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Is It Bad to Work Out on an Empty Stomach?

    One ever-growing belief among exercisers is that working out on an empty stomach can electrify their metabolism and accelerate their weight loss process. However, you can’t solely rely on the rumors and need a more scientific answer. So is a fasted workout beneficial or bad for your health and overall performance?

    It’s bad to work out on an empty stomach as it can lead to bonking, low insulin, muscle loss, and other side effects. However, if you keep the workout short, moderate, and irregular, some fat loss benefits would take effect. You must also eat carbs and protein after and a few hours before the session.

    Read on to see how a fasted training method can affect your weight loss program. You’ll also learn about its adverse effects on the body and when you’re free to do it.

    Exercising in a Fasting State: The Evidence

    A handful of studies support this theory that exercising in a fasted state leads to greater fat loss than in a fed state.

    The British Journal of Nutrition, for example, has an intervention study that proves it can make a 20 percent improvement in the fat loss process. Another 2016 study also indicates empty stomach in aerobic workouts can heighten your fat oxidation and weight loss effects.

    The experimental research by the Ministry of Education and the University of Bath also tested the theory on obese men, concluding that fast training can help weight loss by activating specific genes and burning more stored fat.

    Yet, contradictory papers nullify all these findings or suggest further research is needed before we adopt this fasting approach.

    The International Journal of Sport Nutrition and Exercise Metab showed those skipping breakfast or meals before training sessions would face a huge performance drop. This is while trainers with low fat and low carb meal before exercise are proven to do better, faster, and longer.

    Some papers proclaim training while fasting is not only ineffective but also dangerous or counterproductive. 

    Here’s why you shouldn’t workout on an empty stomach, even if it proves beneficial for weight loss:

    Disadvantages of Working Out While Fasting

    Even if a fasted workout can boost your fat-burning process, it’s not ideal because the downsides exceed its benefits. Also, the pro articles have only proved its effectiveness in the short term. But in the long term, it can dispel whatever you’ve gained, affecting both your weight and overall health.

    Some of the most seen pitfalls of working out on an empty stomach include:

    Blood Sugar Reduction

    Blood sugar or insulin is a hormone produced as a result of food consumption. When you haven’t eaten for a while, your baseline insulin level is already low and can drop to dangerous levels as soon as you start training.

    At this point, you may feel exhausted, shaky, dizzy, and nauseous. And in the worst-case scenario, it can lead to a hypoglycemic condition where you faint and lose consciousness. This is especially threatening when training outdoors or via equipment.

    This can even cause vitamin deficiencies, heightened stress levels, and a weak immune system when done regularly.

    Not only that, training with an empty stomach can overtax your body, tire out the muscles, and as a result, make you more hungry than usual. So, you’ll eat more, and all your efforts will go down the drain.

    Muscle Scarification

    The assumption of more fat loss in fasted training comes from this procedure: Our body supplies its required energy during a workout from the stored glycogen in our muscles and liver. And this glycogen is produced from the glucose (carbs) you consume.

    When you’ve not eaten for some hours, your body depletes this fuel, and as a result, it reaches out to other valuable energy sources.

    In an ideal world, this alternative source would be visceral fat around your belly. But That’s not always the case. Sometimes, your body starts breaking down your muscle fibers to take its protein. And you’ll end up losing muscle mass rather than gaining it, due to medical articles.

    What makes it even worse is that you’ll lack enough protein to repair the torn muscles afterward—something necessary for building muscles.

    This risk can manifest itself, especially in weightlifting or any kind of intensive cardio.

    Dehydration and lightheadedness are other symptoms of this muscle loss.

    Not Suitable for HIIT

    Even if your body sticks out to your fat reserves (instead of protein) to recuperate its energy deficiency, this procedure may take so long that it won’t succeed.

    That’s because mobilizing fat is more challenging than activating glycogen. So, it demands more oxygen, and consequently, more time to break down fat.

    This slowed rate of burning means you won’t immediately access enough fuel in the lack of carbohydrates. So, you may hit the wall in the middle of the exercise and become unable to finish the sets—according to Katie Kissane, a registered sports dietitian, and endurance specialist.

    When It’s Safe to Work Out on an Empty Stomach

    So far, we’ve talked about why and how fasted training can harm your body and workout performance. However, there might be a time where you don’t have enough time to eat before training. This mostly happens to busy bees who want to squeeze a quick workout into their morning before going to work.

    In that case, there are a few ways that you can repeal those risks and work out safely with an empty stomach.

    Do It only for Steady-State

    Alexandra Cook, a sports dietitian with 13 years of experience, says you cannot hit the intense training zone without a carb-based pre-workout intake. 

    That’s because, in the absence of glucose, your body requires more energy to tap into alternative fuel. But since you’re working hard, your HR is already at the highest, and it may not be able to pump faster to supply that much oxygen.

    Therefore, it’s more likely to exploit your muscles rather than stored fat.

    But if you switch to a steady-state aerobic exercise, your body has enough time to transmit the needed oxygen and gradually exploit your stored fat.

    Besides, even if it doesn’t reach the stored fat, your body has enough stored glucose for a one-hour steady-state. So you’ll be fine.

    Here’s a sample steady-state cardio to follow:

    Keep It Short

    The International Journal of Sports Medicine believes you won’t bear the risks of fasted training as long as you keep it moderate and less than half an hour. Besides that, you’re not allowed to do it over twice a week.

    Focus on Your Last-Night Meal

    It’s fine to work out the first thing in the morning, but only provided that you ate a proportionate meal the night before. This way, your glycogen depositions don’t completely drain during the sleeping phase, and you’ll have a fair amount of it for at least the first few minutes of training—before your body searches for its alternatives.

    But remember to include an adequate amount of carb, fat, and protein in your last-night dinner. 

    Include a Post-workout Meal

    Post-workout dietary habits matter a lot when it comes to the effectiveness of a certain exercise. But they gain even more meaning when you skip the pre-workout meal. That’s because your body remains in dire need of nutrients to replenish the depleted glucose stores and to recuperate the potentially lost muscles.

    Protein is the most important nutrient to eat in this phase. But you would also want to contain a quick source of carbs in it.

    Drink Water

    Working out on an empty stomach can remain harmless if you meet a few requirements, but working out with a dehydrated body is by no means reasonable or safe. It weakens and fatigues your muscles and can lead to more severe cases such as unregulated body temperature, heat stroke, kidney failure, or seizure.

    Make sure you always have a water bottle with you when working out. I recommend the 40-ounce Iron Flask available on Amazon. It comes with three different lids, and the double insulation keeps your drinks both cold and sweat-free. 

    Iron Flask Sports Water Bottle - 40 Oz, 3 Lids (Straw Lid),Vacuum Insulated Stainless Steel, Double Walled, Thermo Mug, Metal Canteen
    • INSULATED SPORTS WATER BOTTLE: Goodbye sweat! The double wall insulation makes the Iron Flask sweat-free! It keeps your drink COLD for up to 24 hours, and HOT for up to 12 hours. *NOTE: ONLY the 14 Oz, 18 Oz, & 22 Oz fit in cupholders*
    • 3 LIDS: YES, Iron Flask comes with THREE different lids. Carabiner Straw Lid with 2 Straws, Flip Lid, and a Stainless Steel Lid! *NOTE: The stainless steel lid is plastic from inside and stainless steel from outside*

    Alternatively, you can go for the Pogo BPA-Free Plastic bottle, which comes in a variety of colors and features a leak-proof chug lid. The material contains no BPA, phthalates, PVC, lead or cadmium. So, you don’t have to worry about digesting dangerous materials. 

    So, drink plenty of fluids before, during, and after your training session. And ideally, try to add some electrolytes into your water—making detox water with strawberries, oranges, grapefruit, mint, and ginger is a practical way.

    Listen to Your Body

    That said, the above rules may not apply to everyone alone. Depending on your living habits and physique, some people may run out of glycogen sooner than others. So, they may not be ideal for a fasted workout style.

    For example, you may sleep more than the standard eight hours. Or, you may eat dinner so early that nothing remains as energy in the morning after.

    So, the best rule is to listen to your body and stop training if you feel light-headed or sick in any form.

    So What Is the Best Diet When Exercising

    Just the way training with an empty stomach is harmful, doing so with a full stomach can take its toll on your performance, and you should avoid it as much as possible.

    This way, your body gets enough fuel to recruit your muscles, and simultaneously, it doesn’t have to spend it on digesting the extra food. So, all its attention shifts to the fat-burning or muscle-building process.

    In an ideal world, you have to eat about an hour ahead of starting your session. Also, limit the pre-workout meal to a few slices of fruits (bananas, berries, apples, or avocados), nuts (almond or peanut), smoothies, or protein shakes. Then postpone the larger meals (chicken, rice, and steamed greens) to the post-workout phase.

    Here’s a list of what to eat for endurance, strength, and weight loss workouts specifically:

    What to eat

    Here’s what to generally eat before and after each session:

    Workout Diet

    Final Thoughts

    Although some studies remain in favor of fasted exercise, it doesn’t mean it’s the best you can do.

    Firstly, these studies are done in a limited scope—for obese, highly activated, or ill people—and need further support. Besides, even if they do encourage fat loss, there’ll be some functional or physical tradeoffs.

    Make sure you eat a light snack before your workouts. If not possible, at least eat a large portion of protein and carbs after the workout and the night before the exercise. Don’t work out on an empty stomach more than a few times a month, and only adopt short steady-state sessions when you do.

    Last update on 2022-10-13 / Affiliate links / Images from Amazon Product Advertising API


    James Wright

    James (36) has been working out since he was 15 years old. He has a home gym where he pumps iron, does bodyweight workouts and boxing. He likes sharing his experiences with others who want to build a better physique.

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