Debbie Potts Coaching

When to eat or not to eat before exercise?

What does the research say on FASTED exercise vs. FED Exercise for:

  1. Endurance athletes
  2. HIIT training
  3. Strength training
  4. Fat loss goals
  5. Performance goals
  6. Longevity goals
  7. Female athlete
  8. Male athlete

Let’ review current research and articles but remember N = 1

Effects of fasted vs fed-state exercise on performance and post-exercise metabolism: A systematic review and meta-analysis


The effects of nutrition on exercise metabolism and performance remain an important topic among sports scientists, clinical, and athletic populations. Recently, fasted exercise has garnered interest as a beneficial stimulus which induces superior metabolic adaptations to fed exercise in key peripheral tissues. Conversely, pre-exercise feeding augments exercise performance compared with fasting conditions. Given these seemingly divergent effects on performance and metabolism, an appraisal of the literature is warranted.

This review determined the effects of fasting vs pre-exercise feeding on continuous aerobic and anaerobic or intermittent exercise performance, and post-exercise metabolic adaptations. A search was performed using the MEDLINE and PubMed search engines.

The literature search identified 46 studies meeting the relevant inclusion criteria. The Delphi list was used to assess study quality. A meta-analysis and meta-regression were performed where appropriate. Findings indicated that pre-exercise feeding enhanced prolonged (P = .012), but not shorter duration aerobic exercise performance (P = .687). Fasted exercise increased post-exercise circulating FFAs (P = .023) compared to fed exercise.

It is evidenced that pre-exercise feeding blunted signaling in skeletal muscle and adipose tissue implicated in regulating components of metabolism, including mitochondrial adaptation and substrate utilization.

This review’s findings support the hypothesis that the fasted and fed conditions can divergently influence exercise metabolism and performance.

Pre-exercise feeding bolsters prolonged aerobic performance, while seminal evidence highlights potential beneficial metabolic adaptations that fasted exercise may induce in peripheral tissues.

However, further research is required to fully elucidate the acute and chronic physiological adaptations to fasted vs fed exercise.


Fasted Cardio?  Is is best for FAT LOSS?

Is it okay to workout on an empty stomach? Ultimately, it depends on your body composition, goals, overall health and preferences.

Working out while fasting, also called “fasted cardio,” does have some advantages — such as potentially leading to more fat loss and preventing indigestion while exercising. On the other hand, it’s not for everybody, since it may make some feel weaker and lethargic while working out.

If you’re curious about how meal timing can affect your workout performance and results, read on to find out about the benefits and drawbacks of working out while in a fasted state.

What Is Fasted Cardio?

Fasted cardio describes doing aerobic or endurance exercise on an empty stomach, without eating anything beforehand. This is called being in a “fasted state,” which is considered to be 4 to 6+ hours after your last meal or snack.

In order for you to truly be in a fasted state, in which your glycogen levels are low, some experts say you’d have to go more than 9–10 hours without eating anything. Fat and carbohydrates are the most important fuel sources for skeletal muscle ATP synthesis, so when carbohydrates are mostly not available due to fasting, fat is utilized instead.

Most people do fasted cardio workouts in the morning, before eating anything for breakfast. This may mean that someone has been fasting for 8 to 16 hours or more overnight, depending on their schedule and when they stop eating at night. For many people, the morning is the easiest time to workout without any “fuel” in their system because they’ve just gotten up and have already fasted through the night.

Related: A Beginner’s Guide to Intermittent Fasting

Health Benefits

What are the benefits of fasted cardio? Based on available research, here’s what we know about the potential perks of working out without any food in your system:

1. May Boost Fat Burning and Weight Loss

Does fasted cardio actually work for weight loss? There’s some evidence from studies suggesting that it can. Researchers involved in a 2016 meta analysis concluded that “aerobic exercise performed in the fasted state induces higher fat oxidation than exercise performed in the fed state.”

When in a fasted state, your body doesn’t have any glucose/glycogen available to be used as a quick source of energy, so it utilizes stored energy instead.

This means that your body pulls from energy stored in your muscles and from stored body fat (via fat lipolysis and fat oxidation) in order to keep you fueled. Lipolysis is the metabolic pathway through which lipid triglycerides are broken down into fatty acids and glycerol to be utilized during fasting or intense exercise. The result is that you may boost your “fat burning” potential, although it’s likely not to have a dramatic effect in most cases.

Another way in which fasted cardio may support fat loss is by spiking post-exercise calorie-burning. Essentially after your fasted workout is done, your body uses up extra calories to help you recover, which raises your metabolic rate a bit for about 24 hours.

That being said, not every study has found this benefit to be true. A 2020 article published in the Open Access Journal of Sports Medicine states that “Our review of the literature suggests that there is little evidence to support the notion of endurance training and fasting-mediated increases in fat oxidation, and we recommend that endurance athletes should avoid high intensity training while fasting.”

The researchers add that …

Fasting decreases body weight, lean body and fat content in both trained and untrained individuals … However, there are conflicting data regarding the effects of fasting on glucose metabolism in highly trained athletes … Differences in experimental design, severity of calorie restriction, duration, and participant characteristics could, at least in part, explain such discordant finding.

2. Can Decrease Nausea

If you struggle with feeling nauseous while exercising, is it good to workout on an empty stomach in the morning? It can be, assuming that a full or partially full stomach is to blame for your indigestion. If eating before doing cardio makes you feel uncomfortable, you can try either having nothing beforehand and perhaps some water or coffee.

If you find that the sensations of “lightness” in your stomach feels better while exercising, then fasted cardio might be a good fit for you.

Everyone is a bit different when it comes to their eating preferences around workouts; some like a small pre-workout snack before exercising, some prefer a bigger meal a couple hours before a workout, and others like to consume nothing at all. Feel free to experiment and see what works best for you.


1. Might Make You Feel Fatigued More Easily

There’s a chance that fasted cardio might cut your workout short if you leads you to feel tired and unmotivated more easily. Again, this comes down to the individual.

Overall, the effects of fasting on physical performance remains unclear, with some studies reporting decreased performance, some showing increased endurance, and others reporting no significant correlation or effects.

If you’re waking up early for a workout after a good night sleep, then you might have plenty of energy even without a meal. However, if you work out later in the morning on an empty stomach, after you’ve already been up for several hours, fatigue might be an issue. So it seems to depend on your unique schedule, body type and other factors.

2. Could Lead to Weakness and Less Power Output

Some find that fasted cardio causes side effects like dizziness, low blood sugar and lightheadedness. You may find that you aren’t able to push yourself as hard when fasted due to feeling weak, in which case you’ll be scarifying physical performance.

For example, one study concluded that “Overnight fasting compromises exercise intensity and volume during sprint interval training but improves high-intensity aerobic endurance.” Another meta analysis uncovered findings indicating that pre-exercise feeding enhanced prolonged, but not shorter duration aerobic exercise performance.

If you tend to experience lethargy when “running on fumes” during a workout, consuming a snack plus water to keep you hydrated before working out can be a better solution than skipping food altogether.

3. May Contribute to Muscle Breakdown

Although we’ve mostly been talking about fasted aerobic workouts, it’s still important to point out that fasted exercise may negatively impact muscle growth and strength.

Some studies have found evidence that fasted workouts cause muscle tissue to be broken down for energy, thereby making it more difficult to put on muscle and to build strength and endurance.

So if you’re into bodybuilding, cross training and lifting weights, there’s potential for fasted aerobic workouts to hinder your results. It’s not a deal breaker, but you’ll want to be mindful about how often and how intensely you do fasted cardio.

Should You Try It?

So what’s the bottom line, is fasted cardio better than fed cardio?

As you can probably tell by now, one approach isn’t necessarily better than the other.

While fasted cardio can offer some benefits for amplifying fat loss, if weight loss is your primary goal, your total energy balance and calorie intake will be the ultimate determinant of whether or not you lose weight.

Keep in mind that you may experience an increased appetite after exercising in a fasted state, which can cause you to overeat afterwards if you’re not careful.

If eating a very calorie-dense meal following a fasted cardio workout causes you to have a positive energy/calorie balance at the end of the day, this isn’t going to help you to reach your weight loss goals.

Here are some things to consider if you do want to give fasted cardio a try:

How long should you do fasted cardio?

Experts tell us that it’s probably best to stick to moderate intensity cardio for up to an hour when fasted. However, if you personally have energy to do even more without feeling negative side effects, a longer or high-intensity workout can also be appropriate.

Your best bet is to probably start out by trying 20–30 minutes of fasted exercise, and then increasing intensity and duration if you feel good doing so. Listen to your body and avoid pushing too hard to the point where you feel lightheaded or famished.

What should you eat after fasted cardio?

You’ll want to fill up on a combination of protein and complex carbohydrates, which help you refuel and support muscle recovery. Fiber and healthy fats are also important components of a healthy post-exercise meal because they’ll help control your appetite and prevent you from overeating.

Some examples of good recovery meals post exercise can include: a protein smoothie with fruit, hemp seeds and coconut milk; a salad with protein and avocado; quinoa with hard boiled eggs and veggies; an open face sandwich with meat/fish/eggs and a side salad dressed with olive oil.

Can you have coffee before fasted cardio?

Most people find that coffee in the morning before working out gives them a welcomed boost of energy that helps them push through a workout. As long as you also drink water to prevent dehydration, and don’t feel jittery or nauseous from having coffee alone, then this seems to be a fine option.

Should you combine intermittent fasting and fasted exercise in the morning?

  • This can be a good strategy if you’re already accustomed to practicing intermittent fasting (IF).
  • People who incorporate IF into their routines likely have more opportunities to do fasted workouts since they are skipping meals anyway, most often breakfast in the morning.
  • You’ll want to listen to your body and look out for weakness and other warning signs, but as long as you feel good combining these two approaches then there’s no reason not to.

Final Thoughts

  • What is fasted cardio?
    • It’s another way to describe working out on an empty stomach.
    • Most often people do this in the morning after they’ve fasted overnight for 8+ hours.
  • Potential benefits of fasted cardio include increased fat burning, help with weight loss, and less indigestion.
    • However, drawbacks can include increased fatigue and weakness while exercising, and a bigger appetite once the workout is over.
  • Does it work for weight loss?
    • It can, but weight loss really depends on someone’s overall day and energy/calorie balance.
    • A fasted workout can slightly boost calorie and fat burning, but in order for weight loss to happen, someone still needs to consume less calories than their body is using each day.

Fasted Cardio: Should You Try It for Fat Loss?


Benefits of Fasted Workouts

In the fasted state, insulin sensitivity increases and so does production of growth hormone. Both of these can boost fat loss, which supports the argument that fasted exercise results in more fat loss.2

The advice to train in a fasted state is a strategy to increase fat burning, with the hope of using some stored fat. For those who practice intermittent fasting, training on an empty stomach can be more convenient because you may have more time available in your schedule during your fasting period.

Drawbacks of Fasted Workouts

The intensity of the exercise you are doing affects whether your body uses fat or glucose as energy fuel. Heavy lifts or fast running will use stored muscle glucose (glycogen) more than fat,3 whether or not you are doing these tough workouts on an empty stomach.

In addition, how much fat and glucose is used as fuel is prioritized over 24 hours in relation to all energy demands, not just those of your workout.4 You may burn some extra fat during a fasted exercise session, but it is not likely to be enough to burn a lot of stored fat when considered overall.

When you exercise too intensely in a fasted state, your muscles can degrade. This is because your body pulls apart amino acids to help preserve critical blood glucose. Also, chronic low blood glucose and rising cortisol (stress hormone) levels can depress the immune system.2

Even though there is some evidence of advantages to fasted workouts, there is also evidence that suggests fueling with carbohydrates and protein before exercise can improve performance, minimize muscle damage, and prevent depletion of glycogen.5

Best Pre-Workout Fuel

The best strategy for burning maximum fat, if that’s your aim, is to eat two hours before weight training or other exercise. If you wake early and like to exercise first thing, have a pre-workout snack, like a piece of toast with honey or an energy bar. Or have a diluted glass of juice or small sports drink during your workout.6 (Eating too much before a workout can lead to stomach upset.)

A mix of carbohydrate and protein is an excellent choice before weight training.5 The carbohydrate gives your body some fuel to enhance performance, and the protein helps your body build muscle in your recovery phase.

By eating a small snack prior to a workout, you can still encourage the fat-burning process without depriving your body of necessary fuel. You also need some calories, protein, and carbohydrates after your workout to help your muscles recover and get stronger.



What effect does fasted exercise have on metabolism?

Exercising before eating can burn fat and improve metabolic flexibility but also affect your fitness performance. Here’s how to strike a healthy balance.

Should I eat before or after I work out? 

From a metabolic health perspective, fasted exercise may be beneficial because of its potential effects on glucose, fat burning, and insulin sensitivity. But the approach can have significant drawbacks for performance, so it isn’t right for everyone. Here’s what you need to know about the effects of fasted exercise on the body—and how it might impact your workout goals and metabolic health.

What does it mean to be fasted?

You might feel like you’re starving after skipping lunch and heading into a 5 pm workout, but depending on how you define it, you haven’t fasted. In terms of gastrointestinal physiology, “fasted” means your body is in a postabsorptive state and the nutrients from your food have been digested, absorbed, and stored in your body, says Dominic D’Agostino, PhD, a Levels advisor and Associate Professor in the Department of Molecular Pharmacology and Physiology at the University of South Florida Morsani College of Medicine. “Generally, that takes about 10 to 14 hours,” he explains.

What happens in the body when exercising while fasting?

The body has a limited energy supply, so it’s purposeful in how and when it uses different types, especially when exercising in a fasted state. This is due to a few changes that occur in the body during fasting, explains Brian Carson, PhD, of the University of Limerick, in Ireland, who researches the roles of exercise and nutrition on metabolism regulation for performance and health.

The best way to understand this is to think of your body as a hybrid car with two fuel tanks. One tank is gas or glycogen (the stored form of glucose), and the other is electricity or fat. The body typically prefers to use “gas” for high-intensity exercise. “If you need it fast and easy, glucose will be the preferred energy source,” says Dr. Carson.

The body’s ability to trade off between carbohydrate and fat metabolism (or switching between tanks) is called metabolic flexibilityThis allows you to easily and efficiently balance the types of energy you use. Training fasted is one way to improve metabolic flexibility because it forces the body to use different energy sources by increasing the availability of fat for fuel.

Note that generally, the body doesn’t run solely on just one fuel source or one type of metabolism only. “It’s very rare that you would use solely fat sources, so you tend to be using some glucose and glycogen throughout [an exercise session],” Dr. Carson says.

However, because the body is fasted and not taking in any new carbohydrates that provide glucose, it will use more fuel from fat sources during exercise, which helps preserve some of that glycogen. “We try to spare [glycogen] for when we might need it later for a fight-or-flight type incident,” says Dr. Carson.

During fasting, the body increases the availability of free fatty acids circulating in the blood through lipolysis, the breakdown of stored fat tissue. The hormones norepinephrine and epinephrine help to mobilize this energy and release those fatty acids into the bloodstream for the body to use. “So, because there’s an increase in the availability of those fatty acids, we’ll see an increased utilization of those fat sources,” says Dr. Carson. As the fast extends, ketone bodies also become available. The liver produces ketone bodies derived from free fatty acids for the body to use as energy when glucose is unavailable.

The effect continues even after fasted exercise, when you’ll see a decrease in overall glucose oxidation (the breakdown of glucose) and insulin circulation and an increase in free fatty acids circulating in the blood. Think of it this way: You just used additional stored energy to exercise in a fasted state, and now the body wants to prioritize restoring the muscles with glycogen. To survive in the meantime, the body needs to use fat stores and run on the “electric tank” so that your muscles can prioritize getting that glycogen back.

“That’s true all the time, even in fed exercise, but in a fasted state, the contribution from fat sources overall is proportionally higher,” Dr. Carson says. Adding protein to carbohydrates to replenish muscle glycogen stores is important because it supports the muscle repair process.

Do fasted workouts help you lose fat?

This is one of the most common assumptions about fasted exercise. However, the generalconsensus among experts—researchers as well as trainers and coaches—seems to be that fasted exercise doesn’t result in more fat loss.

“There’s no doubt that you’re proportionally using more fat during a fasted workout,” says D’Agostino. Meaning that the contribution from fat sources throughout exercise and in the recovery period is greater when conducted in a fasted state.

One 2016 meta-analysis in the British Journal of Nutrition looking at 27 studies found that fasted aerobic exercise induces higher fat oxidation (burns more fat) and leads to a higher acute fat oxidation than exercise performed in the fed state.

A caveat is that the study authors note that the findings aren’t enough to back up long-term effects because fat burning must be considered over the course of days to assess its impact on body composition, as other research notes.

“Twenty-four-hour calorie burn will largely depend upon daily calories consumed and energy balance,” says D’Agostino. If you continue consuming fewer calories than you burn, you’ll experience higher fat burn. “If a person maintains a caloric deficit, there will be a greater elevation of fat oxidation, even independent of macronutrient composition.”

There are studies showing no impact on the fasted condition, but never a benefit greater than the fed condition.—Brian Carson, PhD

Another study in 16 women over six weeks found no difference in fat loss between women who exercised fasted compared to those who exercised after eating over the study period.

Another related issue is post-workout hunger in those who do fasted exercise. Research published in the International Journal of Obesity in 2021 compared those who did fasted exercise and fed exercise with and without a post-exercise meal. Although they found that fasted exercise without a post-exercise meal resulted in the lowest 24-hour energy intake, it also produced the lowest energy expenditure and the highest hunger. That means that although these people had a short-term decrease in energy intake, they burned fewer calories and were hungrier.

How does fasted exercise impact workout results?

Everything depends on your exercise goals and priorities. Fasting vs. non-fasting has a more significant impact when looking at people exercising for more than an hour. A 2018 meta-analysis led by Dr. Carson looked at 23 studies on people doing cardio in the fed vs. fasted state and found no difference in exercise performance when workouts were less than 60 minutes.

“When the performance outcome is less than an hour, in almost 60% of the studies we looked at, performance was not impaired by fasting,” says Dr. Carson. So if you’re working out for a short time in a fasted state, your performance might not suffer. If performing at your best isn’t the purpose of your workout, like during a quick recovery walk or casual weekend jog, then doing so in a fasted state isn’t a problem. “There are studies showing no impact on the fasted condition, but never a benefit greater than the fed condition,” says Dr. Carson.

For those prioritizing performance goals, gaining strength or muscle, or those who like high endurance and high-intensity workouts, exercising in a fasted state could negatively affect your workout results.

Research also suggests that performance improves when you eat before longer workouts. The meta-analysis led by Dr. Carson and published in the Scandinavian Journal of Medicine & Science in Sports found that 54% of studies showed that pre-exercise feeding improved performance for people doing aerobic exercise for longer than 60 minutes, possibly due to the additional glycogen that’s available to help fuel the workout. The key takeaway: According to Dr. Carson, if you have a long exercise session or are performing in some kind of long race, you should fuel to perform to your maximum.

For people looking to gain strength and muscle mass, there’s no reason to train in a fasted state. “Do we lose muscle mass because of fasted training? No. But is it going to make your muscles bigger? No,” Dr. Carson says.

A small study on 16 men doing resistance training found that not eating breakfast before exercising decreased exercise performance in the gym. Plus, research on muscle, strength, and fasted training highlights that eating protein post-exercise is most important for recovery when exercising fasted.

It’s worth noting that other research suggests that while exercising in a fasted state may impair  performance in a particular workout, doing it repeatedly could lead to beneficial adaptations over time, such as improved glucose control and fat burning.

What’s the bottom line?

Fasted exercise could be helpful for those who want to optimize metabolic health and help the body to be metabolically flexible.

  • The benefits of fasting include reduced concentrations of many metabolic biomarkers associated with chronic disease, including insulin and glucose.
  • Exercising fasted can help your body switch fuel sources.
  • Using or metabolizing different types of energy like fat during exercise is great for when you want more sustained energy while keeping your insulin low.
  • “Low levels of fasting insulin are a sign of higher insulin sensitivity, higher fat oxidation, and low metabolic disease risk. 
  • Overall, it’s an excellent biomarker for optimal metabolic health,” says D’Agostino.

If you’re looking to maximize performance (via an endurance sport or in time trials), you’ll likely best be served by exercising fed. The same goes for the day that people compete in a triathlon—there aren’t reasons to fast for performance on the day of.

Another essential point: Exercise itself is king.

Research has found that staying active improves insulin sensitivityboosts endorphinsreduces cardiovascular risk, and helps you stay healthy longer.

“What you would hope to achieve from fasted training is an additional ability or enhanced ability to utilize fat as a fuel source during exercise,”

Dr. Carson says. “But again, the training and the exercise itself will provide most of the adaptation. We may be able to augment that adaptation to a certain extent by doing our training in the fasted state.”

One important caveat: most of the research done in this space is on exercise and fasting in the morning—eating breakfast or not before a workout. It’s not clear what the effects might be for evening exercise.

For those who want to try fasted exercise for the first time, Dr. Carson suggests doing so when performance isn’t your main priority.

Again, this means you don’t want to exercise fasted the day of your half marathon, but rather in some prior training sessions.

“What I recommend is that the fasting period is a minimum of 10 hours, closer to 12 If possible,” Dr. Carson says. “So it looks like maybe having your dinner before 8 pm, then exercising before 8 am the following morning.” 

Trying fasted exercise might take some trial and error. So pay attention to how you feel during and after fasted training, and do what’s most comfortable for you and your goals.

The Pros and Cons of Fasted Workouts

If you’re an active female, chances are you’re at risk for low energy availability and the health consequences it brings. Here’s what you need to know. 

When researchers screen the nutritional intake of female athletes, a staggering percentage are not eating enough to support their performance and their health.

Here are just a few examples of how many female athletes in various sports were at risk for low energy availability (LEA) and the detrimental health consequences it brings, according to recent research:

  •  Nearly 80 percent of elite female cross-country runners show risk for LEA in this study.
  •  88 percent of professional female soccer players had LEA in this study.
  •  96 percent of ballet dancers had LEA in this study.
  •  100 percent of synchronized swimmers had low energy availability in this study!

More broadly speaking, a 2022 study of more than 200 female endurance athletes published in Frontiers in Sport and Active Living reported that 65 percent were at risk of LEA, 23 percent were at risk of exercise addiction, and 21 percent had disordered eating behavior. 

LEA is a problem I see every day, and if it isn’t caught in time, it can sometimes lead to irreversible damage to your health, such as dangerously low bone mineral density.

What is LEA?

Technically speaking, low energy availability, or LEA, is defined as having limited energy available to support your normal body functions once your energy expended through exercise is subtracted from your total dietary energy intake.

Plainly speaking, that means you’re not eating enough to support both your training and your basic biological needs. This is what makes LEA particularly insidious. You may be able to run, swim, bike, lift and otherwise complete your workouts (at least for a while), but your body doesn’t have enough calories and nutrition left over to keep your organ systems operating at optimal levels.

When this happens, your body enters a state of LEA, which my former Ph.D. student and now doctorate specializing in LEA, Dr. Katie Schofield, likens to how your phone goes into low battery mode: it still functions, but the screen goes dim, and some of the apps start shutting down to conserve energy. Only in the case of your body, those “apps” are your organ systems, like your reproductive and endocrine systems!

What Are the Impacts of LEA?

Prolonged LEA can have serious consequences on your health. One of the most notable consequences is on your reproductive system. Many women still believe that it’s “normal” for female athletes to lose their periods when they train. It is far too common. But it is NOT normal! Research shows that when women dip into LEA, it disrupts the production of luteinizing hormone, which plays an important role in ovulation and regulating the menstrual cycle.

One of the downstream consequences of disrupting your hormones with LEA is serious and potentially lasting negative impacts on your skeletal system. Without enough energy, your osteoblasts (the cells that build bone) and osteoclasts (the cells that break down and resorb bone) can’t do their job properly, and you end up breaking down more than you build up. The end result is bone stress injuries and stress fractures, as well as an increased risk for osteoporosis down the line.

LEA also can lead to a host of other health disruptions, including irritability, bouts of depression, brain fog, depressed immunity, loss of libido, GI issues like constipation and diarrhea, and can lead to nutritional problems like anemia.

It seems obvious that LEA can also hurt your performance. But here’s the problem: depending on your sport, you might not see decrements, and may even see some improvements, for a period of time, because remember, LEA is about not having enough energy left over after training, not for training per se. So though chronic LEA negatively influences muscular adaptations and muscle protein synthesis, research shows that it may fly under the radar for prolonged periods of time before adaptations stagnate and performance declines. Worse, you may already be damaging yourself, such as bone loss, before you reach that point.

How to Spot LEA

It’s important to try to spot LEA before it becomes a serious health problem. Some telltale signs that you are in low energy availability include:

  • Irregular or missing menstrual cycles
  • Fatigue
  • Mood problems, including irritability and depression
  • Frequent illness
  • Frequent injuries, especially stress reactions and fractures
  • Decreased libido
  • Increase in GI issues
  • Poor or decreased training adaptations

How to Get Out of & Avoid LEA

This is the tricky part. There are many reasons female athletes find themselves in a state of LEA. Some are intentional, such as dieting and restricting carbohydrates. Others are unintentional–women think they’re eating enough, but they’re not. And most often, they are not eating in and around training; if you delay food intake after, your body stays in a catabolic (breakdown) state, and your brain registers this as not having enough energy to support adaptation as well as health.  If you have disordered eating, a history of restrictive eating, or an outright eating disorder, working with a professional should be your first step.

If you suspect you’re in LEA unintentionally, becoming more intentional about your fueling is the first step.

Female athletes should aim for a baseline of 45 calories per kilogram of fat-free mass (or lean body weight) per day to meet their energy needs.

They may need even more (i.e., 50 calories per kg) during competition or heavy training periods. Be very cognizant that you are refueling after your training, within 30-45 minutes, to stop the brain from perceiving low energy intake.

That’s 2800 calories a day for a 140lb/64kg female. If that sounds high, it’s because you’ve been conditioned to believe that women should be limiting themselves to 1200 calories a day–a harmful diet-culture message that has absolutely no bearing on active or athletic women.

Though I don’t generally advocate rigidly counting calories and/or tracking macros, it is worth it to keep a tally for three to five days to see how much energy you’re actually taking in versus how much you think you’re taking in. Chances are, you’ll be very surprised!

The next step is increasing your intake around your training, and then across the day, see how you feel and perform when you’re hitting the mark. Again, I bet you’ll be surprised. So many of my athletes reach their optimum performance potential once they finally achieve their energy needs.

Nutrient timing:  the secret to muscle strength gains and recovery

Post-workout fueling matters even more for women than men.

Low energy availability is extremely common in women athletes. A 2019 survey of 1,000 female athletes across more than 40 sports published in the British Journal of Sports Medicine estimated the risk of low energy availability in women athletes at more than 47 percent.

That means nearly half of active, performance-minded women may not be eating enough for their body to perform basic functions like making muscle, regulating metabolism, and maintaining homeostasis after accounting for the energy they use for training.

That’s bad for your health and performance.

Exercise doesn’t work without the nutrition to support it.

Fueling directly around your training can help you avoid going into low energy availability.

While I’ve seen women become more in tune to their pre and during exercise fueling needs, one area that still falls short is recovery. I see too many women who admit to skipping their post-workout snack because they’re trying to lose weight. This is the wrong way to go about it—especially as a woman.

I know the logic seems sound on the surface. It’s easy to think if you delay food post workout, you will prolong your fat burning (since the body has nothing else left to burn) and thereby you will lose weight more effectively. In fact, the opposite happens.

You may end up gaining weight. By withholding recovery fuel, you put your body in a catabolic state that stalls your recovery, dims your metabolism, and increases your fat storage because the body is afraid it is in a state of famine.

Also, kiss lean mass gains goodbye; without adequate energy intake, you might get stronger, but you cannot build muscle.

The better strategy is taking advantage of your recovery window—the time right after exercise when your insulin levels peak, opening multiple metabolic pathways to expedite your glycogen storage and muscle repair process.

During this “golden window” you’re not only primed to transport the carbs you eat straight into your muscle stores, but also to shuttle amino acids into your muscles, where they can repair the damage and build you back stronger.

It’s important to note that as a woman, your recovery window to take advantage of all these benefits is short—about 30 to 45 minutes (whereas men may have up to 3 hours).

After that point, your insulin sensitivity declines, so it takes your muscles longer to absorb the glucose from your bloodstream, and as a result, your overall glycogen storage is lower. In fact, just 2 to 2 1/2 hours later, your glycogen storage rate drops by 50 percent.

Eating immediately after hard exercise delays this decline in insulin sensitivity. That’s especially important for women in the menopausal transition, who may already be more insulin resistant because of the hormonal changes.

Be sure to prioritize protein in that recovery snack. Women even more so than men need protein post workout, and we need it fast. The sex hormone progesterone exacerbates muscle breakdown in women. It makes us more catabolic, especially during the luteal phase of our menstrual cycle. So, you need more protein to protect your muscles and come back stronger. Women recover faster with 25 to 30 grams of protein (with 5 to 7 grams of BCAAs) within 30 minutes of a hard workout.

Pair some carbohydrates with that protein. The two work in harmony to increase your glycogen storage rates. Research also shows that taking in carbohydrate and protein together postexercise helps to reduce inflammation and can boost immunity.

If you delay calorie intake, you stay in a breakdown state. Your body won’t start repairing until you take in some food. Even if you eat enough in the rest of your day to meet what your body needs, not eating post-workout acts the same as not eating enough. And on days when maybe you’re running around and not meeting your total energy needs, properly fueling before and after working out can help you prevent going into a state of low energy availability.

Finally, if you’re planning to make diet adjustments, especially if you’re doing any sort of calorie reduction, consider implementing them outside of your workout fueling – your body will thank you!

Dr. Stacy Sims is a well-known exercise physiologist and nutrition scientist who has dedicated her research to studying female athletes. She has authored several books on the topic, including “Roar: How to Match Your Food and Fitness to Your Female Physiology for Optimum Performance, Great Health, and a Strong, Lean Body for Life.”

Based on her research, Dr. Sims recommends the following fueling strategies for female athletes:

Before exercise:

  • Eat a meal or snack containing carbohydrates, protein, and fat about 2-3 hours before exercise.
  • For longer workouts, eat a high-carbohydrate snack 30-60 minutes before exercise.
  • Drink water or a sports drink to ensure proper hydration.

During exercise:

  • Consume carbohydrates in the form of a sports drink, energy gel, or other easily digestible source.
  • Drink fluids to maintain hydration levels.
  • Consider consuming protein during prolonged workouts to prevent muscle breakdown.

After exercise:

  • Consume a high-quality protein source within 30 minutes of exercise to promote muscle recovery.
  • Eat a meal containing carbohydrates, protein, and fat within 2 hours of exercise to replenish glycogen stores and promote muscle recovery.
  • Drink plenty of fluids to rehydrate.

It’s important to note that these recommendations may vary depending on the individual athlete’s needs and the type of exercise they are performing. Consulting a qualified sports nutritionist or registered dietitian can help athletes tailor their fueling strategies to their unique needs.

Should triathletes do fasted or fed workouts?

Scientific literature defines fasted training as not eating within 10-14 hours before a workout.

For most athletes, this applies to their morning workout or to those who eat breakfast, then go all day without eating before an evening workout.

Some professionals say exercising on an empty stomach is the magic behind a leaner, meaner fat-burning machine, yet others warn against it. So, let’s sift through the chatter and find what works best for you.

RELATED: Is Time-Restricted Eating Safe for Athletes?

The benefits of fasted workouts

The allure of fasted workouts hinges on the promise of burning more fat as fuel, weight loss, a leaner physique, and enhanced performance. Sounds appealing, right?

Because glycogen stores are in limited supply, fasted training forces the body to utilize fat as fuel – which is the main objective. Over time with adaptation, the body becomes very good at burning fat for fuel as opposed to glycogen (stored carbs in the liver and muscles), providing sustainability during longer aerobic workouts. Reliance primarily on fat for fuel versus carbohydrates (carbs) delays the immediate risk of bonking and helps reduce dependence on supplemental fuel. All this to say, the theory of burning fat over carbs supports weight loss and a leaner physique – on paper anyway.

By and large, the research is clear; training in a fasted state improves the ability to tap into fat stores sooner and burn a higher percentage of fat during training sessions.

However, a caveat: the body is smart! In a fasted state, training the body to burn fat will also promote intramuscular fat storage, and over time, this plan will backfire.

Although fat is the primary fuel source in fasted, aerobic workouts (with glucose a close second), the body utilizes a blend of fuel sources (fat, carbs, and protein) for energy production, depending on the workout intensity and duration. In non-fasted endurance training, protein contributes approximately 5% of energy utilized. However, in fasted training, our muscle protein breakdown is double that in a non-fasting state. Repeatedly breaking down muscle tissue for energy leads to decreased resting metabolic rate, reduced strength, poor performance, and ultimately injury.

Training in a fasted state to delay or avoid bonking may sound like a good idea, but research warns it’s a major physiological stressor for the body. Athletes who train under-fueled experience elevated stress hormones such as cortisol. Elevated cortisol levels wreak havoc on the body, causing profound fatigue, poor recovery, abdominal fat storage, glucose intolerance, systemic inflammation, depressed thyroid function, and reducing your ability to relax or sleep. Break your fast by eating just enough to lower cortisol levels and top off blood glucose so the body doesn’t think it’s starving. Plus, having a small snack beforehand allows easy access to carbs and free fatty acids, so you can physically hit top-end efforts in training, enhancing fitness. Bottom line: If you don’t have carbs to pull from, the quality of your workouts will suffer by shortchanging your energy and ability to work hard.

As for the alleged endurance benefit that fasted training promises, research shows athletes who fueled before and during endurance sessions could perform aerobically for longer than in a fasted state.

Athletes tend to underestimate the body’s need for fuel and therefore sacrifice carbs in a carb-phobic world. Training under fueled can signal restricted eating and may lead to disordered eating or a full-blown eating disorder. Relative energy deficiency in sport (RED-S) or low energy availability is rampant among the athletic population from novice to pros. Any time an athlete restricts food to improve body composition or performance, it signals an alarm. Be mindful not to be led astray by concepts that involve withholding food/fuel from your body.

What female athletes need to know about fasted workouts

Research suggests the consequence of negative energy availability among female athletes comes at a higher price than their male counterparts. Not to suggest fasted training is appropriate for male athletes, but females have a different hormonal makeup that sets them apart. There is the follicular and luteal phase in the female monthly cycle, low and high hormones, respectively. In the luteal or high hormone phase (day 15-28), both estrogen (anabolic) and progesterone (catabolic) are elevated. Estrogen promotes fatty acid oxidation and spares glycogen. So, as you see, the female athlete is naturally an efficient fat burner since this occurs monthly for decades. In addition, progesterone dampens the body’s ability to store glycogen, so in the high hormone phase, when estrogen and progesterone are elevated, the body instinctively leans on fat over carbs for fuel. During the high hormone phase, fueling should be prioritized depending on the intention of the training session.

RELATED: Period Tracking for Female Athletes

When is it OK to train in a fasted state?

You are not alone if you can’t stomach eating before a run. So, it’s acceptable to go in a workout fasted – some of the time – as long as the effort is easy, 60 min or less in duration, the only workout of the day, and you are well hydrated.

On the other hand, topping off blood sugar after an all-night fast boosts blood glucose and energy, improves mental clarity and mood, allows the body to better access carbs and free fatty acids, and hinders muscle breakdown during the session. So, consider the intention of the workout before heading out the door without grabbing a quick bite.

RELATED: I’m Terrible About Eating Breakfast. How Can I Improve This Bad Habit?

Ideas for a quick snack – approximately 100 calories consisting of 20-25 grams easy to digest carbs, low fat, and fiber, with sodium and a small amount of protein. Examples include applesauce, white toast, banana, rice cake with jam and PB, one waffle, ½ sports bar, figs, dates, 2-3 sports chews, graham crackers, or vanilla wafers.

During high-intensity sessions and those lasting 75 min or more, it’s best to top off blood sugar before the workout. Fuel with a sports hydration beverage and possibly supplemental fuel during the session, depending on the duration and intensity. In addition, fueling provides an opportunity to test drive race day fueling/hydration and train the GI system to digest fuel at race-day efforts.

On long training sessions, it would be wise to simulate race day with a “pre-race” breakfast within a 1–3-hour window before you head out. Why wait until race day to test drive your pre-race meal when you have many opportunities in training?

Prioritize a post-workout snack within 45 minutes after high-intensity, long sessions, and strength-based workouts or if you cannot eat a meal after the workout. Aim for approximately 25-grams protein with simple carbs, low in fat and fiber.

The case against fasted workouts

Although fat is the primary fuel source in fasted, aerobic workouts (with glucose a close second), the body utilizes a blend of fuel sources (fat, carbs, and protein) for energy production, depending on the workout intensity and duration. In non-fasted endurance training, protein contributes approximately 5% of energy utilized. However, in fasted training, our muscle protein breakdown is double that in a non-fasting state. Repeatedly breaking down muscle tissue for energy leads to decreased resting metabolic rate, reduced strength, poor performance, and ultimately injury.

Training in a fasted state to delay or avoid bonking may sound like a good idea, but research warns it’s a major physiological stressor for the body. Athletes who train under-fueled experience elevated stress hormones such as cortisol. Elevated cortisol levels wreak havoc on the body, causing profound fatigue, poor recovery, abdominal fat storage, glucose intolerance, systemic inflammation, depressed thyroid function, and reducing your ability to relax or sleep. Break your fast by eating just enough to lower cortisol levels and top off blood glucose so the body doesn’t think it’s starving. Plus, having a small snack beforehand allows easy access to carbs and free fatty acids, so you can physically hit top-end efforts in training, enhancing fitness. Bottom line: If you don’t have carbs to pull from, the quality of your workouts will suffer by shortchanging your energy and ability to work hard.

As for the alleged endurance benefit that fasted training promises, research shows athletes who fueled before and during endurance sessions could perform aerobically for longer than in a fasted state.

Athletes tend to underestimate the body’s need for fuel and therefore sacrifice carbs in a carb-phobic world. Training under fueled can signal restricted eating and may lead to disordered eating or a full-blown eating disorder. Relative energy deficiency in sport (RED-S) or low energy availability is rampant among the athletic population from novice to pros. Any time an athlete restricts food to improve body composition or performance, it signals an alarm. Be mindful not to be led astray by concepts that involve withholding food/fuel from your body.

The Pros and Cons of Fasted Workouts

Invite Your Friends

You are on your way to feeling and becoming the best version of yourself! Invite your friends to join you in this journey. Share this useful guide with friends, and together, Improved Fat Loss, Performance, And Longevity Together!

Please fill out this form so we know where to send the FREE eBook

Privacy Policy: We hate spam and promise to keep your email address safe