Can intermittent fasting lower blood glucose levels?

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Can intermittent fasting lower blood glucose levels? A new study in the Clinical Diabetes and Endocrinology Journal recently set out to answer this very subject.

Intermittent fasting has been around for some time but the mystique surrounding it continues to pop up in our social feeds.

This specific study aimed to see if intermittent fasting can be used to lower blood glucose levels in place of conventional medications.

They did this by looking at the most relevant studies published on the topic using a research method called a review article. Essentially, they looked at various different studies and aimed to see what the overall outcomes are when considered together.

The study looked at people in the United States where there are currently 34.2 million cases of diabetes (2021). This fact shocked me a little bit. Coming from the humble Islands of the United Kingdom , 34.2 million is roughly equivalent to half our entire population in England.

So needless to say, this is a big problem in the US. That said, our best estimates for the UK is there are currently 5 million people living with diabetes. So we also have a pretty serious problem.

Why the study?

Diabetes dramatically increases the risk of you developing complications related to the diabetes. These can be both vascular or non vascular issues. Vascular problems include conditions such as cardiovascular disease, problems with the eyes, problems with the kidneys and events like strokes.

Non vascular on the other hand effect the motility of food in your gastrointestinal tract (delayed gastric emptying), nerve damage, increased risk of infections, problems with your teeth and the list goes on and on.

This is a problem because it has knock on effects to healthcare budgets. Not to mention the effect on the poor patients living with these complications.

Granted, the US has a different model of healthcare, which is an insurance based system. So they pay for their care and so perhaps it’s not such a big issue in terms of government spend.

However, in the UK, diabetes accounts for 10 percent of our national NHS spend. That’s £10 billion per year for cases that can mostly be delayed or avoided completely.

Study rationale

The study also raises an interesting point and rationale for doing the study. They argue type 2 diabetes is caused by insulin resistance in the body. This means your body produces insulin but it doesn’t work very well.

Yet many diabetes treatments focus on increasing the amount of circulating insulin in your body e.g. insulin, sulphonylureas, GLP-1 agonists, and DPP4 inhibitors.

Therefore, the authors argue treating diabetes with multiple therapies that increase the amount of insulin and not the efficiency of insulin in your body is flawed. They also point to evidence that shows people who go onto certain medications, such as insulin, gain more weight and enter a state of having far too much insulin their bodies (hyperinsulinaemia).

As type 2 diabetes is caused in most people by being overweight, medications that make you gain weight are obviously not ideal.

Instead, focusing on lifestyle interventions to help people lose weight and get fitter treats the underlying insulin resistance.

As a comment, there are 2 elements to this logic I do not necessarily agree with. First of all, some of the above medications effect the body in many ways with an increase in insulin production being only one of them. Some medications do also treat the insulin resistance referenced in their logic.

Second, we know from seeing patients regularly that these therapies actually work at reducing blood glucose levels. Third and lastly, relying on patients to make lifestyle changes and thus not choosing to treat them medically, could have health consequences. For the best will in the world, we have enough experience to see most lifestyle change attempts, do not last. However, I am always for lifestyle interventions as first line treatment.

Nonetheless, it is an interesting rationale.

What is intermittent fasting

Can intermittent fasting lower blood glucose levels

We’ve blogged on this topic before (here) but I’ll give you the quick summary. There are lots of different types of intermittent fasting. However, there are 3 main types.

The first is alternate day fasting where you don’t eat or eat dramatically less calories on one day and then eat normally the next day.

The second is time restricted fasting. This means you only eat between certain hours in the day (usually 12pm -6pm but it can vary). Most people do an element of this anyway as most people don’t eat when they’re asleep! So really it only takes skipping breakfast to do this and get the intermittent fasting sticker.

The third way is split day fasting. This is the more conventional type and the one you’ll likely be more familiar with. The most common is the 5:2 method. You eat ‘normally’ 5 days a week and eat only 600-800kcal per day on any 2 days of the week. However, this split can vary.

Proposed benefits of intermittent fasting

When you have type 2 diabetes and are overweight or obese, you normally have high levels of insulin circulating in your body. However, you also have high levels of another hormone called leptin.

Leptin is released from fat cells and helps send signals to your brain to tell it you are full up. Therefore, normally leptin will be at its highest level after eating.

Like insulin, when you’re overweight or obese, you can become leptin resistant. In other words, you don’t feel full. You then need more leptin to get the same message to the brain.

Leptin is also pro inflammatory. It causes inflammation in the body. Therefore, high levels of leptin can cause damage to the body over a long period.

On the flip side of this, you release another hormone from fat cells called adiponectin. Adiponectin kind of works in contrast to leptin. The authors suggest adiponectin encourages increased muscle mass, encourages liver fat breakdown and it is thought to be anti-inflammatory.

So keeping the balance between leptin and adiponectin appears to be important.

Why intermittent fasting is used as the diet of choice?

The authors state there is evidence to show people are more likely to stick with intermittent fasting longer than other diets. By definition then, if you can stick to a diet longer, you will lose more weight and thus lower blood glucose levels even further.

As a result, you reduce the insulin and leptin resistance in your body whilst increasing adiponectin levels. This then encourages more liver fat breakdown and an increased muscle mass production leading to better diabetes control.

The authors call this sequence of events metabolic reprogramming. It sounds quite sexy but essentially they are talking about taking your body from an obese state to a normal healthy state.

So can intermittent fasting lower blood glucose levels? Study results

Before interpreting the results I just want to highlight there are a few problems with this study that we’ll discuss below.

Nonetheless , if we take the findings at face value they are quite promising. When an intermittent fasting group was compared to a control group (a group that carries on as normal), the intermittent fasting group had more weight loss, lower blood glucose levels and greater adiponectin levels.

A different study looked at intermittent fasting compared to continuous calorie restriction. Here a group who ate 1200-1500kcal per day was compared to an intermittent fasting group who ate 500-600kcal 2 days a week. Both groups demonstrated similar reductions in their weight and blood glucose levels.

Another study compared what happens when 2 groups achieve the same average calorie intake using either continuous calorie restriction or intermittent fasting. The continuous group ate 75% of their maintenance calories every day compared to the fasting group who cycled between eating 125% and 25% of their maintenance calories.

Once again the results were very similar amongst the groups.

This is an interesting finding because I bet there will be many people out there who would prefer 2 days of a low calorie intake compared to continuously eating 1200-1500kcal per day. Granted the fast days are more extreme but they are less frequent and therefore might be easier to stick to.

Problems with the study

I said there were some problems with the study and we need to look at this to remain balanced in our analysis.

First of all I was a bit disappointed to find they only looked at 8 studies. It’s a small sample size and therefore it makes it hard to draw definitive conclusions. However, I will sympathise with the authors as I suspect there isn’t an abundance of studies on the topic.

The studies they did look at ranged only between 4-24 weeks. Again, this was disappointing as the authors state intermittent fasting is more sustainable over the long term yet all of the studies referenced are below 6 months in duration.

I’d also question the notion that people can stick to intermittent fasting longer than other diet. This is not a proven fact from the research I have read or from my experience in practice.

Ultimately, research looking at diet always has its problem. I’ve blogged on this previously on my Youtube channel which you can find here. Therefore, it’s always difficult to find definitive answers on such subjects.


Every study I have read on intermittent fasting demonstrates it is an effective tool for weight loss and/or lowering blood glucose levels.

However, despite claims to the contrary, I have yet to find compelling evidence it is any better or more effective than any other dietary method.

Once again, this study supports the notion that intermittent fasting is as good as continuous calorie restriction but no better.

I can certainly see how people could do well with fasting. It gives clear rules and allows a bit more flexibility to peoples diet than possibly continuous calorie restriction might offer. However, the fast days are hard work and so might not be everyone.

If you take medications, particularly for your diabetes, it is worth speaking with your diabetes team or GP/practice nurse before starting a diet. Some diets like intermittent fasting may effect the dose or choice of these medications and therefore need to be considered. This is particularly true with insulin where your glucose levels may vary based on your dietary choices. So if you have low calorie days you might be at risk of low blood glucose levels.

Need more help

If you need more support we offer a range of 1:1 consultancy services and online programmes focused on helping you improve your glucose control and health for the long term. These include our type 2 diabetes recovery programme, type 1 glucose stability programme and winning weight loss programme. Go to the pages using the links above or in the headers or get in touch if you have questions.