Exercising in a fasted state may help burn more fat, but it can also cause the body to burn muscle for fuel in addition to fat. Even if the percentage of muscle burnt is comparatively small, it can be detrimental to the long-term success of any weight- or fat-loss program.
When you exercise on an empty stomach, your body is forced to break down muscle for energy. This can lead to muscle loss and decreased metabolism. Additionally, you may experience fatigue and low blood sugar, which can make it difficult to complete your workout.
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.
You don't need to burn muscle instead of fat, nor will your body automatically burn muscle while fasting. It's possible to lose a bit of muscle mass when you fast, as you also lose water weight and visceral fat. However, it's more likely you'll maintain muscle mass rather than lose or gain it.
Furthermore, there is nothing wrong with weight training on an empty stomach. Your workouts are fuelled through your glycogen stores, which will typically provide enough energy for a good 30-40 minutes (glycogen is produced by the liver from excess ATP and excess glucose).
You May Lose Muscle
And these stores aren't restored until you eat a meal with carbohydrates. When you don't have enough glycogen stored in your muscles, your body needs to rely on other sources of energy, including your own fat and muscle tissue.
The degree of this overload ultimately determines the degree of muscle growth. Muscle "burn" does not stimulate growth, overload stimulates growth. The burning sensation that training brings on is believed by most to be a sign of a successful growth promoting workout.
Many studies have shown that during fasting, muscle loss doesn't occur, whereas others have. To be safe, ensure a protein-rich meal before bed with carbohydrates, fat and fibre to slow digestion, if you're looking to fast the next day for 24 hours and you're not training. This will ensure no muscle loss occurs.
The Potential Drawbacks of Fasted Weight Lifting
One 2016 study found that men who followed an eight-week weight training plan while fasting for 16 hours a day lost some body fat, but didn't gain any strength. Their testosterone levels lowered, and their cortisol levels rose, too.
This burning sensation is associated with a buildup of acid in the muscles during intense exercise, and lactic acid has long been thought to be the culprit in that acid buildup, known as acidosis. Lactic acid is a byproduct of anaerobic metabolism, in which the body produces energy without using oxygen.
Weight Management or Weight Loss - Whilst fasted training may enhance fat oxidation, it does not result in greater overall weight loss, decreased fat mass or changes in lean muscle, when compared to fed training of equal calorie intake. Nor does it 'Boost metabolism'.
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.
"A person who is attempting to lose weight by not eating may lose weight in muscle first before fat," he says. How does that happen? Well, the body likes to go for carbs (glucose) for energy first.
To make gains you have to have the right nutrients in your body to construct muscle. This means that what you eat, and how much, is essential in making muscle gains. Lifting and doing strength training without adequate nutrition, especially without enough protein, can actually lead to loss of muscle tissue.
Potential side effects could also include dizziness or nausea. Exercising in a fasted state may help burn more fat, but it can also cause the body to burn muscle for fuel in addition to fat.
Exercising in the morning can lead to increased alertness and mental clarity, which may enhance productivity throughout your day. However, it's important to warm up properly, as the body's muscles are typically colder and tighter in the morning.
Limited research into intermittent fasting paired with regular resistance training suggests that while someone who is intermittent fasting may lose more weight than someone on a regular diet, their muscle gains and maintenance will be largely identical.
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.
Lifting weights, sprinting, doing CrossFit WODS, and other high-intensity activities all depend on carbohydrates for fuel, explains Poli. If you perform any of these activities during (or worse, at the end of) your fast, your performance will suffer.
Gaining muscle and not losing fat often comes down to diet. It's possible that you're eating too much and may need to decrease your calories slightly. You'll also need to analyze your workouts and overall daily activity levels and consider adding in more calorie-burning activities to boost your fat loss efforts.
If you're not training hard enough, progressing, or you're overtraining, you can see muscle mass go down, even if you're in the gym everyday. If your calories or protein are too low, you will see a decrease in muscle mass, even if you are getting stronger.
That said, the one true way to identify whether or not you're losing muscle is to measure your body composition. The most accurate ways to measure your muscle versus fat involve some pretty fancy techniques (like x-ray scans called DEXAs or underwater weighing), says Oldham Carnes.
This usually involves doing exercises such as squats, lunges, and leg presses to strengthen and shape the muscles. Being strong is good. Tone can also be improved by reducing weight, as muscle tone is more defined with less adipose or fatty tissue around it. Excess fat will accumulate around the muscles.
So if you regularly exercise and find you aren't feeling as sore later in the day or even in the days after your workout, rest assured that your workout is still working – your muscles have just gotten better at dealing with the damage and recovering from it.