Does exercising on an empty stomach boost fat loss? Here's what you need to know

You roll out of bed, lace up your sneakers, and hit the gym.

There’s no breakfast in sight.

That’s a tad intense, but working out on an empty stomach, also known as ‘fasted cardio,’ could be the secret weapon for burning fat, boosting endurance, and feeling great. While some people can’t imagine breaking a sweat without a pre-workout snack, others swear by the magic of training in a fasted state.

And science backs these claims.  A study from Nottingham Trent University found that participants who exercised on an empty stomach burned nearly 70 per cent fat than those who worked out two hours after eating.

So, should you skip breakfast before a workout? Let’s break it down.

The science behind fasted workouts

The benefits of exercising on an empty stomach are undeniable. Mathilde Valade, Osteopath, Wellth, explains: “When you exercise in a fasting state, your body is encouraged to use fat stores for energy as glycogen levels are lower. Your body uses stored fat as its main energy source when you exercise without eating. This could potentially boost fat burning and aid in weight loss. Moreover, it may enhance insulin sensitivity, which can be beneficial for metabolic health and reduce the risk of insulin resistance.”

Another key benefit? Fasted workouts can increase the secretion of growth hormone, which plays a major role in fat metabolism, tissue repair, and muscle recovery.

Does it really lead to more fat loss?

While fasted exercise may boost fat oxidation, does it lead to greater weight loss? Cynthia Bou Khalil, Dietitian at Medcare Dr. Saeed Al Shaikh Gastro and Obesity Centre, weighs in. “While fat oxidation may increase during fasted exercise, this does not necessarily translate to greater long-term weight loss. Weight loss depends on overall calorie balance and lifestyle factors. Some individuals may compensate by eating more later in the day.”

However, she also clarifies that fasted cardio doesn’t necessarily mean you’re following an intermittent fasting routine. It could simply be going for a morning run before breakfast. Exercising after an overnight fast of 8 to 12 hours can help burn up to 20 per cent more fat. This happens because fasting lowers blood sugar, insulin, and glycogen storage. Normally, our bodies rely on glycogen. derived from dietary carbohydrates, for energy. But in a fasted state, with depleted glycogen levels, your body is more likely to tap into stored fat for fuel.

Potential drawbacks and considerations

Khalil explains that while working out on an empty stomach has benefits, it can also be harmful, especially if done inappropriately or by individuals with certain medical conditions. "Hypoglycemia, or low blood sugar levels, can cause dizziness, weakness, and even fainting during exercise, increasing the risk of accidents or injuries. Prolonged fasting exercise without proper nourishment can also lead to muscle breakdown, particularly if done regularly. This is especially problematic for those looking to build muscle, as they may not have enough fuel to support muscle growth and recovery."

She further emphasises that excessive fasted exercise can be counterproductive:

 "If your glucose levels are too low, you may not have enough energy to perform at your best. And if you don’t eat a proper meal after your workout, you might end up losing muscle instead of gaining strength."

Valade outlines some potential drawbacks of working out in a fasted state:

Reduced performance and energy levels: Low glycogen stores can impair performance, especially in high-intensity or endurance exercises, leading to quicker fatigue.

Increased cortisol levels: Fasted exercise can elevate cortisol, the body's stress hormone, which may negatively impact recovery and muscle preservation.

The role of insulin and glycogen levels in workouts

Insulin plays a crucial role in nutrient storage and utilisation. In a fasted state, insulin levels are lower, which may encourage fat oxidation. However, glycogen stores are also depleted, potentially limiting performance in high-intensity workouts.

For endurance athletes and those engaging in resistance training, low glycogen levels can lead to reduced strength, power, and recovery. While fasted workouts may work for some, they may not be ideal for individuals who require sustained energy for prolonged or intense exercise.

Does it lead to more muscle loss?

Exercising on an empty stomach can lead to lean muscle loss, which isn’t ideal for long-term weight loss, toning, or overall body composition. However, as Khalil explains, it’s not just about skipping food before a workout, it’s about what you eat afterward.

Properly refueling with enough protein throughout the day helps muscles recover and prevents muscle loss. As she explains, research on intermittent fasting support this, showing that as long as you consume adequate protein post-workout, fasted exercise won’t necessarily break down muscle.

Valade adds that while short, moderate-intensity workouts are generally safe in a fasted state, prolonged or high-intensity sessions without proper nutrition can increase protein breakdown, potentially leading to muscle loss.

Should you try fasted workouts? It depends

As both the experts say: Fasted exercise may provide metabolic benefits, but is not necessary for everyone. People with specific health concerns, those engaging in high-intensity training, or those prone to fatigue should approach fasted workouts cautiously. Hydration, proper post-exercise nutrition, and listening to the body's signals are essential to maintaining optimal performance and overall well-being.

Ultimately, whether fasted workouts are right for you depends on your goals and health needs. If you’re curious, it’s worth experimenting, but always prioritise hydration, nutrition, and listening to your body.