The buzz on fasted workouts has been the hot talk of science for some time, with research revealing a host of benefits—from enhanced energy utilization to improved insulin sensitivity.
Whether it’s a personal choice or simply hitting the gym first thing, working out on an empty stomach has grown in popularity.
“Some studies and research suggest that training fasted can better tap into energy needs less from glycogen and more from fat stores, and so in this case, training in a fasted state is better for fat/lipid burning utilization,” explains Douglas Smith, “The very nature of stopping to eat at dinner, sleeping, staying fasted upon waking and then working out means much of our energy needs can come from fat.”
The American Council on Exercise backs such findings that exercising in a fasted state helps contribute to burning fat more rapidly as our glycogen storage, used for energy, is low. This is great news for those looking to shed a few pounds.
On the flip side, some experts argue that a lack of energy will reduce the intensity of sessions, negating the positive effects. In this case, fasted workouts would be more suitable for those with specific goals, personal eating habits, and preferred workout time.
Read on to learn all about fasted workouts, including the best time to do them, what to eat after, and more.
Meet the Expert
- Lori Russell, MS, RD, CSSD, CPT, is a Swisse Wellness Consultant @HungryForResults.
- Douglas Smith is a co-founder and CEO of True Nutrition.
When is the Best Time to Workout Fasted, and For How Long?
According to Lori Russell, to truly be a fasted workout, there needs to be a span of 10-12 hours between your last meal and the training session. “This makes morning sessions the most practical, and while you should avoid calories before fasted training, it is beneficial to have a big glass of water to maintain hydration levels and take a multivitamin to help prevent any nutrient deficiencies.”
As the body is not utilizing energy for digestion, many people feel more energized during fasted workouts and can sail through a 60-minute session with ease. “It also highly depends on what we define as working out, given a 30-minute jog in the neighborhood versus a 45-minute training session at the gym tap into different energy needs,” explains Smith. “But when an ideal workout is a four-hour hike up a mountain or something more strenuous, being fasted might not be the best idea, and maybe it's best to break your fast halfway through your workout to fuel the body with an exterior energy source.”
The key is to maintain a healthy balance between burning those calories and dramatically depleting energy stores in the body, which can cause harm in the long term.
How Long Should You Wait to Eat After a Fasted Workout?
“Some notions and studies are suggesting that eating after 30 minutes will help the body absorb nutrients more efficiently than just eating whenever possible,” says Smith. “The act of working out is a body stressor and creates a biological environment for your body to require feeding. Eating healthy foods can help utilize the natural spike in insulin when you do break a fast to better help and shuttle nutrients to the parts of the body that need it the most, the actual musculature you trained minutes before.”
With busy schedules and many of us on the go, or perhaps the hunger pangs have not yet set in, eating a nutritious post-workout meal is not always immediately possible. However, according to Smith, this isn’t necessarily an issue. “Whilst many swear by the 30-minute protocol, it's really a trial and error scenario for most people, and self-experimentation is crucial to see if it's beneficial or not for yourself.”
Who Should Avoid Fasted Workouts?
From a health perspective, fasted workouts may not be suitable for everyone, and it’s crucial to understand what is safe for your body. According to Russell, any adult with a health condition and pregnant women should discuss their desire for fasted workouts with a dietitian and medical physician before diving in.
Similarly, Smith advises: “In a medical sense, fasted exercise may not be suitable for anyone who has a health condition, such as hypoglycemia, or some other metabolic condition that would hinder the ability to workout utilizing energy sources that weren't just consumed. Fasted workouts are an extensive process for the human body, and some may feel they need energy from food beforehand and will need to slowly adjust to exercising on an empty stomach.”
That’s not to say the latter should avoid fasted workouts, rather allow the body time to break through the initial challenges to adapt to this new format.
Which Workouts Are Best in a Fasted State?
Alongside their convenience, fasted workouts are generally performed to guide the body toward a specific goal. “Workouts on an empty stomach are done with the intent to enhance future adaptations and future performances, and not just for immediate results. This means the actual fasted workout is not going to feel great as your body is deprived of an immediate energy source,” explains Smith. “Shorter bursts of exercise are more efficient in this case, as given a drop in insulin levels, our bodies naturally tap into fat as its main source of fuel.”
This means quick, high-energy bursts of cardio are popular, such as short spurts of high-intensity interval training to reap optimum fat-burning potential. In fact, a study by Northumbria University found that it’s possible to burn up to 20% more body fat by exercising in the morning on an empty stomach, without it affecting our hunger later in the day.
However, in contrast, a study conducted by The Results Journal of the International Society of Sports Nutrition on fasted versus fed aerobic exercise on 20 healthy females eating a similar calorie intake found no difference in results from the baseline measure.
Furthermore, some science also suggests that fasted workouts are not best advised for those trying to build muscle mass, given glycogen is a preferred source of fuel than fat for this type of workout, resulting in a potential drop in permanence and shorter workouts with reduced impact. Smith also suggests we: “Skip fasted workouts for key sessions when you are looking to see high power or speed, and should also be skipped when stress levels are high, as this can disrupt hormone balance even further.”
So, whilst some research has found a positive impact on fat burning during fasted workouts, ultimately, the choice to work out fasted comes down to personal preference rather than hard-backed science.
What Should You Eat After Your Fasted Workout?
Certain foods provide better nutritional sources than others to refuel our bodies, so before you reach for a sugary treat for an energy boost, read on.
“Refuelling after a workout is very important to start the recovery process of building lean tissue and replenishing glycogen stores, and this becomes more crucial if the workout was done in the fasted state,” says Russell. “A quick snack containing a 3:1 or 4:1 ratio of carbohydrate to protein is the best for an immediate refuel, with a protein smoothie, chocolate milk, eggs and toast, or Greek yogurt and fruit excellent choices.”
For others, a source higher in protein is the preferred choice to break the fast. “It’s highly dependent on the individual, but I find a meal higher in protein and lower in carbohydrates and fats to be most beneficial,” outlines Smith.” But again, this might be the time to consume the majority of your carbohydrate-rich foods, with self-experimentation key here. But regardless, eating the most nutrient-dense foods is critical at this time as the body is primed for receiving these nutrients, given it just underwent stress.”
Whether you want to utilize fat as fuel, improve your cardio stamina or sneak in a morning workout before all else, fasted workouts, like most fitness trends, have their pros and cons. But with trial and error, they may just become your favored go-to. Why not try it and see for yourself?