Intermittent fasting is a very popular, well promoted diet option these days. Especially for runners. The idea that running fasted will allow your body to use and burn more fat stores to aid in weight loss, increased endurance, and better health.
Except you tried it and it didn’t work for you. You felt worse. You gained weight. You were grumpy and hungry all the time.
So what’s the deal?
And besides the big issue of, you don’t need to lose weight to be a better runner, there are many more issues related to running and intermittent fasting (IF) that can be more harmful than beneficial.
Here’s why I don’t practice intermittent fasting as a runner and why I don’t recommend it to active women.
1. You need breakfast. You need stable blood sugar to have balanced hormones and you cannot have balanced blood sugar without breakfast. You also need breakfast to kickstart your day, your metabolism, and fuel your training well. Eating for your training isn’t just what you eat DURING the run, but what you eat all day, everyday to support your activity and your life.
2. You need to eat enough total calories to fuel your activity. If you are under fueling, you will not be able to build mileage and intensity in your training plan. You also need enough calories to build muscle. And you need strong muscles to support your body’s movements while running. Restricting calories (intentionally or unintentionally) leads to low energy, early fatigue, and poor recovery.
3. You need enough carbohydrates. Carbs are not the enemy. They are your body and brain’s preferred energy source, and they are necessary to fuel high intensity activity.
4. You need to balance your overall stress load. Intermittent fasting is a stress on the body because you are not giving it fuel it needs. Running is a stress on the body because it is a high intensity effort (even easy running!). Add on top of that the everyday stressors of work, family, kids, appointments, LIFE. During a training season where you have a higher load of stress on the body from your activity, you need to reduce the stressors in other areas as best you can to allow your body to adequately recover and be able to handle the next day’s training. If you aren’t giving your body a break somewhere, it will eventually find one for you.
So why does all the research say intermittent fasting is good for you?
Studies on intermittent fasting have been performed on men and non-menstruating women. So they are not taking into account fluctuating hormone responses from a female’s 28 day cycle. The metabolism of the active woman is much more sensitive to dramatic restrictions in intake because our hormones are designed differently. We are the ones who reproduce and carry out the survival of our species. We have physiological differences in how we respond to food availability. Instead of losing fat, fasting causes menstruating women to store it out of natural survival instinct. The cortisol increase from the stress of skipping meals also leads to the storage of more fat. This article goes into more detail on this really well.
Why are all your friends seeing results with intermittent fasting if it isn’t good for you? (And why are they getting results and you aren’t?)
Women who have optimized hormone health, no history of trauma, have built stress resiliency, and have not been fasting for a long time, may see results. Just like any low calorie or restriction diet has initial results The body is in a calorie deficit, so we will see weight loss, maybe fat loss, but also muscle loss. And over time, the body will build up enough prolonged rise in cortisol, that it won’t be able to take the load anymore. That friend who is doing so great with fasting will eventually crash. Because the body cannot sustain it.
If you are wanting to try fasting as a way to lose weight or optimize your hormones or feel more energized or sleep better, you’re probably already in a state of needing MORE nutrition. So giving your body less than it needs will only push you further down the path you’re already on. In order to feel better, have more energy, and reach your fitness goals, you need to fuel your body adequately.
What about the argument that you are eating enough calories during your eating window, so it’s not an issue of not eating enough?
Your body needs fuel at regular intervals, starting with breakfast. Breakfast is the catalyst for the rest of the day. For your metabolism, your circadian rhythm, your hormone health, your sleep at the end of the day. Even if you are eating enough food during your eating window, your body is still in a fasted state for long enough that it is going to store as much as it can and not have the available fuel available to support your day.
Where do you start if you’ve been doing intermittent fasting and want to start fueling your body well?
Eat breakfast. Eat within an hour of waking up, and make sure your plate includes protein, carbs, and fat. (More tips on how to do that HERE!)
And for specific running nutrition tips, grab my Nutrition for Endurance Athletes cheat sheet HERE or in the Free Resource Library.
