin production), then glucose can’t be taken up by cells and stays in the blood, elevating our blood sugar levels. Once blood sugar levels reach a certain threshold, this is diagnosed as T2DM.

How is it managed?

T2DM is often managed with a combination of medications and lifestyle changes, and reviewing diet and activity levels can often be enough to avoid starting medications as they help to improve insulin sensitivity (so the keys can work better!).

For example, higher cortisol levels due to poor sleep or stress, are associated with an increased risk of T2DM. This is because cortisol promotes the production of more glucose by the body, as well as decreasing uptake by cells.

(More recently, there has been a rise in the use of medications, such as GLP-1 agonists, for obesity and T2DM. We’ll cover these in more detail in a future blog post.)

Diet and Type 2 diabetes

There are lots of suggested diet changes for T2DM, including low calorie diets, low carb diets and intermittent fasting (read our blog on this here).

We often see people in clinic who have cut out food groups such as fruit, due to concerns over the sugar content. But the benefits far outweigh the risks of consuming of these naturally occurring sugars; fruit will provide many more vitamins, minerals, fibre and helpful plant compounds (phytonutrients) than a diet snack bar, for example, so it is fine to keep eating fruit in moderation. In fact, we would strongly recommend it!

Opt for one portion at a time and consider adding a protein and fat source such as live yoghurt or unsalted nuts to help regulate the speed at which glucose is released into the blood.

As carbohydrates have the biggest impact on blood sugars, we often focus on the amount and type of carbohydrates in the diet. Whilst lower carbohydrate diets have been shown to help manage T2DM, we want to ensure that we aren’t excluding any of the benefits of carbs such as their fibre content.

How does fibre help our blood sugar levels?

Higher fibre foods take longer to digest, meaning that there is a slower release of glucose molecules into the bloodstream. Due to this, they also help keep us full, meaning they can also help prevent overeating, as managing weight can be one way to improve T2DM.

Research looking at the results of 44 studies showed that people who had more fibre in their diet had better control of their blood sugar levels and reduced risk factors for cardiovascular disease, such as cholesterol levels and body weight.

In the UK, average fibre intake is around 18g (of a recommended 30g per day). The above study advised that people with Type 1, 2 or prediabetes see benefits after increasing from 15g to 35g fibre per day.

As we already know, our gut microbiome LOVES fibre. But how does this fit into T2DM?

What does gut health have to do with Type 2 diabetes?

Scientists have looked at the gut microbiomes of people with and without T2DM and found that they look very different, with decreased diversity and higher numbers of less helpful bacteria in T2DM. Whilst we don’t necessarily know whether this is cause or effect, we know for certain that our gut microbiome plays a role in regulating glucose metabolism. In addition, bacteria impacts hunger hormones, helping to regulate appetite.

We are also learning about how the gut microbiome could be used to predict responses to medications or diet changes for different individuals. In time, this might mean we are able to advise certain diet patterns to people based on their gut microbiome, but we still have a long way to go!

Top 5 tips for eating for metabolic health

  1. Keepskins on fruit and veg to boost their fibre content
  2. Include more beansand pulses in your diet. There is some great evidence for their benefit on blood sugar levels for that meal and even into the next day.
  3. Review your eating window (the time between the first and last things you eat through the day); shortening this by even a couple of hours can be helpful for metabolic and digestive health. I recommend finishing eating slightly earlier as insulin sensitivity is better earlier in the day.
  4. Include fermented foods if you can; fermented dairy in particular may have beneficial impacts on glycaemic control
  5. Spend time in nature, as science has shown a link between green space exposure and risk of T2DM and obesity
An illustration of a person next to a shopping basket full of vegetables


Whilst reviewing the quantity and quality of carbohydrates can be a helpful tool in managing T2DM, make sure to keep plenty of plant-based foods in your diet to optimise gut health too.

Other factors such as poor sleep, stress and smoking have negative impacts on the gut microbiome, which in turn may impact metabolic processes within the body, so always take a holistic approach to your health.

As always, there is no one size fits all, so book in with one of our specialist dietitians who will be able to explore the best ways to manage blood sugar levels and build a personalised plan that suits you.

This article was authored by Dr Emily Porter (PhD, RD)), a gut & chronic conditions specialist dietitian. Do you need support with a symptom, condition or goal? You can book an appointment with Dr Emily Porter or any member of our specialist team here.


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