You can get away with not eating before an exercise session if it is low-intensity or less than an hour. If you haven't eaten for a few hours beforehand, it's important to have a balanced meal soon after (within an hour) to recover and refuel.
It is not recommended to workout if you don't have food in your system, as the body needs energy from food to sustain physical activity. Exercise can be taxing on the body and without proper fuel, you may experience weakness, fatigue, and decreased performance.
Exercising on an empty stomach or when hungry can lead to reduced performance and fatigue. Fueling your body with a balanced meal or snack containing carbohydrates and protein before exercise can provide energy and optimize performance.
Not eating after a workout can hinder recovery and muscle growth. It's essential to replenish your energy and provide your muscles with the nutrients they need. A light post-workout snack with protein and carbs will help you recover and support weight loss by boosting your metabolism.
But you can't treat a fast like it's any other day, especially when it comes to physical activity. “When you're physically active while fasting, you have a much higher risk of dehydration and heat illness,” she says. “It's something to be very cautious about.”
Yes, it is OK to work out while fasting because the key to weight loss and muscle gain is not just calories and exercise, but hormone optimization. Studies demonstrate amazing benefits to intermittent fasting alone, but combining fasting with sprint training takes the benefits of each to a whole new level.
So, running on an empty stomach helps our muscles use fat for fuel. This habit is great for burning more fat. By exercising without blood sugar, our body learns to use stored fat. This allows us to run longer and perform better, thanks to the energy from fat.
Overtraining and undereating can not only cause you to lose efficiency, but it can also cause you to lose muscle mass. If you have weight loss goals, eating less may sound like a good idea, but if it doesn't align with your fitness goals, you won't see the results you're hoping for.
Schlichter points to a review of 46 studies published in the Scandinavian Journal of Medicine & Science in Sports, which found that eating before exercise was beneficial for performance for aerobic workouts lasting more than an hour—though fasting before shorter workouts wasn't found to be detrimental.
Not eating after a workout at night can lead to low blood sugar, fatigue, and disorientation. Also, exercising subjects muscles to micro-tears which repair themselves to build strength. The body needs ample nutrition to repair itself via glycogen stores.
You eat 30 grams of protein within 30 minutes of waking up, followed by 30 minutes of “steady-state cardiovascular exercise.” Eating a protein-filled breakfast in the morning can stave off cravings later, and exercising first thing ensures you get some movement before your day gets going.
When you exercise in a fasted state — after a night's sleep and before you eat breakfast — then you do actually use more fat as a fuel source during exercise. But research from my team has shown that performing exercise in a fasted or fed state does not have any meaningful impact on body fat in the medium to long term.
Consider that food is fuel for your body. If you work out without fuel, you likely won't be able to train as intensely or for as long as you'd be able to with an adequate energy supply. Even if fasted cardio burns more fat, there's a chance that an overall decrease in performance would negate any potential benefit.
Your body uses stored fat and carbohydrates from food to fuel exercise. But when you haven't eaten for hours, there are fewer carbs available. So your body may rely on fat stores as a primary energy source, allowing you to burn more fat. The hormone cortisol stimulates fat metabolism.
However, exercising on an empty stomach will also cause you to lose lean muscle mass at the same time, which can hinder long-term weight loss. Exercising without eating first can cause dramatic shifts in your blood sugar, and when it drops quickly you can feel nauseous, light-headed or dizzy.
If you are training for muscle strength, and trying to lift as much as possible, you probably do not want to run out of glycogen. There is little endurance required for this activity and explosive quick energy is needed so feeding beforehand is ideal.
Fasting combined with physical activity did not affect the effects of training on muscle performance.
You're depriving your muscles of the amino acids they need to rebuild and recover. You're not replenishing the stored glucose (glycogen) in your muscles which can lead to further muscle breakdown. You'll get hungry a few hours later and likely overeat at that later meal.
You can get away with not eating before an exercise session if it is low-intensity or less than an hour. If you haven't eaten for a few hours beforehand, it's important to have a balanced meal soon after (within an hour) to recover and refuel.
There are other terms for this, such as build mode, but bulking is a common term for this caloric surplus. Dirty bulking is when an individual is in a caloric surplus to build muscle (build mode). However, the individual is eating foods that are carb dense, unhealthy, and ultra-processed out of convenience.
Symptoms and warning signs of overtraining
“It's natural and expected to feel fatigued after challenging training sessions,” Dr. Goolsby says. “But feeling like you aren't recovering between sessions or experiencing overall fatigue and difficulty pushing yourself during workouts can be indicators of overtraining.”
I have heard that exercising on an empty stomach burns more fat and at a faster rate. Is this true? Research using healthy young men has shown that doing aerobic exercise when fasting increases the use of stored fat as an energy supply. The reaction may be related to the low insulin levels that occur during fasting.
You might be wondering, how long does it take for your stomach to empty? After a meal, it normally takes around 1 hour and 30 minutes to 2 hours for your stomach to empty. But, the type of meal you eat plays a role in how fast it moves through your stomach.
Ideally, fuel up two hours before you exercise by:
Eating healthy carbohydrates, such as whole-grain cereals (with low-fat or fat-free milk), whole-wheat toast, low-fat or fat-free yogurt, whole-grain pasta, brown rice and fruits and vegetables. Avoiding saturated fats and proteins, even healthy ones.