What Does Your Body Burn First? The Truth Revealed!

A common misconception among many individuals is that the body burns fat first when attempting to shed some extra pounds. However, the process of burning fat is much more complex than that. The body has a priority list of fuel sources, which it burns for energy. It is crucial to understand which fuel sources the body targets first, as it can help you tailor your diet and exercise plan to maximize your efforts in your weight loss journey. In this article, we will dive into the question: What does your body burn first? The truth revealed!

The Order of Fuel Sources Burned by Your Body

When you eat food, your body undergoes a series of reactions to produce energy for daily activities. At rest, the body burns a combination of fat and carbohydrates for fuel. However, when you exercise, the body undergoes metabolic changes that increase the energy demand, and thus, the fuel source priority changes accordingly.

Glycogen Stored in Muscles and Liver

The first fuel source your body burns during exercise is glycogen. Glycogen is stored in both the liver and muscles and is a quick energy source for the body. The primary source of glycogen is carbohydrates that you consume through food. They are stored in the liver and muscles and are used when the energy demand is high during exercise.

  • Glycogen is the body’s primary source of energy for high-intensity activity that requires explosive movements, such as weightlifting or sprinting.
  • If you consume a high-carbohydrate meal, it will significantly increase your glycogen stores, which can enhance your performance during exercise.

Fat Stores in Adipose Tissue

After your body burns through the glycogen stores, it shifts its attention to the fat stores in your adipose tissue for energy. Fat is stored in adipose tissue all throughout your body and is the body’s largest source of energy reserves.

  • Contrary to popular belief, the body does not burn only stomach fat or love handles when losing weight. Fat is burned from all over the body.
  • The body prefers to burn fat during low-intensity exercises, such as jogging or walking, where the energy demand is low and prolonged.
  • The breakdown of triglycerides stored in the adipose tissue releases fatty acids and glycerol to be used as energy for the body.

Protein in Muscles

The body burns protein as a fuel source when both the glycogen stores and fat stores are depleted. Protein is crucial for building and repairing muscles, and the body only burns it as a fuel source when there are energy deficits in the body.

  • Burning protein for energy can lead to muscle loss, which is why it is crucial to avoid energy deficits when attempting to lose weight.
  • Low carbohydrate diets can cause increased protein oxidation, leading to muscle loss and a slowed metabolism.

Factors That Can Affect Your Body’s Fuel Source Priority

Exercise Intensity and Duration

The intensity and duration of exercise play a significant role in fuel source priority. When you perform high-intensity activities, such as weightlifting, your glycogen stores expend rapidly, and the body shifts to burn fat for energy.

  • The body burns approximately 70% of fat stores for energy during low-intensity exercise and 50% during moderate-intensity activities.
  • For longer exercise bouts such as marathon running or cycling, the body shifts to burn more fat for energy, conserving glycogen stores for later use.

Dietary Factors

The content and timing of meals also affect the body’s fuel source priority. Consuming a high-carbohydrate meal before exercise can enhance glycogen stores, leading to better performance and higher intensity workouts. However, a diet low in carbohydrates can lead to depletion of glycogen stores faster and shift the body’s attention to burn fat for energy.

  • Eating a diet rich in healthy fats can increase the body’s capability to burn fat stores for energy, leading to better weight loss results.
  • Consuming high amounts of protein can lead to increased oxidation of protein for energy, leading to a slowed metabolism and muscle loss.


It is crucial to understand the body’s fuel source priority and how it affects your weight loss goals. By understanding which fuel sources the body targets first, you can tailor your diet and exercise plan to maximize your efforts during weight loss. Remember, glycogen stores, fat stores, and protein all play a role in providing the body energy during exercise, and it’s essential to nourish your body with the right diet and adequate exercise.

Common Questions on What Does Your Body Burn First? The Truth Revealed!

  • What happens if you exercise on an empty stomach?
    If you exercise on an empty stomach, the body has to rely on the stores of glycogen and fat tissue to provide energy. However, it can lead to decreased energy levels and fatigue during exercise.
  • Does the body burn muscle before fat?
    No, the body burns fat before it burns muscle. However, if your calorie intake is dangerously low, the body can burn protein in the muscles for energy leading to muscle loss.
  • Can low carbohydrate diets lead to muscle loss?
    Yes, low carbohydrate diets can increase protein oxidation and lead to muscle loss. It’s crucial to maintain a healthy balance of macronutrients when losing weight for optimal results.
  • Is it possible to target specific areas of the body when burning fat?
    No, the body cannot target specific areas for fat burning. Fat stores are broken down throughout the body and used for energy.
  • Is breakfast the most important meal to fuel your body’s energy?
    No, each meal plays a crucial role in fueling the body. However, consuming a high carbohydrate meal before exercise can enhance glycogen stores and lead to better performance.


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