How this Dietitian Actually Feels About Fasted Training & Intermittent Fasting
This is an updated blog post about a topic I previously wrote about last May. My stance on this subject has changed since then. I do not recommend fasted training to any of my clients unless they are going for a leisurely walk, but even then…I’d rather you not be starving yourself. Period.
Why did I change my mind about this concept?
There is a plethora of research to support fueled training, much more than there is to support fasted training.
You’ll get more out of any kind of workout if you fuel before, during, & after
Fasted training & intermittent fasting can damage hormones in men & women, which can lead to injury. I actually already knew this since I under-fueled my body as a collegiate athlete. I ended up with bone damage, secondary amenorrhea, & a disordered relationship with food. As a woman in disordered eating recovery, I function better, I perform better - in the mountains & in life - if I do not engage in fasted activities or limit food to a certain window of time.
If you are using intermittent fasting to lose weight as an active individual, be aware that you’ll probably be losing muscle mass as well, which will decrease your metabolic rate…that’s not what you want.
I first heard about the concepts behind fasted training and fat adaptation from the Uphill Athlete community, specifically an episode from the podcast with Rebecca Dent, the sports dietitian on staff for Uphill Athlete. I played a power sport in college (softball), so I’m actually fairly new to endurance training. But now, as a mountain athlete that tries to take advantage of every season where I live, I am involved in activities that require a certain amount of endurance - hiking, mountain biking, and backcountry skiing. I guess I’m an endurance athlete now, so naturally I want to train in a way that will increase my overall endurance for my lifestyle. The number one thing an athlete can do to increase endurance is actually train to increase endurance. Putting in the time to train for endurance is what will promote the body’s ability to adapt fat the most. But training in a fasted state could potentially increase physiological adaptations as well.
Before I break down fasted training and fat adaptation a bit more, I’d like to clarify that I am not discussing or advocating for intermittent fasting for mountain athletes and active individuals. This post is not about weight loss, but rather a training concept that promotes fat as an energy source when glycogen stores have been depleted.
So what is the purpose of fasted training? When should you do it? How can you easily incorporate it into you current training schedule?
WHAT is fasted training? - The body is in a fasted state when it has been unfed for at least 8 hours. Fasted training is a kind of training where exercise is performed without fueling before the activity.
WHY is this kind of training performed? - The theory behind fasted training is that it trains the body to utilize fat as an energy source when the body has depleted its liver glycogen stores. Carbohydrates are the preferred energy source for muscles during endurance exercise, but once the stored form of carbohydrates, glycogen, is depleted from our liver, the body will adapt to utilize fat for energy. This switch from carbohydrate to fat as an energy substrate could be beneficial for long efforts in the mountains when it is not feasible to eat (i.e. when you’re in a “no-fall” zone). But here’s the thing…how often am I in a “no fall” zone? Not often. I’m a leisure mountain athlete, I fuel early, I fuel often, & I have changed my mind about this kind of training because it is based on a theory.
In my head, I am doing my best to put off the dreaded mental “bonk” that comes from a depletion of glycogen and lack of carbohydrates being provided to my brain while I’m being active. The easiest way to do this is to fuel our bodies & our minds. Not to be in a fasted state if possible.
WHEN is this kind of training appropriate? - This kind of training is only recommended for low intensity exercise, like a leisurely morning walk or low grade hike. I do not do this kind of training anymore.
The greater the intensity of exercise, the greater the reliance of your muscles on carbohydrates to fuel the movement. Therefore, it is important to eat carbohydrates around your high-intensity sessions (e.g., strength training, intervals, HIIT) to get the most out of that training.
HOW to perform fasted training? - The easiest way to train in a fasted state is in the morning since the body is in a fasted state from the night before. If this kind of training is not feasible in the morning, a fasted session can be performed if you haven’t eaten for 4-6 hours. Again, I only recommend performing low intensity exercise in a fasted state.
If you’d like to read more about fasted training and how to implement it, here are some helpful articles to get you started:
Nutrition and Fat Adaptation - Uphill Athlete
Nutrition Strategies to Maximize Fat Adaptation - Uphill Athlete
Should You Be Doing Fasted Workouts? - Eleat Sports Nutrition
After training this way for a few months last fall, I noticed that I felt less fatigued during my longer weekend hikes in Grand Teton National Park. I’m excited to see how I feel throughout the upcoming summer months, and I am anticipating that my base level of endurance will be better than it was at the beginning of last summer.
Should you be including fasted training sessions into your current training routine? Like most of my answers related to questions like this, it depends! It depends on so many factors including your current level of fitness, your health goals, your sleep quality, etc. If you’re curious to learn more about how and why I started doing fasted training, send me an email or schedule a quick call to chat about it!
Disclaimer: I am not a personal trainer, just an active individual who likes being outside. If you are curious about starting a new training routine or implementing fasted training into your current routine, I am more than happy to recommend a handful of trainers within the Jackson community to help you get started!
