HIIT on an Empty Stomach – Good or Bad Idea?

Last updated on June 18th, 2020

Time to Read: 7 minutes

High-intensity interval training (HIIT) triggers rapid adaptation of the body by combining short bursts of intense workouts. Forced adaptation improves muscle tone, cardiovascular function, weight loss, and bone mineral density. HIIT exercises can incorporate aerobic and resistance training. The high levels of intensity are coupled with minimal downtime, requiring a significant amount of energy to perform. This begs the question, is HIIT on an empty stomach a bad idea?

High-intensity exercise yields quality workouts in the least amount of time. Short and long-distance runners prepare for races by engaging in interval training to boost endurance. HIIT enables them to alternate between jogging and sprints. It comes as no surprise that high-intensity interval training has become part of the mainstream. Many research studies confirmed the wide-ranging benefits of HIIT

HIIT on an Empty Stomach – Bad Idea?

The ability to work out on an empty stomach depends on two factors: type of exercise and the duration of the workout. Many people have little time to eat before an early morning HIIT, while others avoid breakfast before a workout because it makes them feel sick.

Performing HIIT exercises in a fasted state may make your body more efficient at burning fat. However, there are conflicting claims about the fat-burning benefits of working out on an empty stomach. Some reports show that the body burns fat efficiently in a fasted state since it relies on fat as a source of fuel.

Overall, working out on an empty stomach during shorter HIIT workouts is feasible. Your body takes advantage of your fat stores for energy. This approach may be unsuitable for lower intensity exercises that last more than one hour.

Shorter HIIT workouts can boost growth hormone (GH) production, which contributes to an increase in muscle mass, bone density, and weight loss. Some reports also show that fasted training has an indirect impact on testosterone levels. Increased testosterone levels help reduce body fat, boost energy, and enhance lean muscle gains.

Pros and Cons of Performing HIIT on an Empty Stomach

hiit on an empty stomach

Doing HIIT exercises on an empty stomach has its fair share of advantages and disadvantages. This approach is not a one-size-fits-all option; hence, the need to take into account your training requirements and objectives.

Pros of HIIT on an Empty Stomach

Although opinion is divided on the pros and cons of fasted training, you can derive some benefits from exercising before breakfast.

Some of the key benefits of training on an empty stomach include improved hormonal output, fat loss, and nutrient absorption (post-workout meals). Fasted training requires careful consideration when looking to enhance athletic performance, muscle gain, fat loss, and body composition.

Boost Hormonal Output

Hormones play a crucial role in the functioning of various parts of the body. They enhance physical performance, help burn fat, and build lean muscle mass. Training in a fasted state for short periods does not impede hormonal activity, which may help you achieve specific fitness or weight loss goals.

When you perform HIIT workouts in a fasted state, the intensity triggers an array of hormonal activity, including improved insulin sensitivity, testosterone, and growth hormone levels. Reduced food consumption prompts the body to limit the release of insulin. This reduction enhances sensitivity to the limited insulin released during fasting, which makes it easier to burn fat.

Post-exercise Benefits of HIIT on an Empty Stomach

During the post-workout phase, the body works overtime to replenish the depleted glycogen and oxygen reserves. The replenishment process lasts for several hours, and it helps burn a significant amount of fat in your body than during training. The process can continue even throughout the night and the following morning.

Improved Performance During HIIT workouts

A combination of HIIT workouts and short periods of fasting leads to an anabolic hormonal state. As a result, your body releases increased fat reserves as a fuel source during the high-intensity exercises. The anabolic hormonal state also helps build lean muscle.

Training on an empty stomach is a practical option for exercises, such as powerwalking and resistance training. It is also ideal for endurance athletes because it allows the body to change the way muscles store glycogen (fuel). The adaptation makes it easier to cope with the rigors of long-distance races.

Improved Nutrient Absorption

Doing fasted HIIT workouts has a positive effect on the absorption of nutrients when consuming meals after exercise. Fasted training enhances the body’s ability to digest, partition, and use nutrients. Your body maximizes the absorption of essential macronutrients, such as fats, carbs, and proteins. In turn, you will find it easier to build lean muscle and burn fat.

Cons of HIIT on an Empty Stomach

While fasted training can yield some significant benefits, it comes with several downsides that you need to consider carefully. For this reason, exercising on an empty stomach may be a bad idea for some scenarios.

Rapid Depletion of Glycogen Reserves

During HIIT exercises, your heart rate skyrockets, and the body consumes fuel rapidly, which undermines its ability to breakdown carbohydrates from scratch. In such cases, your muscles rely on glycogen reserves as a readily available fuel source. The rapid depletion of these reserves leads to a drop in glucose levels.

To maintain balance, the body resorts to pumping glucose back into the bloodstream. However, the rate at which the body re-supplies glucose into the bloodstream is slower than the rate of consumption. This deficit can lead to fatigue.

Fat Burning Complexities

On the other hand, your body may struggle to burn fat on an empty stomach because it metabolizes carbs easier than fat. Exercises like walking are more efficient at utilizing carbohydrates for producing energy.

Breaking down fat is a metabolically complex process, which may not happen as quickly as you want during exercises. While it is possible to burn fat when doing HIIT workouts in a fasted state, you cannot rely on the fat reserves to provide energy for your muscles, given the high-intensity training. The fat may trace back to the fat cells.

HIIT routines lasting 20 minutes or less have been shown to provide an efficient way to burn calories. On the downside, the ability to burn calories does not automatically translate to weight loss. Researchers discovered that higher intensity exercises trigger increased disturbance of the body’s homeostasis. In the end, athletes require high levels of energy and oxygen to restore the body’s normal state.


Performing intensive exercise on an empty stomach can have negative effects on your ability to maintain composure. Your stomach may cramp easily, and you could feel light-headed or dizzy during training. In the end, it becomes easier to fall or suffer serious injuries.

Another possibility is that your body may drift into a hypoglycemic state, and you may lose consciousness due to low blood sugar levels. Your performance suffers when you are hungry and feeling lethargic due to low blood sugar. In many cases, fasted workouts can trigger increased stress on the body. You are more likely to find it difficult to stay motivated.

Catabolic State

Without the boost from a pre-workout meal, your body may convert muscles to energy. Although the intensive exercise will help burn fat, you may enter the catabolic state, which is the opposite result of your training regime. During fasted training, the body does not tap into fat reserves alone. It’ll break down both muscle and fat.

Overnight, the body enters the catabolic state as it relies on the muscle to obtain essential nutrients. By doing intensive exercises in the morning before consuming any food, you accelerate muscle loss.

You can reduce the effects of catabolism by eating before your workout and increasing your protein intake, especially for adults over the age of 55. Older adults face an uphill battle when it comes to building and retaining lean muscle mass. As such, it is vital to avoid muscle loss during intensive exercises.

Top Tips for Fasted HIIT Workouts


Training on an empty stomach is a practical option if you exercise in the morning rather than in the afternoon or evening. To maximize performance, consume a large amount of micro- and macronutrients the previous night. The meal should also incorporate calories. However, avoid takeout or junk food.

Drinking plenty of water before exercising on an empty stomach keeps you hydrated during the intensive workout. Opt for water with branched-chain amino acids (BCAAs) or electrolytes to boost the intake of essential nutrients.

The ideal fasted training strategy involves drinking at least 16 ounces (500 milliliters) of water early in the morning. Also, consider drinking a cup of espresso or coffee before training. Prepare your post-workout meal, including a snack or shake. Check out our guide on what to eat before a workout for more information on maximizing your workout effectiveness through nutrition.

During HIIT exercises, consume water, preferably with BCAAs or electrolytes.

Your post-exercise meal should include proteins and carbohydrates. Consume the food less than one hour after training and continue drinking plenty of water. As you rest and recuperate, pay attention to your sleep patterns and your body’s response to the workouts. Any drastic changes to your sleep patterns may be a sign of adverse reaction. 

During the post-workout recovery phase, your body should feel sore rather than excessive pain. The intensity of your HIIT exercises determines the amount of water you should drink after training. The general rule is to drink at least 16 ounces (500 milliliters) for every pound you shed during exercise.