Whether or not to eat before a workout is a common question for morning gym-goers. The answer depends on the goals you’re hoping to achieve. For some, skipping a pre-workout snack could leave you in a fasted state. Let’s take a look at why fasted workouts may or may not be right for you.
The practice of intermittent fasting goes beyond working out on an empty stomach or when hungry. It’s possible to feel hungry without being in a fasted state and to feel no hunger when in a fasted state, so don’t let appetite dictate this practice. To truly be in a fasted state, the body should be unfed (no calories at all) for at least 8 hours. Many intermittent fasting plans advise a minimum of 12 hours unfed to be considered fasting. While athletes could take measures to fast during the day for evening sessions, most often, the fasted training is completed first thing in the morning after an overnight fast and before any additional calories are ingested.
A lot of attention has been focused on the idea that exercising in a fasted state aids weight loss. This idea stems from the theory that without fuel, the body pulls from energy stores and relies more heavily on utilizing stored fat. It is a promising theory that when exercising in a fasted state, free fatty acids are utilized more efficiently as a fuel source. In a fasted state, there is a greater utilization of fat as fuel which can positively impact weight reduction.
However, there is a catch. This type of training can lead to breaking down muscle mass, meaning the weight loss isn’t in the typically desired increase in lean tissue and decrease in fatty tissue. One study found no changes in bodyweight or composition between those working out in a fasted versus fed state when looking at male and female athletes which was later backed up by additional research.
Another issue with long-term body composition changes is that if daily fasted workouts are performed, cortisol (the stress hormone that is elevated during an overnight fast) remains chronically elevated, which is known to promote abdominal fat storage. Also, a body in need of calories can go into a state of starvation and lower metabolism to conserve energy when fuel is scarce. Researchers found that when carbohydrates are ingested prior to a workout, the body ramps up utilization of the just-consumed carbohydrates as well as stored carbohydrates. Working out in a fasted state can make the effort feel harder, even if it isn’t, which can lead to reduced effort during the workout and fewer calories burned overall. On the positive side, for untrained athletes who have more weight to lose and more athletic improvements to gain, fasted workouts could be more beneficial in improving fat loss. Also, if limiting calories before exercise contributes, to an overall deficit in calories consumed daily, it could positively impact weight loss results.
When it comes to boosting performance, it is thought that completing training in a low-glycogen state promotes adaptations that allow the body to perform better. Training in a fasted state can increase activities of enzymes involved in energy metabolism and mitochondria formation. These adaptations are thought to improve performance. However, while these adaptations can occur, research has yet to show those adaptations translate into increased performance.
As mentioned earlier, increases in muscle tissue breakdown can lead to decreased performance, especially in power and strength activities. If training in an unfed state makes you feel tired and too depleted to effectively meet performance markers (speeds, distances, time, power), then it might work against your performance in the long run.
One study conducted on cyclists either in a low-glycogen state or normal-glycogen state found endurance performance was relatively equal (no statistical difference), however, sprint efforts completed throughout the endurance time trial were compromised in the low-glycogen athletes. It is a probable notion that intensity is diminished during fasted-state training. One potential benefit of this practice is to become accustomed to training in a less-than-optimal state which can reduce the perceived effects of hitting the wall or be able to maintain efforts in sports where consuming adequate fuel is difficult to impossible, such as open-water swims and technical mountain bike racing.
This category is less scientifically structured and more about doing what works best for your body and individual needs. Basically, if the thought of early eating before a morning workout makes you want to gag or stresses you out due to time and preparation factors, then simply skip it.
For those with sensitive stomachs, working out on empty can also provide relief from gastric upset. If the training session is relatively short in duration and you aren’t going for optimal performance, you are not likely to suffer from not consuming food beforehand. However, if you wake up hungry and have to try hard to overcome that hunger, it can cause stress which works against weight loss. Being preoccupied with hunger can also leave you less focused on the training at hand and putting less effort into the session.
In conclusion, fasted workouts can be periodically incorporated into a training schedule without drastic positive or negative results. When weight loss is the motivating factor, it will likely pay off more to concentrate on the diet as a whole; choosing nutrient-dense, balanced meals and paying attention to not eating too much on a daily basis will likely yield more impressive results than skipping the pre-workout meal. When workouts happen early with no time to eat and digest beforehand, try boosting energy with carb rinsing; the act of sipping a carbohydrate rich beverage, swishing it in your mouth and spitting it out. If performance is your goal, save the fasted workouts for easy, short sessions and add fuel to sessions requiring intensity, focus, and endurance.
Fasted workouts, regardless of the motivating factor, should be kept to less than 90 minutes of training and attention should be paid to consuming a nutrient-, carbohydrate- and protein-rich recovery meal immediately after the session to help minimize lean tissue losses and provide energy to a body in need. Having a mix of fasted and fed training sessions is potentially more effective for improving weight and performance than relying on one or the other method exclusively.
In the end, more research is needed on long-term outcomes of fasted training regimens, different effects between male and female athletes and different effects between training and untrained athletes to produce clear and impactful guidelines. If you are interested in experimenting with fasted workouts, consult a sports dietitian and athletic coach to work with you on optimizing diet and training methods.