Fasted Running - will running fasted make you faster?

Just because you can run fasted doesn’t mean you should. 

The ongoing debate "to fast or not to fast" sparks passionate discussions within the running community, with proponents highlighting benefits like improved fat adaptation and weight loss, while opponents raise concerns about performance, health, and weight gain. Pro ultrarunner @kilianjornet has publicly discussed occasional use of fasting before easy, low-intensity runs to understand how his body adapts to running with depleted glycogen (carb) stores. Meanwhile, other elite ultrarunners, like @mountainroche attribute the “high carb revolution” as the primary catalyst for the increasing rate at which endurance running records are being broken.

So, what’s the real story behind fasted running, and is it a strategy worth considering for your training? Check out my full article at HERE.

The misuse of fasted training

The line separating fasted workouts from disordered eating can become blurry for athletes.

Proponents claim that fasted workouts have several significant health and performance benefits. The main reasons why athletes perform fasted training include:

• Increasing the rate in which your muscles use fat for fuel 
• Sparing glycogen stores  
• Increasing mitochondrial density

Fat oxidation refers to the process of breaking down fatty acids. To oxidize fat, you need: 

• Healthy mitochondria (the powerhouse of cells where chemical energy is generated to power the cell's biochemical reactions). 
• Fat molecules (specifically triglycerides) to be broken down into glycerol and fatty acids. Fatty acids are then transported to cells and undergo a series of reactions (beta-oxidation) to produce acetyl-CoA to enter the citric acid cycle to generate energy.
• Oxygen (transported to the muscles by blood). Fat cannot be burned (or oxidized) without the presence of oxygen. 

While there are studies supporting the benefits of fasted training, what may start out as a genuine attempt to become more "metabolically efficient" can become a slippery slope that descends into disordered eating patterns. 

Although working out in a fasted state is not an eating disorder, it can be considered a form of disordered eating. This is because any type of rigid food rule about when you can eat may foster unhealthy behaviors around food and may bring on a hyperfixation on body composition. Telling yourself when you can and cannot eat is telling your body that the cues and signals given from the body aren't important and can be ignored. 

Fasted training may seem like an easy option to improve fat burning potential but if you are working out on an empty stomach in order to improve metabolic efficiency, consider the following when it comes to proper implementation: 

• Fasted training is shifting the eating window an hour or two later in the morning while still maintaining proper energy intake throughout the day to support energy and health needs. 
• Proper refueling is key after a fasted session. Failure to adequately refuel will have harmful effects on health and physiological adaptations. 
• The process of fat burning has several components and regulatory mechanisms. A critical component of fat oxidation is oxygen. Fasted training should only be used during low-intensity, "aerobic" training sessions. 
• Fasted workouts should only be done once or twice a week. When there are limited hours between training sessions to refuel and restore muscle glycogen levels, fasted workouts may impair recovery and workout quality may be compromised.
• The ideal phase of fasted workouts is in the early base period when workouts are of low intensity and low volume. 

Fasted workout reminders......

• Weight loss and body composition changes are not goals of fasted training.
• Only one or two low-intensity, low volume sessions per week should be in the fasted state. 
• You can't see or feel the fat that you use for exercise. Fasted workouts are not designed to specifically change how you look. 
• High intensity and high volume workouts should not be done in a fasted state. 
• Athletes should be cautious with fasted training, especially females. Negative effects include elevated cortisol, potential to break down lean muscle for fuel, slow recovery, increased adipose fat, and hormonal issues. 
• Fasted training doesn't work for everyone.  
• Fasted training should not be performed by individuals who have a history of disordered eating or an eating disorder. 

Fasted training for performance is not.......

• Fasting even when feeling low in energy, weak, lightheaded or hungry. 
• Carrying out all weekday training sessions fasted. 
• Increasing workout volume and intensity in a fasted state in order to burn more calories/body fat. 
• Testing how long or hard you can workout before you need to fuel. 
• Using fasted workouts as an excuse to skip a meal or snack. 
• Carrying out fasted training because you think it will help you lose weight.
• Fasting due to fear of gaining weight (or not burning fat or as many calories) if you eat before a workout.
• Using fasted workouts as a reason to "burn" the calories consumed the day before.

Many athletes are drawn to fasted workouts for performance gains but it's very easy to overuse or misuse fasted training as a way to manipulate body composition due to an unhealthy relationship with food and body. 

In my professional opinion, I am not a fan of fasted training. While fasted training may increase fat oxidation rates, there's little to no evidence that specifically working out on an empty stomach will enhance performance. Fasted workouts will increase the stress on the body in addition to the stress that is caused by life and training. There are many other areas to focus your time and energy on that will bring you far better gains in performance and body composition.

Consistent training (with a fueled body) is an effective way to increase the capacity of fat oxidation. Through training, you generate more mitchondria, more enzymes, more transport proteins, better muscle blood supply and faster breakdown of triglycerides into fatty acids. The end result is a greater capacity to burn fat. In other words: fasted training is not needed to become better at fat burning. 

 
If you have not achieved at least 90% of your athletic potential through years of consistent training, healthy lifestyle habits, good restful sleep, proper recovery and optimizing mental health, you shouldn't be chasing the final 10%. The 90% are the real magic bullets that will help you optimize your health and performance. 

When should you perform fasted workouts?

 

Proponents of training in a fasted (or carbohydrate-depleted state) claim that exercising when your body's glycogen stores are low (or depleted), will improve fat metabolism.  Teaching the body to rely on the massive energy supply that fat provides as a fuel source is often referred to as "metablic efficiency" or "fat adapted." These sexy terms are frequently used among endurance athletes and can be intriguing when associated with phrases like;

Burn more fat. 
Minimize the risk of bonking.
Reduced relience on sport nutrition (ex. exogenous fuel sources) during training. 
Minimize the incidence of GI issues. 
Body composition changes. 
Steady energy. 
Sparing glycogen.

It's understandable how the above claims of fasted training can be appealing to endurance athletes. But with much of the available literature studying the effects of fasted workouts and carbohydrate-restricted diets concluding that there is no correlation with enhanced performances in endurance athletes and exercising in the fed versus fasted state shows no difference in body weight/composition changes, why are so many athletes easily persuaded to intentional restrict carbohydrates before workouts? 

While being a better fat burning is enticing for the endurance athlete who is seeking a performance boost, many athletes are primarily drawn to fasted workouts for the reasons of weight loss and/or body composition changes. Because fasted workouts are a frequent practice among endurance athletes, I have talked about this misued and misinformed nutritional strategy at nauseum for over a decade. 

But it would be wrong of me to deprive all athletes of this nutritional intervention so I came up with a list of 38 "nail the basics" lifestyle, training and nutrition strategies that will yield much bigger improvements in fitness, performance, body composition and health than restricting carbohydrates and intentionally 'not eating' before your workouts. 

So there you have it. Once you have nailed the 99% and have reached your genetic potential over many many many years by nailing the basics, you are ready to focus on the 1% - the marginal gains. In other words, the physical and physiological changes that you will experience by prioritizing quality of training, becoming very strong, durable and economical, focusing on your lifestyle habits to keep your body in good mental and physical health and staying consistent with training, will take you much further than restricting carbohydrates in your diet or implementing fasted workouts into your training plan. 

And if this doesn't encourage you to nix the fasted workouts, I encourage you to check in with yourself about why you are fasting or restricting carbohydrates. For some athletes, the act of food restriction can bring on a sense of achievement, pride or self-control, having nothing to do with health and performance. This can be very harmful to your mental and physical well-being.

The original intent of becoming more health-conscious or wanting to improve performance can easily transition into something more severe, such as as a way to severely restrict calories, as an excuse to skip meals, feeling deeply afraid of gaining weight, having feelings of guilt when eating carbohydrates or intense fear of being fat. If you feel your effort for improved performance or healthy eating has gone too far and you are sabotaging your physical and mental health and development as an athlete, I encourage you to find a dietitian or who specializes in eating disorders to help you learn how to better fuel and nourish your body. 

Sources: 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4242477/
https://www.eatingdisorderhope.com/blog/is-intermittent-fasting-actually-a-symptom-of-an-eating-disorder
https://runningmagazine.ca/health-nutrition/new-study-says-fasted-workouts-dont-improve-endurance-performance/
https://jissn.biomedcentral.com/articles/10.1186/s12970-021-00435-3#Sec12
https://www.mysportscience.com/post/2015/04/02/fat-burning-how-does-it-work

Fasted workouts - are they really working for you?

Fasted workouts are stressful. By working out on an empty stomach, you are introducing another level of stress to your body. Even if research says you are teaching your body how to adapt to become better equipped to utilizing fat as a fuel source – this doesn’t mean this approach will work for you.
For this marginal gain approach to truly work, you need to carefully program rest and proper nutrition around your fasted workout so you can recover and refuel properly for this approach to work. Additionally, training needs to be manipulated in a way that you are actually taping into fat burning during the workout - which can be difficult to quantitively measure.

My advice: Nail the basics first. A well balanced diet, good sleep (at least 7-8 hours), mobility, good recovery – get all these things dialed in before you attempt incoroprating fasted workouts into your training. Without a solid foundation of nailing the basics, you risk under performing during your workouts and the risk for injury, sickness and fluctuating energy levels increase.

Despite clear benefits of pre-workout carbohydrate ingestion on improved performance, mental focus, immune system health and longevity in sport, athletes still refuse to intentionally not eat before early morning workouts. What's the most common reason why?

"I need to burn fat for fuel to become more metabolically efficient."

In my opinion, this is the number one reason why athletes intentionally restrict/avoid consuming carbohydrates before an early morning workout. The primary science behind fasting relates to its metabolic effects - by working out on an empty stomach, fat burning is enhanced. Although there are several different approaches to dietary manipulation in an effort to train the muscles to more readily use fat as a substrate, let's put science/research aside for a second and look beyond a cellular level. 

As an athlete, your training is designed to prepare you for your upcoming event. In order to do so, you need to be consistent with training and your body needs to adapt to the training sessions - some of which will be short, some are high volume, some are easy and some are very intense. Knowing that your body is utilizing different fuel sources to adapt to different training sessions, it is very difficult to know which workouts are truly metabolizing fat for fuel. In other words, you are likely underfueling and sabotaging most of your workouts. Additionally, training yourself to become a great fat burner doesn't ensure that you will excel on race day - there are many factors from mental to environmental that will affect your race day performance. It's unlikely that your body fat percentage or fat burning capabilities will be your primary limiter on race day. Being a great fat burner will do nothing for you if you aren't an efficient open water swimmer or if you don't know how to manage the terrain while riding your bike for 112 miles on rolling hills and in the wind. 

As you balance work, family/kids, training and a busy life, is not eating before an early morning workout really making a significant impact in your athletic development? 

Keeping in mind that most athletes nullify the effects of a fasted workout by being sedentary throughout the day, skipping meals (or overeating), being overly stressed and overworked and skimping on restful sleep, you'll do your body and mind a great favor by fueling yourself for the workout training stress. And once again, if you aren't putting effort into your sleep, eating, hydration and recovery habits, the occasional or regular fasted training session is likely hurting your performance, more than it's helping.

Karel and myself eat before every workout and consume sport nutrition during every workout - all year long. Even after a combined 29 IM performances and 9 Ironman World Championship finishes, we still choose a smart fueling approach over a marginal gain approach. 

Eating before a workout and fueling during a workout gives you confidence that you are doing the small things well. And overtime, the small things will add up to something great with your performance.

Remember – there are no shortcuts, hacks or quick fixes to improving your performance. Consistent training, hard work, patience and keeping yourself in great health will help pave the way to great future performances.

For more information on nutrient timing, I dedicated three (very detailed) chapters to this topic in my book Essential Sports Nutrition. 

Pre-workout: To eat or not to eat?

One of the greatest challenges for an endurance athlete is translating the fitness gained in training into a great race day result. Interestingly, far too many athletes don't compete based on repeated training-related decisions. As an example, many (if not most) athletes tend to underfuel in training and overfuel before and during race day. To feel confident for race day, you need to feel confident with your training-related nutrition decisions. Therefore, train like you want to compete.

It seems obvious that if you want to excel on race day, you should make repeated decisions in training that help you prepare for your upcoming race. Rushed and busy schedules, poor planning, misguidance from social media "experts", a complicated relationship with food and the body and unhealthy lifestyle habits make it easy to check off workouts without making significant gains in performance. Unfortunately, athletic success doesn't occur when you are a dedicated exerciser who just checks off workouts. You must give 100% into your training, which means focusing on any and every aspect that will help your body better adapt (and recover) from training stress.

Because different nutritional training methods can be used to obtain specific goals, I'm not here to tell you that you have to eat before your workout. However, I feel it's essential to focus on every way possible to achieve a high level of quality training to optimize long-term training adaptations and overall health. Despite clear benefits of pre-workout carbohydrate ingestion on improved performance, mental focus, immune system health and longevity in sport, athletes still refuse to intentionally not eat before early morning workouts. Here are the most common reasons why:

1. I need to burn fat for fuel - In my opinion, this is the number one reason why athletes intentionally restrict/avoid consuming carbohydrates before an early morning workout. The primary science behind fasting relates to its metabolic effects - by working out on an empty stomach, fat burning is enhanced. Although there are several different approaches to manipulate the diet in an effort to train the muscles to more readily use fat as a substrate, let's put science aside for a second and look beyond a cellular level. As an athlete, your training is designed to prepare you for your upcoming event - not prepare you for a weight loss competition. Will a small difference in your body fat percentage make a significant difference in your race day performance? Additionally, training yourself to become a great fat burner doesn't always equate to being a great athlete on race day for so many factors affect your race day performance. It's unlikely that your body fat percentage or fat burning capabilities are your primary limiter for why you are unable to perform to your potential on race day. As you balance work, family/kids, training and a busy life, you must ask yourself if optimizing fat oxidation by not eating before an early morning workout is making a substantial difference in your athletic development? Keeping in mind that most athletes nullify the effects of a fasted workout by being sedentary throughout the day, skipping meals (or overeating) and skimping on restful sleep, I feel it's better to fuel to perform a quality training session. If you aren't putting effort into your sleep, eating, hydration and recovery habits, the occasional or regular fasted training session could be hurting your performance, more than it's helping.
2. I feel nauseous and lightheaded when I eat before a workout - Whereas not eating before an early morning workout may cause a drop in blood sugar (due to low liver glycogen stores), eating carbohydrates in the hour before exercise can cause reactive (or rebound) hypoglycemia. I actually suffer from this and will often get a bit lightheaded in the 15-20 minutes before/during my workout. However, it always goes away and has no impact on my performance. Symptoms include weakness, nausea and dizziness in the first 20 minutes of exercise. Certainly one would think these symptoms would have a negative impact on performance but that's not always the case. Interestingly, some athletes are more sensitive to carbohydrate feedings than others and some athletes are more sensitive to even the slightest drop in blood sugar than others so the key is understanding your body and what works best for your body. Not eating is not the only solution. If you suffer from reactive hypoglycemia, the solution is not to skip the pre-workout meal as you need to figure out the best way to fuel for your longer sessions and upcoming events. A better strategy is to figure out what, how much and when to eat. I suggest to choose lower glycemic carbohydrates that elicit less of a glycemic response and to combine with a little fat and protein to help slow down digestion in the 90 minutes before exercise. You can also try sipping on a sport drink in the 30 minutes before exercise (continue to sip periodically throughout the first 5-20 minutes of training). Because the symptoms of low blood sugar can often be confused with low blood pressure, it's important for athletes (especially female athletes when menstruating) to focus on pre workout sodium and fluid intake as well as rehydration strategies post workout.
3. I don't have enough time to eat before a morning workout or I have no appetite to eat so early in the morning - This makes sense. If an athlete is waking up at 4am and working out at 430am, is there even enough time to digest a meal? Should you force yourself to eat even if you aren't hungry? The answer to this question goes back to the beginning of this blog - setting yourself up for quality training sessions. If you are an athlete who wakes up at 4am for a workout, your first focus is on getting enough sleep prior to the workout to ensure an upcoming quality training session. Seven to eight restful hours of sleep is encouraged for athletes so if you are falling asleep by 8pm and can sleep restfully through the night, my advice is to push back the workout by 15 minutes to allow a good 30-45 minutes to digest a pre workout snack of 100-200 calories before a one+ hour workout. If the workout is only 30-60 minutes, you can simply sip on a 100ish calorie sport drink in the 5-10 minutes before the workout and continue to sip throughout the training session to offset depleted liver glycogen stores from the overnight fast. If you struggle to eat before a workout due to no appetite, it's worth exploring your eating patterns/choices throughout the day (and through the late evening). Ideally, you want to train yourself not to overeat in the evening so you can wake-up feeling somewhat empty in the stomach. The body's normal digestive rhythm can be trained (so can the appetite). Once again, not eating will not sure a quality training session, especially if the workout is intense or of high duration. And don't get me started on the sleep deprived athlete who sacrifices sleep in order to train....
4. My stomach gets upset if I eat before a morning workout - Just like you train your muscles, the gut needs time to be trained. Some athletes can eat a big meal in the 20 minutes before a workout whereas other athletes feel uncomfortable by the thought of food in the belly before a workout. First off, it's important to focus on your inner dialogue and the thoughts that may be stressing you out when it comes to eating before a workout. "I feel fat, I don't like food in my belly, I need to lose weight..." can actually increase the risk for digestive distress. It's important to develop a healthy relationship with food and see food as a way to enhance your performance and health. Food is not the enemy. Not eating before a workout doesn't make you a fitter, stronger, healthier or faster athlete. It's ok to feel food in your belly before a workout.
   If you are suffering from a more serious issue such as loose stools, nausea, diarrhea, etc. a slow, step-by-step process is needed. First off, avoid high fiber/fat foods in the 6-8 hours before you go to sleep the night before an early morning workout. Secondly, make sure you are well hydrated during the day and consuming adequate fiber consumption in the daily diet to promote healthy and regular bowel movements. Next, I suggest to start training your gut by consuming a very small portion of a low residue food, like saltine crackers, applesauce or a rice cake in the 30-45 minutes before a very easy workout. As you build up a tolerance, try these foods before more intense sessions. Then, work your way up with more calories and try out different food options. Lastly, you need to train your bowels so that you can go to the bathroom before you workout, which may require that you eating standing up, move around before you start your workout, drinking something hot/warm before your workout or planning a pit stop in the first 10-15 minutes of your workout. Overtime, your digestive system should become more regular so that you are not compromised by digestive issues during your training session. Constipation, stress, poor sleep, a nutrient-poor diet and traveling through multiple time zones can through off you bowel movements so be mindful of how your body is impacted by your day-to-day lifestyle habits. 

For more information on nutrient timing, I dedicated three (very detailed) chapters to this topic in my book Essential Sports Nutrition.