An important part of getting fitter, and improving both speed and endurance is training the body to burn fat at higher levels of intensity. This is really important for athletes who do the things I like doing – running (because they can go faster and further) and mountaineering (because mountaineers don’t have very good access to food to top up their limited carbohydrate stores).

One of the advantages of having diabetes is that I can observe how much carbohydrate I need to eat to keep my blood sugar stable. Does this mean that I have an insight into how well my body is adapting to burning fat? Can this help anyone else?

What does my data say about “fat adaption”

I’m currently training for an ultra-marathon in the Brecon Beacons in two weeks time. (Finishing it in fourth place last year was probably the proudest moment of my life, and one which will be very hard to emulate – I now know that I can run ultras with diabetes and run them fast – so what magnitude of challenge do I need to take on to face that level of “unknown” again?) When running with diabetes it is very important to understand how much carbohydrate one must consume to keep blood sugar levels stable. So I keep data on it.

The fact: I need to eat less carbohydrate during long low-intensity exercise than I did a year ago.

For slow steady, prolonged exercise, my requirement to consume carbs has fallen.

For slow steady, prolonged exercise, my requirement to consume carbs has fallen.

Lots of things have changed over the past year. My requirement for long acting insulin has increased. I take twice as much long-acting insulin now than I did last year. The more insulin I take, the more carbs I need to eat during exercise. So it could just be that I don’t take enough long-acting insulin now – even though I take more than I used to. But it seems to be appropriate for my blood sugar generally so I’m not sure if insulin dosage is the culprit.

I was always fit, but compared to last year I have built a huge endurance base: in theory, my body has adapted to burn more fat at higher exercise intensities. This is important for endurance because the body stores a lot more fat than carbohydrate so it prolongs the moment when the carbohydrate stores are fully depleted and the athlete “bonks”.

So does the fact that to maintain stable blood sugar, I need to eat less carbs whilst exercising than I used to mean that I burn more fat and less carbs for energy? (Or does it mean that I will bonk sooner because I’m not replacing carbs at such a high rate?) I think it probably means the former.

Finally, traditional exercise nutrition recommends that an athlete consumes 60-70g of carbs an hour (for my weight). I’m not sure many ultra athletes eat that much, but should I be aiming to eat as much as possible or is it just not necessary? I would love any sports nutritionists who are reading this to give me their opinion.

Before the CCC, I took a bit less long-acting insulin than usual because I was again stepping into the unknown and was afraid of getting a hypo. It turned out that it wasn’t enough and my blood sugar stayed at the top of its safe range for the first seven hours of the race despite me eating less than 5g an hour of carbs on average. I was struggling by half-way (where I took some more insulin and ran the second half eating about 40g an hour) but it was a lesson in how amazing the body is at functioning with almost no additional fuel!

Intense exercise burns more carbs but can also delay the need to eat any

When exercising at high intensity, the body has to rely on the carbohydrate metabolism more. But because of this, the liver dumps some stored carbs into the blood in anticipation. This means that for me, if I sprint, my blood sugar will initially go up. I also find that doing interval training raises my blood sugar – and delays the need to eat – more than doing the same distance and time at a steady pace.

For 70 minutes of exercise covering the same distance, I have different carb needs depending on whether the exercise is in intense bursts or slow and steady

For 70 minutes of exercise covering the same distance, I have different carb needs depending on whether the exercise is in intense bursts or slow and steady

I love burning carbs!!

Since learning about building an aerobic base, I do most of my exercise at a relatively low intensity to optimise that fat burning process. And I’ve seen amazing results at both endurance and speed. But interval and speed training is important too. I love the feeling of having exercised hard – it can come from doing a really intense training session or from running a really long way. I love that tired feeling in my legs. I have no idea about the science, but I can almost feel my body’s craving carbs to replace its depleted glucose stores. When I feel like that, I know that I need to eat a lot of pasta and that I will hardly need any insulin to manage my blood sugar. This heightened sensitivity to insulin following exercise is why exercise is so important for people with type 2 diabetes or insulin insensitivity.

Exercise is surely good for everyone’s blood sugar control

Since getting back into training properly about three weeks ago, my blood sugar upon waking has been between 5 and 6 mmol/litre almost every morning (despite it sometimes being bit haywire at times when going to bed), a level which is basically perfect – well done me! It’s definitely good for my peace of mind to know that I am minimising long term damage to my body by running a lot.

That is why exercise is so important for people with type 2 diabetes or insulin insensitivity.

And apart from all this complicated stuff about blood sugar control, exercise and adventure are just good for the soul. Going back up into the mountains over the past few weeks and running for hours at a time is wonderful. Surrounded by walls of rock, snow, and wild animals, breathing cold air and putting one foot in front of the other, I feel strong (if only fleetingly!) and alive.

At this moment, I didn't give a monkey's about how my fat burning metabolism was going - I was just loving sharing the mountain with these Ibex.

At this moment, I didn’t give a monkey’s about how my fat burning metabolism was going – I was just loving sharing the mountain with these Ibex.

Another day, another Ibex. I will never get bored of meeting these gentle creatures.

Another day, another Ibex. I will never get bored of meeting these gentle creatures.

 

7 comments

  1. Great article! I notice a similar effect on glycemic stability – when I’m training intensive my BGs are much more stable. Have you thought about measuring your respiratory quotient using breath analysis to measure the ratio of fat to carb burn at different intensities? I have done this – it was interesting. Let me know if you’d like the details. Now that i’m on a LCHF (low carb/high fat) diet I will probably do it again to see if it has changed. Also, have you thought about LCHF?

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    1. Thanks. I haven’t done a respiratory test but it sounds interesting. I have done a blood lactate test on a treadmill to find lactic acid levels at various speeds. It was a good way of working out training zones. I’m still not sure about HFLC diets. I would think that my diet is HFLC relative to the traditional advice given to athletes. When I’m active all day I won’t take insulin until the evening which means not many carbs. (I worked out that on a two week skiing holiday last winter I had 900 calories a day of olive oil!) Do you find that you have enough fuel on board for intense workouts on HFLC? how many grams of carbs so you eat per day? I have about 200-300g and as a total guess that is around 30-35% of my calorific intake.

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      1. I haven’t yet trained at high intensity on LCHF – I have spent to past few weeks getting basal reduction and timing right so that if I train at my “all day” pace I can do it without carbs (I drop my basal to zero two hours before exercise, and take it back to normal an hour before I stop). Seems to work fine. I reckon this won’t work at higher intensities without carbs, so I might do a metabolic test to see how intense I can get without carbs and use that as a basis for some more experiments. I eat about 30g CHO/day, which is about 5% of my calorific intake, 10% protein and the rest fat. Will write this up and stick it on my blog sometime!

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  2. Very interesting – cutting out the empty carbs, trying to get in lots of nutrients through real foods and training at low intensities to encourage fat burning and weight loss – all of this enabled me, at 57 years old, to complete a 100kms race. Now, no matter how hard I train, I find it very difficult to reach that stage of total physical tiredness that I think most endurance athletes crave. Is it the diet or is it just physical adaptation to the enormous volume of training and racing I’ve done over the last 2 years? I just don’t know, but I suspect a bit of both, or maybe I’ve just acquired so much mental toughness that I’ve become numb to the discomfort. Great post though.

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    1. Sounds like you’ve had an amazing journey. It’s funny with diet – on the Brecons ultra on Saturday i was talking to a (very fast) vegan. He was saying that his recovery is much better now he’s vegan. With type one, i will never be able to try his diet of 10 bananas for breakfast though! Hope next year’s running goes well for you.

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  3. Alex – great post! I’m pretty much an exercise addict because of the stability brought on because of exercise. If I go more than a day without exercise I feel, and maybe this is in my head, that my control gets poorer.

    One thing I’m still learning is how to go “low and slow” to encourage burning fat. Your experience definitely adds a perspective.

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