Deconstructing the myths surrounding a Low Carb diet and Type 1 diabetes – why it’s another useful tool

Deconstructing the myths surrounding a Low Carb diet and Type 1 diabetes – why it’s another useful tool
Deconstructing the myths surrounding a Low Carb diet and Type 1 diabetes – why it’s another useful tool

Following a discussion on Twitter with someone regarding why a ketogenic diet is or is not dangerous for T1 diabetics, and seeing the usual recurrence of a number of myths that are regularly regurgitated, I thought it would be a good idea to have a look at these and understand what they really mean in the context of T1. Then at least, if people with diabetes know the myths they can at least make their own mind up as to whether they want to consider reducing the carbs in their diet. I realise that this is an often controversial topic, so hang on to your hats.

I thought it would be worth going into these and re-addressing them, as in the majority of cases, they simply aren’t true.

For full disclosure, I typically eat in a relatively low carb way – which for me is less than 80g of carbs a day. When I’m trying to lose weight it drops down to around 30g. That doesn’t mean I do it all the time, but through trial and error I’ve found that it gives me far better blood glucose management and significantly reduces the amount of variance I see in my levels, so I figure that it’s better than the roller coaster which often ensues when I eat more carbs.

Coming back to the myths of type 1 diabetes and low carbs, where do we start? Well let’s look back at a bit of “diabetes diet” history. Pre-insulin, you were basically starved and the main aim of the diet was to stave off diabetic ketoacidosis. In the 1920s to 1950s, the recommended diet was to keep carbohydrates below 75g per day. Why? Because carbs have the largest impact on blood glucose, so with fewer of them in the diet, then there was less likelihood of prolonged high blood glucose levels.

In the 1950s, the American Diabetes Association came up with the Exchanges of carbohydrate model and it all changed. Carbs were on the menu and being eaten once more. Over the next few decades, fat became the evil wrongdoer of diet as Cholesterol (wrongly) became demonized, adding more fuel to carb cult.

We should bear in mind in this context that diabetes blood glucose levels were still mostly recognised as being driven by carb intake.

And then somewhere in this mix research became mixed with chinese whispers to produce some interesting points of view. So what are the myths, where did they come from, and what’s the reality?

Myth 1: Eating less than 140g of carbs per day is dangerous for type 1 diabetics

I’m not sure when this started being communicated in Diabetes training courses, but I am sure of the origins of the idea that 140g of carbs is the minimum required to be eaten every day. It stems from research done by Cahill et al in 1968 that suggests that for the brain to run exclusively on glucose, it requires between 110g and 140g of glucose per day. This book details the studies where this value was determined.

Okay – we have the origin of the 140g – but note that this is glucose and what the brain requires if running exclusively on glucose. It doesn’t say that we need to eat 140g of carbs.

Further research looking at the brain’s use of fuel sources identified that the brain uses lactate when undergoing strenuous exercise ( and on page 277 of this document the following statement is made:

In individuals fully adapted to starvation [or low carbohydrate diets], ketoacid oxidation can account for approximately 80 percent of the brain’s energy requirements (Cahill et al., 1973). Thus, only 22 to 28 g/d of glucose are required to fuel the brain. This is similar to the total glucose oxidation rate integrated over 24 hours determined by isotope-dilution studies in these starving individuals (Carlson et al., 1994; Owen et al., 1998).

Or in other words, when not running on a glucose metabolism, the brain requires less than 30g of carbs and can be 80% fuelled from ketones.

The human body is perfectly capable of creating less than 30g of glucose a day through gluconeogenesis, so will destroy muscle if there is not enough protein or carbs free to feed the brain.

If a T1 eats 140g of carbs per day, they will need (based on a standard insulin:carb ratio of 1u:10g) 14 units of insulin. If they eat 50g, they will need 5u. Eating a smaller amount of carbohydrate that requires less insulin provides much less likelihood of estimation error, or inconsistent insulin absorption.

But the key thing is that you don’t need glucose to provide energy. You can get it other ways, but that’s the next myth…!

What this adds up to is that a human does not need 140g of carbs per day to feed the brain, to be healthy, or to be a safe T1. If anything, it suggests that you don’t need more than 30g and that eating fewer carbs is more likely to be safer!

Myth 2 – Ketosis is dangerous for Type 1 diabetics

Let’s be completely clear on this one. Ketosis, or using fat as a primary fuel source, is a perfectly normal metabolic process. It works extremely well to provide energy when the glucose metabolism is unable to function. When the body works in ketosis, blood ketone levels are typically in the range of 1-3mmol/l. Volek and Phinney have spent a lot of time and done a lot of research on this topic and their work is well established. Most people will actually enter a state where the body burns fats while they sleep!

Ketones are simply the result of the body using fat as a primary fuel source and not a dangerous side product of diabetes that only occurs in diabetics. In combination with blood glucose levels, however, they can be used as an indicator of….

Diabetic Ketoacidosis, where a lack of insulin leads to high blood glucose levels and high levels of blood ketones (typically above about 6 mmol/l), which is not the same. At these excess levels of ketones, the blood pH changes, hence the name.  This is not Ketosis and Ketosis does not lead to this.

The reasons for this confusion must be driven by lack of understanding of the two things and similarity between the terms.

The following picture (courtesy of the aforementioned Phinney) describes the spectrum of ketones in the blood:

The body using fat as the primary energy source results in ketones, but they are not dangerous, even for a T1. They are a normal part of the body’s functioning. Don’t let anyone tell you otherwise!

Myth 3 – You need to eat carbohydrate to get enough fibre and other vitamins to be healthy

Another odd statement that does the rounds. And a lot of care needs to be addressed with this one. Much of the carbohydrate eaten in the western world has very little nutritional value. Sugar, especially, having little to no nutritional value. But what of the key fibre sources? Those such as the favourites in grains, fruit and berries?

Well, yes they are fibre sources that contain a many vitamins and also significant carbohydrate, but you don’t need to eat fruit to get access to vitamins, and until relatively recently, getting fruit all year round was nigh on impossible. Green veg, however was easier, Green veg is perfectly capable of providing the vitamins that can also be gained from fruit. It is also equally effective at providing fibre, but at a much lower carb level.

What about those grains? Per 100g, oats in their wholegrain form have 11g of fibre, 7g of fat, 17g of protein and 66g of carbohydrate. With almonds, the same 100g gets you 12g of fibre, 49g of fat, 21g of protein and 22g of carbohydrate.

There is no requirement to eat foods high in carbohydrate to obtain either fibre or vitamins. Just because our processed diet has evolved that way, mainly through cost considerations, doesn’t make it true.

Myth 4 – You can’t undertake exercise while undertaking a low carb diet

The belief is that without glucose to fuel you, exercise is not possible on a low carbohydrate diet. And yet it’s a commonly done thing. Many body builders do it regularly, and yes, Volek and Phinney have written a book about athletic performance when using a low carb diet.

While certain athletic activities may be slightly more difficult when eating low carb, there’s absolutely no reason not to exercise when low carb. In many activities, e.g. endurance sports, it is a benefit to not rely on glucose. Remember how marathon runners are known to hit the wall? That’s the point at which there is no more glucose to power the muscles. If you aren’t using glucose, why would you hit the wall?

In short, exercise is clearly possible when undertaking a low carb diet, and is to be encouraged. The question is not whether it is possible, but what the impact is on overall performance. As T1s are encouraged to exercise, this won’t stop you.

Myth 5 – Eating a low carb diet dangerously increases your blood lipids

The story goes that if you eat more saturated fat then you end up with high cholesterol. Well, it used to. This report (and many others) beg to differ. Indeed, blood lipids are far more dependent on what your liver chucks into your bloodstream than what you absorb from your diet. In fact, high triglycerides (the key danger element of blood lipids) are mostly created in the liver as a result of high levels of carbohydrate in the diet. We’ve known about this since at least the 1960s but thanks to Ancel Keys, that has mostly been ignored.

More recent research suggests that a low carbohydrate diet actually improves blood lipids. This list includes some of the studies that have shown the beneficial changes to blood lipid results.

What the research seems to show is that far from being the cause of high cholesterol levels, low carb diets improve the risk factors relating to blood cholesterol.

A low carbohydrate diet reduces the markers for blood lipids that have been associated with cardio vascular disease. This is of huge benefit to T1Ds. Fat is not the enemy!

In Summary

In this brief piece, I’ve sought to explain the statements that I regularly see put across as reasons why a T1 shouldn’t eat low carb. Personally I think they are simply brainwashing as a result of the now discredited work that Ancel Keys and others did which have been perpetuated through bad science and poor education (even at higher education levels).

As some foresighted Diabetes professionals have said, they aren’t bothered what an individual eats, as long as they have the right education, tools and help to guide the insulin requirement. And I think that’s what this comes down to.

The usual advice when suggesting something different is not to embark on it without speaking to a healthcare professional. By all means go ahead and do this, but be aware that you may well receive a very negative reaction. Just remember that eating fewer carbs requires less insulin and make sure you dose adjust appropriately.

As a Type 1, you don’t need to eat a low carb diet. It’s not a requirement to keep you alive under normal circumstances. Many of us who generally follow one find it brings better consistency to our blood glucose levels and reduces the incidence and severity of hypoglycaemia. Children would also need careful consideration to ensure they are getting enough calories to grow effectively.

If you struggle with blood glucose roller coasters and high Hba1Cs, it’s another tool in your box that can help you to manage your condition more effectively. Fundamentally that’s what we all need. Tools that make living with the condition easier.

All in all, I wouldn’t say that anyone must undertake a low carbohydrate diet. I’d simply suggest that you might be surprised at the results…


  1. Awesome post! As far as I have read, I agree with everything (and I am reading a lot), specially with your conclusions “it´s another tool”. Sure I will try to reduce our high carbohydrate diet in a healthy way (if I am able, not easy).
    By the way I´m just curious if you still do it, with Openaps and Fiasp (we are on Loop IOs app, looking forward for Fiasp in Spain…). I find it very difficult to get all the calories, everything in the supermarket seems to be high carbohydrate food, and for a child is even more difficult to make it tasty (it needs more time I guess, I don´t like cooking…yet)
    And how do you count calories? Foodmeter app? Thanks again

    • Hi Andrés, I use OpenAPS with Fiasp as a permanent feature of my diabetes management. It works very well when I am both low and high carb. The only real difference is that when I am low carb, if I meal announce, I don’t need to do any bolusing. It all gets managed for me.

      Sometimes you have to get creative, but meats, avocados, nuts, vegetables, oils and such all help with making a fairly low carb diet that can have a ton of calories in it. But then, as you rightly guess, we tend to prepare meals at the weekend and then freeze or refrigerate them for ease of access.

      Calorie counting has all been done through which we’ve found to be much better than many systems, as much of the data is properly curated meaning it’s usually pretty accurate.

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