Intermittent fasting, diabetes and endurance training: review and updates!

I am a big fan of intermittent fasting. It makes me feel great, it improves my sleep, my digestion, my focus. It improved my insulin sensitivity, blood glucose stability and I consider it a key factor in my 90% time in range challenge - which in turn facilitates weight and body composition control. Most of all, ever since I practiced it my relationship with food has massively improved, which is quite a big deal for a guy with a bottomless stomach. And because those immense portions I ate often slided into uncontrolled overeating that made me feel guilty at times, my mood also improved once my eating window narrowed.

In fact, I think everyone should try some form of time restricted feeding. Its benefits extend much further than mere weight loss, and to me it has turned into a mental gym, a great way to exercise the self-control muscle.

Intermittent fasting is also a great tool to leverage in combination with physical activity. It is a great tool to ease weight loss, just as much as it does not gets in the way of muscle building if one wants to. I personally tested it in both sides of the spectrum, and it worked perfectly: cutting was easier because I just could not stuff that much food in my body in such a small time window (19 hours of fasting to 5 hours of feeding, usually), and bulking was never impeded, since broadening the feeding window was enough to get the extra calories in.

Intermittent fasting and increased training volume: still feasible?

So far so good. Then I started to run again, adding a couple of zone-2 long(ish) runs per week on top of the strength training, and questions started to pop into my head.

One’s life schedule can be very different, and different people will have very different lifestyles. My energy requirements will change substantially if I add running to my strength training, and they will surely be extremely different than those of someone who is moderately, if not active at all.

If a less active individual could experience the benefits of intermittent fasting in terms of weight loss (not forgetting that any long-lasting weight loss and change in body composition MUST involve resistance training), things get murkier for an athlete whose training schedule involves 8-9 workouts per week, mobility training excluded, like me.

These questions got louder in my head after I  listened to this episode of the Trail Runner Nation Podcast, where the guest Coach Bob Seebohar has some interesting points about fasting. Something he said, which I had never considered before, is that all the benefits of intermittent fasting are true, but research about intermittent fasting has been done extensively on sedentary/normal people…not as much on athletes!

Intermittent fasting and recovery

…and this opens a whole universe of doubts and considerations for me. I’ll start my brainstorm from the basics. Physical exertion requires rest and recovery. Workouts are a stressor for the body, which will need some time to adapt to the stress induced and recover from it. For me, recovery typically involves some form of light activity (walking or mobility training and stretching), plenty of sleep and good nutrition.

Good nutrition means whole, plant based, carbohydrates rich food taken from the always great ‘green light foods’ list available on the Mastering Diabetes website. The timing of meals has not been a great concern so far. Working out early in the mornings (plus a lighter session late in the afternoon), with an eating window that ranges between 2pm and 7.30pm approximately never caused any issue in terms of recovery and performance. As long as the food that makes it into the dish is spot on in terms of macro and micronutrients, I am always ready to go.

Then, when the running increased, I started to experience some extra fatigue towards the last few miles of every run, which I typically do right before breaking the fast, i.e. at the end of the 19 hours fasting window. My insulin sensitivity and glucose stability still being great, my performance started to suffer a bit. In the podcast I mentioned earlier the guest points out that it takes up to 24 hours for carbs gas tank/glycogen stores to get replenished and for our body to be able to take the physiological adaptation induced by a work out.

That being the case, my fasting protocol would be consistently getting in the way of performance.

Plus, intermittent fasting (in fact, fasting in general) being a stressor itself, it would be stacking on top the stress induced by physical activity, and if poorly managed it can easily get in the way of proper recovery, mine the performance and cause injuries.

So, if one is intermittent fasting the whole week (like me), the consistent mismatch between the time it takes to replenish the glycogen stores and the body’s needs for it at the start of the workout could impair your performance, especially when the workout frequency increases from once a day to twice a day.

Other potential negative consequences include missing out on several nutrients. If one is not attentive to what ingredients make the meal, there could me micronutrients deficiencies which can lead to issues with bone density, maintenance and recovery.

Micronutrients intake has always been a point of care for me (I stick to the ‘eat the rainbow’ rule…easy!), but this is the first time I am eating this way while training in endurance sports.

Reviewing my approach

So now I am wondering whether or not I will be able to stick with it as my running volume increases.

It is not so much the amount of kilometres that scares me, as much as my ability to run them with the right level of energy, the quality of the recovery process of my body after the run, and it’s readiness for the next workout.

I won’t deny any of my previous statements about intermittent fasting: generally, science on the topic supports that eating less frequently is just great for longevity. Personally, it has greatly improved the management of my type-1 diabetes, making me far less insulin resistant and increasing my time in range up to 95% over months.

But I am now reviewing my own approach. A passage from Tom Delauer’s appearance on the Modern Wisdom podcast, really rang a bell for me.
Around minute 43, he points out that:
“The best form of intermittent fasting is the one that you don't get addicted to, the one that you can still use as an effective tool without using as a crutch. The best form of intermittent fasting for the individual is going to be the one that you feel the best on. The one that you get the heightened mental alertness, that clarity that you seek out. The moment that you start to do it because of an arbitrary number is the moment that you've already lost the battle.”
I realised that probably I am sticking to my 19-5 fasting routine more because I feel good about hitting those “19 hours” of fasting every day than for any other logical reason. In other words, I am keeping at it as is just to feed my pride, potentially undermining my body’s recovery.

Next steps

Given what I have recently learned in the process of writing this post I think I will introduce some changes. In particular now that I will start marathon training, I will make sure I get to train with a full glycogen tank, and that when the run is on top of a strength training workout, I eat right after in order to kickstart the body’s recovery as soon as it needs it.

I will keep my blood glucose and insulin requirements in check throughout the experiment, as per use. But I have no reason to fear any major disruption if I eat Mastering Diabetes recommended ‘green light foods’.

I’ll keep you posted!